diff --git a/.vscode/launch.json b/.vscode/launch.json
new file mode 100644
index 0000000..7c60ee4
--- /dev/null
+++ b/.vscode/launch.json
@@ -0,0 +1,14 @@
+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "bitcoin_flutter",
+            "request": "launch",
+            "type": "dart",
+            "program": "example/bitcoin_flutter_example.dart",
+        }
+    ]
+}
\ No newline at end of file
diff --git a/lib/bitcoin_flutter.dart b/lib/bitcoin_flutter.dart
index a77de46..005543c 100644
--- a/lib/bitcoin_flutter.dart
+++ b/lib/bitcoin_flutter.dart
@@ -1,13 +1,12 @@
 /// Support for doing something awesome.
 ///
 /// More dartdocs go here.
+// @dart=2.12
 library bitcoin_flutter;
 
 export 'src/bitcoin_flutter_base.dart';
 export 'src/models/networks.dart';
-export 'src/transaction.dart';
 export 'src/address.dart';
-export 'src/transaction_builder.dart';
 export 'src/ecpair.dart';
 export 'src/payments/p2pkh.dart';
 export 'src/payments/p2wpkh.dart';
diff --git a/lib/src/address.dart b/lib/src/address.dart
index c310f12..2736d88 100644
--- a/lib/src/address.dart
+++ b/lib/src/address.dart
@@ -7,7 +7,7 @@ import 'payments/p2pkh.dart';
 import 'payments/p2wpkh.dart';
 
 class Address {
-  static bool validateAddress(String address, [NetworkType nw]) {
+  static bool validateAddress(String address, [NetworkType? nw]) {
     try {
       addressToOutputScript(address, nw);
       return true;
@@ -16,7 +16,7 @@ class Address {
     }
   }
 
-  static Uint8List addressToOutputScript(String address, [NetworkType nw]) {
+  static Uint8List addressToOutputScript(String address, [NetworkType? nw]) {
     NetworkType network = nw ?? bitcoin;
     var decodeBase58;
     var decodeBech32;
@@ -24,25 +24,21 @@ class Address {
       decodeBase58 = bs58check.decode(address);
     } catch (err) {}
     if (decodeBase58 != null) {
-      if (decodeBase58[0] != network.pubKeyHash)
-        throw new ArgumentError('Invalid version or Network mismatch');
-      P2PKH p2pkh =
-          new P2PKH(data: new PaymentData(address: address), network: network);
-      return p2pkh.data.output;
+      if (decodeBase58[0] != network.pubKeyHash) throw ArgumentError('Invalid version or Network mismatch');
+      P2PKH p2pkh = P2PKH(data: PaymentData(address: address), network: network);
+      return p2pkh.data.output!;
     } else {
       try {
         decodeBech32 = segwit.decode(address);
       } catch (err) {}
       if (decodeBech32 != null) {
-        if (network.bech32 != decodeBech32.hrp)
-          throw new ArgumentError('Invalid prefix or Network mismatch');
-        if (decodeBech32.version != 0)
-          throw new ArgumentError('Invalid address version');
-        P2WPKH p2wpkh = new P2WPKH(
-            data: new PaymentData(address: address), network: network);
-        return p2wpkh.data.output;
+        if (network.bech32 != decodeBech32.hrp) throw ArgumentError('Invalid prefix or Network mismatch');
+        if (decodeBech32.version != 0) throw ArgumentError('Invalid address version');
+        P2WPKH p2wpkh = P2WPKH(data: PaymentData(address: address), network: network);
+        if (p2wpkh.data.output == null) throw ArgumentError('p2wpkh.data.output is null');
+        return p2wpkh.data.output!;
       }
     }
-    throw new ArgumentError(address + ' has no matching Script');
+    throw ArgumentError(address + ' has no matching Script');
   }
 }
diff --git a/lib/src/bitcoin_flutter_base.dart b/lib/src/bitcoin_flutter_base.dart
index 6de8167..8d9cca4 100644
--- a/lib/src/bitcoin_flutter_base.dart
+++ b/lib/src/bitcoin_flutter_base.dart
@@ -1,143 +1,127 @@
 // TODO: Put public facing types in this file.
 import 'dart:typed_data';
+
+import 'package:bip32/bip32.dart' as bip32;
 import 'package:bitcoin_flutter/src/utils/magic_hash.dart';
 import 'package:hex/hex.dart';
-import 'package:bip32/bip32.dart' as bip32;
+
+import 'ecpair.dart';
 import 'models/networks.dart';
 import 'payments/index.dart' show PaymentData;
 import 'payments/p2pkh.dart';
-import 'ecpair.dart';
-import 'package:meta/meta.dart';
-import 'dart:convert';
 
 /// Checks if you are awesome. Spoiler: you are.
 class HDWallet {
-  bip32.BIP32 _bip32;
-  P2PKH _p2pkh;
-  String seed;
+  bip32.BIP32? _bip32;
+  P2PKH? _p2pkh;
+  String? seed;
   NetworkType network;
 
-  String get privKey {
-    if (_bip32 == null) return null;
+  String? get privKey {
+    if (_bip32?.privateKey == null) return null;
     try {
-      return HEX.encode(_bip32.privateKey);
+      return HEX.encode(_bip32!.privateKey!);
     } catch (_) {
       return null;
     }
   }
 
-  String get pubKey => _bip32 != null ? HEX.encode(_bip32.publicKey) : null;
+  String? get pubKey => _bip32?.publicKey != null ? HEX.encode(_bip32!.publicKey) : null;
 
-  String get base58Priv {
+  String? get base58Priv {
     if (_bip32 == null) return null;
     try {
-      return _bip32.toBase58();
+      return _bip32!.toBase58();
     } catch (_) {
       return null;
     }
   }
 
-  String get base58 => _bip32 != null ? _bip32.neutered().toBase58() : null;
+  String? get base58 => _bip32 != null ? _bip32!.neutered().toBase58() : null;
 
-  String get wif {
+  String? get wif {
     if (_bip32 == null) return null;
     try {
-      return _bip32.toWIF();
+      return _bip32!.toWIF();
     } catch (_) {
       return null;
     }
   }
 
-  String get address => _p2pkh != null ? _p2pkh.data.address : null;
+  String? get address => _p2pkh != null ? _p2pkh!.data.address : null;
 
-  HDWallet(
-      {@required bip32, @required p2pkh, @required this.network, this.seed}) {
+  HDWallet({required bip32, required p2pkh, required this.network, this.seed}) {
     this._bip32 = bip32;
     this._p2pkh = p2pkh;
   }
 
   HDWallet derivePath(String path) {
-    final bip32 = _bip32.derivePath(path);
-    final p2pkh = new P2PKH(
-        data: new PaymentData(pubkey: bip32.publicKey), network: network);
+    final bip32 = _bip32!.derivePath(path);
+    final p2pkh = P2PKH(data: PaymentData(pubkey: bip32.publicKey), network: network);
     return HDWallet(bip32: bip32, p2pkh: p2pkh, network: network);
   }
 
-  HDWallet derive(int index) {
-    final bip32 = _bip32.derive(index);
-    final p2pkh = new P2PKH(
-        data: new PaymentData(pubkey: bip32.publicKey), network: network);
+  HDWallet? derive(int index) {
+    if (_bip32 == null) return null;
+    final bip32 = _bip32!.derive(index);
+    final p2pkh = P2PKH(data: PaymentData(pubkey: bip32.publicKey), network: network);
     return HDWallet(bip32: bip32, p2pkh: p2pkh, network: network);
   }
 
-  factory HDWallet.fromSeed(Uint8List seed, {NetworkType network}) {
+  factory HDWallet.fromSeed(Uint8List seed, {NetworkType? network}) {
     network = network ?? bitcoin;
     final seedHex = HEX.encode(seed);
     final wallet = bip32.BIP32.fromSeed(
-        seed,
-        bip32.NetworkType(
-            bip32: bip32.Bip32Type(
-                public: network.bip32.public, private: network.bip32.private),
-            wif: network.wif));
-    final p2pkh = new P2PKH(
-        data: new PaymentData(pubkey: wallet.publicKey), network: network);
-    return HDWallet(
-        bip32: wallet, p2pkh: p2pkh, network: network, seed: seedHex);
+        seed, bip32.NetworkType(bip32: bip32.Bip32Type(public: network.bip32.public, private: network.bip32.private), wif: network.wif));
+    final p2pkh = P2PKH(data: PaymentData(pubkey: wallet.publicKey), network: network);
+    return HDWallet(bip32: wallet, p2pkh: p2pkh, network: network, seed: seedHex);
   }
 
-  factory HDWallet.fromBase58(String xpub, {NetworkType network}) {
+  factory HDWallet.fromBase58(String xpub, {NetworkType? network}) {
     network = network ?? bitcoin;
     final wallet = bip32.BIP32.fromBase58(
-        xpub,
-        bip32.NetworkType(
-            bip32: bip32.Bip32Type(
-                public: network.bip32.public, private: network.bip32.private),
-            wif: network.wif));
-    final p2pkh = new P2PKH(
-        data: new PaymentData(pubkey: wallet.publicKey), network: network);
+        xpub, bip32.NetworkType(bip32: bip32.Bip32Type(public: network.bip32.public, private: network.bip32.private), wif: network.wif));
+    final p2pkh = P2PKH(data: PaymentData(pubkey: wallet.publicKey), network: network);
     return HDWallet(bip32: wallet, p2pkh: p2pkh, network: network, seed: null);
   }
 
   Uint8List sign(String message) {
     Uint8List messageHash = magicHash(message, network);
-    return _bip32.sign(messageHash);
+    return _bip32!.sign(messageHash);
   }
 
-  bool verify({String message, Uint8List signature}) {
+  bool verify({required String message, required Uint8List signature}) {
     Uint8List messageHash = magicHash(message);
-    return _bip32.verify(messageHash, signature);
+    return _bip32!.verify(messageHash, signature);
   }
 }
 
 class Wallet {
   ECPair _keyPair;
-  P2PKH _p2pkh;
+  P2PKH? _p2pkh;
 
-  String get privKey =>
-      _keyPair != null ? HEX.encode(_keyPair.privateKey) : null;
+  String? get privKey => _keyPair.privateKey != null ? HEX.encode(_keyPair.privateKey!) : null;
 
-  String get pubKey => _keyPair != null ? HEX.encode(_keyPair.publicKey) : null;
+  String? get pubKey => HEX.encode(_keyPair.publicKey);
 
-  String get wif => _keyPair != null ? _keyPair.toWIF() : null;
+  String? get wif => _keyPair.toWIF();
 
-  String get address => _p2pkh != null ? _p2pkh.data.address : null;
+  String? get address => _p2pkh != null ? _p2pkh!.data.address : null;
 
   NetworkType network;
 
   Wallet(this._keyPair, this._p2pkh, this.network);
 
-  factory Wallet.random([NetworkType network]) {
+  factory Wallet.random(NetworkType network) {
     final _keyPair = ECPair.makeRandom(network: network);
-    final _p2pkh = new P2PKH(
-        data: new PaymentData(pubkey: _keyPair.publicKey), network: network);
+    final _p2pkh = P2PKH(data: PaymentData(pubkey: _keyPair.publicKey), network: network);
     return Wallet(_keyPair, _p2pkh, network);
   }
 
-  factory Wallet.fromWIF(String wif, [NetworkType network]) {
+  factory Wallet.fromWIF(String wif, [NetworkType? network]) {
     network = network ?? bitcoin;
     final _keyPair = ECPair.fromWIF(wif, network: network);
-    final _p2pkh = new P2PKH(
-        data: new PaymentData(pubkey: _keyPair.publicKey), network: network);
+    final _p2pkh = P2PKH(data: PaymentData(pubkey: _keyPair.publicKey), network: network);
     return Wallet(_keyPair, _p2pkh, network);
   }
 
@@ -146,7 +130,7 @@ class Wallet {
     return _keyPair.sign(messageHash);
   }
 
-  bool verify({String message, Uint8List signature}) {
+  bool verify({required String message, required Uint8List signature}) {
     Uint8List messageHash = magicHash(message, network);
     return _keyPair.verify(messageHash, signature);
   }
diff --git a/lib/src/classify.dart b/lib/src/classify.dart
index 9af1b34..754457d 100644
--- a/lib/src/classify.dart
+++ b/lib/src/classify.dart
@@ -16,7 +16,7 @@ const SCRIPT_TYPES = {
   'WITNESS_COMMITMENT': 'witnesscommitment'
 };
 
-String classifyOutput(Uint8List script) {
+String? classifyOutput(Uint8List script) {
   if (witnessPubKeyHash.outputCheck(script)) return SCRIPT_TYPES['P2WPKH'];
   if (pubkeyhash.outputCheck(script)) return SCRIPT_TYPES['P2PKH'];
   final chunks = bscript.decompile(script);
@@ -27,14 +27,14 @@ String classifyOutput(Uint8List script) {
 String classifyInput(Uint8List script) {
   final chunks = bscript.decompile(script);
   if (chunks == null) throw new ArgumentError('Invalid script');
-  if (pubkeyhash.inputCheck(chunks)) return SCRIPT_TYPES['P2PKH'];
-  if (pubkey.inputCheck(chunks)) return SCRIPT_TYPES['P2PK'];
-  return SCRIPT_TYPES['NONSTANDARD'];
+  if (pubkeyhash.inputCheck(chunks)) return SCRIPT_TYPES['P2PKH']!;
+  if (pubkey.inputCheck(chunks)) return SCRIPT_TYPES['P2PK']!;
+  return SCRIPT_TYPES['NONSTANDARD']!;
 }
 
 String classifyWitness(List<Uint8List> script) {
   final chunks = bscript.decompile(script);
   if (chunks == null) throw new ArgumentError('Invalid script');
-  if (witnessPubKeyHash.inputCheck(chunks)) return SCRIPT_TYPES['P2WPKH'];
-  return SCRIPT_TYPES['NONSTANDARD'];
+  if (witnessPubKeyHash.inputCheck(chunks)) return SCRIPT_TYPES['P2WPKH']!;
+  return SCRIPT_TYPES['NONSTANDARD']!;
 }
diff --git a/lib/src/ecpair.dart b/lib/src/ecpair.dart
index fc8ce89..d1e0ebf 100644
--- a/lib/src/ecpair.dart
+++ b/lib/src/ecpair.dart
@@ -5,39 +5,38 @@ import 'package:bip32/src/utils/wif.dart' as wif;
 import 'models/networks.dart';
 
 class ECPair {
-  Uint8List _d;
-  Uint8List _Q;
-  NetworkType network;
-  bool compressed;
-  ECPair(Uint8List _d, Uint8List _Q, {network, compressed}) {
+  late Uint8List? _d;
+  late Uint8List? _Q;
+  late NetworkType network;
+  late bool compressed;
+  ECPair(Uint8List? _d, Uint8List? _Q, {network, compressed}) {
     this._d = _d;
     this._Q = _Q;
     this.network = network ?? bitcoin;
     this.compressed = compressed ?? true;
   }
   Uint8List get publicKey {
-    if (_Q == null) _Q = ecc.pointFromScalar(_d, compressed);
-    return _Q;
+    if (_Q == null) _Q = ecc.pointFromScalar(_d!, compressed);
+    return _Q!;
   }
 
-  Uint8List get privateKey => _d;
+  Uint8List? get privateKey => _d;
   String toWIF() {
     if (privateKey == null) {
       throw new ArgumentError('Missing private key');
     }
-    return wif.encode(new wif.WIF(
-        version: network.wif, privateKey: privateKey, compressed: compressed));
+    return wif.encode(new wif.WIF(version: network.wif, privateKey: privateKey!, compressed: compressed));
   }
 
   Uint8List sign(Uint8List hash) {
-    return ecc.sign(hash, privateKey);
+    return ecc.sign(hash, privateKey!);
   }
 
   bool verify(Uint8List hash, Uint8List signature) {
     return ecc.verify(hash, publicKey, signature);
   }
 
-  factory ECPair.fromWIF(String w, {NetworkType network}) {
+  factory ECPair.fromWIF(String w, {NetworkType? network}) {
     wif.WIF decoded = wif.decode(w);
     final version = decoded.version;
     // TODO support multi networks
@@ -54,29 +53,20 @@ class ECPair {
         throw new ArgumentError('Unknown network version');
       }
     }
-    return ECPair.fromPrivateKey(decoded.privateKey,
-        compressed: decoded.compressed, network: nw);
+    return ECPair.fromPrivateKey(decoded.privateKey, compressed: decoded.compressed, network: nw);
   }
-  factory ECPair.fromPublicKey(Uint8List publicKey,
-      {NetworkType network, bool compressed}) {
+  factory ECPair.fromPublicKey(Uint8List publicKey, {NetworkType? network, bool? compressed}) {
     if (!ecc.isPoint(publicKey)) {
-      throw new ArgumentError('Point is not on the curve');
+      throw ArgumentError('Point is not on the curve');
     }
-    return new ECPair(null, publicKey,
-        network: network, compressed: compressed);
+    return ECPair(null, publicKey, network: network, compressed: compressed);
   }
-  factory ECPair.fromPrivateKey(Uint8List privateKey,
-      {NetworkType network, bool compressed}) {
-    if (privateKey.length != 32)
-      throw new ArgumentError(
-          'Expected property privateKey of type Buffer(Length: 32)');
-    if (!ecc.isPrivate(privateKey))
-      throw new ArgumentError('Private key not in range [1, n)');
-    return new ECPair(privateKey, null,
-        network: network, compressed: compressed);
+  factory ECPair.fromPrivateKey(Uint8List privateKey, {NetworkType? network, bool? compressed}) {
+    if (privateKey.length != 32) throw new ArgumentError('Expected property privateKey of type Buffer(Length: 32)');
+    if (!ecc.isPrivate(privateKey)) throw new ArgumentError('Private key not in range [1, n)');
+    return new ECPair(privateKey, null, network: network, compressed: compressed);
   }
-  factory ECPair.makeRandom(
-      {NetworkType network, bool compressed, Function rng}) {
+  factory ECPair.makeRandom({NetworkType? network, bool? compressed, Function? rng}) {
     final rfunc = rng ?? _randomBytes;
     Uint8List d;
 //    int beginTime = DateTime.now().millisecondsSinceEpoch;
diff --git a/lib/src/models/networks.dart b/lib/src/models/networks.dart
index dc4771d..6f5c335 100644
--- a/lib/src/models/networks.dart
+++ b/lib/src/models/networks.dart
@@ -1,20 +1,19 @@
-import 'package:meta/meta.dart';
 
 class NetworkType {
   String messagePrefix;
-  String bech32;
+  String? bech32;
   Bip32Type bip32;
   int pubKeyHash;
   int scriptHash;
   int wif;
 
   NetworkType(
-      {@required this.messagePrefix,
+      {required this.messagePrefix,
       this.bech32,
-      @required this.bip32,
-      @required this.pubKeyHash,
-      @required this.scriptHash,
-      @required this.wif});
+      required this.bip32,
+      required this.pubKeyHash,
+      required this.scriptHash,
+      required this.wif});
 
   @override
   String toString() {
@@ -26,7 +25,7 @@ class Bip32Type {
   int public;
   int private;
 
-  Bip32Type({@required this.public, @required this.private});
+  Bip32Type({required this.public, required this.private});
 
   @override
   String toString() {
diff --git a/lib/src/payments/index.dart b/lib/src/payments/index.dart
index b2b3ed9..1770d8b 100644
--- a/lib/src/payments/index.dart
+++ b/lib/src/payments/index.dart
@@ -1,22 +1,23 @@
 import 'dart:typed_data';
 
 class PaymentData {
-  String address;
-  Uint8List hash;
-  Uint8List output;
-  Uint8List signature;
-  Uint8List pubkey;
-  Uint8List input;
-  List<Uint8List> witness;
+  String? address;
+  Uint8List? hash;
+  Uint8List? output;
+  Uint8List? signature;
+  Uint8List? pubkey;
+  Uint8List? input;
+  List<Uint8List>? witness;
 
-  PaymentData(
-      {this.address,
-      this.hash,
-      this.output,
-      this.pubkey,
-      this.input,
-      this.signature,
-      this.witness});
+  PaymentData({
+    this.address,
+    this.hash,
+    this.output,
+    this.pubkey,
+    this.input,
+    this.signature,
+    this.witness,
+  });
 
   @override
   String toString() {
diff --git a/lib/src/payments/p2pk.dart b/lib/src/payments/p2pk.dart
index 796d6dd..f1eacfc 100644
--- a/lib/src/payments/p2pk.dart
+++ b/lib/src/payments/p2pk.dart
@@ -1,28 +1,23 @@
-import 'dart:typed_data';
-import 'package:meta/meta.dart';
+
 import 'package:bip32/src/utils/ecurve.dart' show isPoint;
-import 'package:bs58check/bs58check.dart' as bs58check;
 
-import '../crypto.dart';
 import '../models/networks.dart';
 import '../payments/index.dart' show PaymentData;
-import '../utils/script.dart' as bscript;
 import '../utils/constants/op.dart';
 
 class P2PK {
-  PaymentData data;
-  NetworkType network;
-  P2PK({@required data, network}) {
+  final PaymentData data;
+  late NetworkType network;
+  P2PK({required this.data, NetworkType? network}) {
     this.network = network ?? bitcoin;
-    this.data = data;
     _init();
   }
 
   _init() {
     if (data.output != null) {
-      if (data.output[data.output.length - 1] != OPS['OP_CHECKSIG'])
+      if (data.output![data.output!.length - 1] != OPS['OP_CHECKSIG'])
         throw new ArgumentError('Output is invalid');
-      if (!isPoint(data.output.sublist(1, -1)))
+      if (!isPoint(data.output!.sublist(1, -1)))
         throw new ArgumentError('Output pubkey is invalid');
     }
     if (data.input != null) {
diff --git a/lib/src/payments/p2pkh.dart b/lib/src/payments/p2pkh.dart
index 60e5bfd..cab00db 100644
--- a/lib/src/payments/p2pkh.dart
+++ b/lib/src/payments/p2pkh.dart
@@ -1,92 +1,76 @@
 import 'dart:typed_data';
-import 'package:meta/meta.dart';
+
 import 'package:bip32/src/utils/ecurve.dart' show isPoint;
 import 'package:bs58check/bs58check.dart' as bs58check;
 
 import '../crypto.dart';
 import '../models/networks.dart';
 import '../payments/index.dart' show PaymentData;
-import '../utils/script.dart' as bscript;
 import '../utils/constants/op.dart';
+import '../utils/script.dart' as bscript;
 
 class P2PKH {
   PaymentData data;
-  NetworkType network;
-  P2PKH({@required data, network}) {
+  NetworkType? network;
+  P2PKH({required this.data, network}) {
     this.network = network ?? bitcoin;
-    this.data = data;
     _init();
   }
   _init() {
     if (data.address != null) {
-      _getDataFromAddress(data.address);
+      _getDataFromAddress(data.address!);
       _getDataFromHash();
     } else if (data.hash != null) {
       _getDataFromHash();
     } else if (data.output != null) {
-      if (!isValidOutput(data.output))
-        throw new ArgumentError('Output is invalid');
-      data.hash = data.output.sublist(3, 23);
+      if (!isValidOutput(data.output!)) throw new ArgumentError('Output is invalid');
+      data.hash = data.output!.sublist(3, 23);
       _getDataFromHash();
     } else if (data.pubkey != null) {
-      data.hash = hash160(data.pubkey);
+      data.hash = hash160(data.pubkey!);
       _getDataFromHash();
       _getDataFromChunk();
     } else if (data.input != null) {
-      List<dynamic> _chunks = bscript.decompile(data.input);
+      List<dynamic> _chunks = bscript.decompile(data.input!)!;
       _getDataFromChunk(_chunks);
       if (_chunks.length != 2) throw new ArgumentError('Input is invalid');
-      if (!bscript.isCanonicalScriptSignature(_chunks[0]))
-        throw new ArgumentError('Input has invalid signature');
-      if (!isPoint(_chunks[1]))
-        throw new ArgumentError('Input has invalid pubkey');
+      if (!bscript.isCanonicalScriptSignature(_chunks[0])) throw new ArgumentError('Input has invalid signature');
+      if (!isPoint(_chunks[1])) throw new ArgumentError('Input has invalid pubkey');
     } else {
       throw new ArgumentError('Not enough data');
     }
   }
 
-  void _getDataFromChunk([List<dynamic> _chunks]) {
+  void _getDataFromChunk([List<dynamic>? _chunks]) {
     if (data.pubkey == null && _chunks != null) {
-      data.pubkey = (_chunks[1] is int)
-          ? new Uint8List.fromList([_chunks[1]])
-          : _chunks[1];
-      data.hash = hash160(data.pubkey);
+      data.pubkey = (_chunks[1] is int) ? Uint8List.fromList([_chunks[1]]) : _chunks[1];
+      data.hash = hash160(data.pubkey!);
       _getDataFromHash();
     }
-    if (data.signature == null && _chunks != null)
-      data.signature = (_chunks[0] is int)
-          ? new Uint8List.fromList([_chunks[0]])
-          : _chunks[0];
+    if (data.signature == null && _chunks != null) data.signature = (_chunks[0] is int) ? new Uint8List.fromList([_chunks[0]]) : _chunks[0];
     if (data.input == null && data.pubkey != null && data.signature != null) {
       data.input = bscript.compile([data.signature, data.pubkey]);
     }
   }
 
   void _getDataFromHash() {
-    if (data.address == null) {
+    if (data.address == null && network?.pubKeyHash != null && data.hash != null) {
       final payload = new Uint8List(21);
-      payload.buffer.asByteData().setUint8(0, network.pubKeyHash);
-      payload.setRange(1, payload.length, data.hash);
+      payload.buffer.asByteData().setUint8(0, network!.pubKeyHash);
+      payload.setRange(1, payload.length, data.hash!);
       data.address = bs58check.encode(payload);
     }
     if (data.output == null) {
-      data.output = bscript.compile([
-        OPS['OP_DUP'],
-        OPS['OP_HASH160'],
-        data.hash,
-        OPS['OP_EQUALVERIFY'],
-        OPS['OP_CHECKSIG']
-      ]);
+      data.output = bscript.compile([OPS['OP_DUP'], OPS['OP_HASH160'], data.hash, OPS['OP_EQUALVERIFY'], OPS['OP_CHECKSIG']]);
     }
   }
 
   void _getDataFromAddress(String address) {
     Uint8List payload = bs58check.decode(address);
     final version = payload.buffer.asByteData().getUint8(0);
-    if (version != network.pubKeyHash)
-      throw new ArgumentError('Invalid version or Network mismatch');
+    if (version != network?.pubKeyHash) throw new ArgumentError('Invalid version or Network mismatch');
     data.hash = payload.sublist(1);
-    if (data.hash.length != 20) throw new ArgumentError('Invalid address');
+    if (data.hash?.length != 20) throw new ArgumentError('Invalid address');
   }
 }
 
@@ -100,16 +84,8 @@ isValidOutput(Uint8List data) {
 }
 
 // Backward compatibility
-@Deprecated(
-    "The 'P2PKHData' class is deprecated. Use the 'PaymentData' package instead.")
+@Deprecated("The 'P2PKHData' class is deprecated. Use the 'PaymentData' package instead.")
 class P2PKHData extends PaymentData {
   P2PKHData({address, hash, output, pubkey, input, signature, witness})
-      : super(
-            address: address,
-            hash: hash,
-            output: output,
-            pubkey: pubkey,
-            input: input,
-            signature: signature,
-            witness: witness);
+      : super(address: address, hash: hash, output: output, pubkey: pubkey, input: input, signature: signature, witness: witness);
 }
diff --git a/lib/src/payments/p2wpkh.dart b/lib/src/payments/p2wpkh.dart
index 04cfbe2..d3e6a81 100644
--- a/lib/src/payments/p2wpkh.dart
+++ b/lib/src/payments/p2wpkh.dart
@@ -1,5 +1,4 @@
 import 'dart:typed_data';
-import 'package:meta/meta.dart';
 import 'package:bip32/src/utils/ecurve.dart' show isPoint;
 import 'package:bech32/bech32.dart';
 
@@ -12,23 +11,19 @@ import '../utils/constants/op.dart';
 class P2WPKH {
   final EMPTY_SCRIPT = Uint8List.fromList([]);
 
-  PaymentData data;
-  NetworkType network;
-  P2WPKH({@required data, network}) {
+  final PaymentData data;
+  late NetworkType network;
+  P2WPKH({required this.data, NetworkType? network}) {
     this.network = network ?? bitcoin;
-    this.data = data;
     _init();
   }
 
   _init() {
-    if (data.address == null &&
-        data.hash == null &&
-        data.output == null &&
-        data.pubkey == null &&
-        data.witness == null) throw new ArgumentError('Not enough data');
+    if (data.address == null && data.hash == null && data.output == null && data.pubkey == null && data.witness == null)
+      throw ArgumentError('Not enough data');
 
     if (data.address != null) {
-      _getDataFromAddress(data.address);
+      _getDataFromAddress(data.address!);
     }
 
     if (data.hash != null) {
@@ -36,43 +31,38 @@ class P2WPKH {
     }
 
     if (data.output != null) {
-      if (data.output.length != 22 ||
-          data.output[0] != OPS['OP_0'] ||
-          data.output[1] != 20) // 0x14
-        throw new ArgumentError('Output is invalid');
+      if (data.output!.length != 22 || data.output![0] != OPS['OP_0'] || data.output![1] != 20) // 0x14
+        throw ArgumentError('Output is invalid');
       if (data.hash == null) {
-        data.hash = data.output.sublist(2);
+        data.hash = data.output!.sublist(2);
       }
       _getDataFromHash();
     }
 
     if (data.pubkey != null) {
-      data.hash = hash160(data.pubkey);
+      data.hash = hash160(data.pubkey!);
       _getDataFromHash();
     }
 
     if (data.witness != null) {
-      if (data.witness.length != 2)
-        throw new ArgumentError('Witness is invalid');
-      if (!bscript.isCanonicalScriptSignature(data.witness[0]))
-        throw new ArgumentError('Witness has invalid signature');
-      if (!isPoint(data.witness[1]))
-        throw new ArgumentError('Witness has invalid pubkey');
-      _getDataFromWitness(data.witness);
+      if (data.witness!.length != 2) throw ArgumentError('Witness is invalid');
+      if (!bscript.isCanonicalScriptSignature(data.witness![0])) throw ArgumentError('Witness has invalid signature');
+      if (!isPoint(data.witness![1])) throw ArgumentError('Witness has invalid pubkey');
+      _getDataFromWitness(data.witness!);
     } else if (data.pubkey != null && data.signature != null) {
-      data.witness = [data.signature, data.pubkey];
+      data.witness = [data.signature!, data.pubkey!];
       if (data.input == null) data.input = EMPTY_SCRIPT;
     }
   }
 
-  void _getDataFromWitness([List<Uint8List> witness]) {
+  void _getDataFromWitness(List<Uint8List> witness) {
     if (data.input == null) {
       data.input = EMPTY_SCRIPT;
     }
     if (data.pubkey == null) {
       data.pubkey = witness[1];
       if (data.hash == null) {
-        data.hash = hash160(data.pubkey);
+        data.hash = hash160(data.pubkey!);
       }
       _getDataFromHash();
     }
@@ -80,8 +70,8 @@ class P2WPKH {
   }
 
   void _getDataFromHash() {
-    if (data.address == null) {
-      data.address = segwit.encode(Segwit(network.bech32, 0, data.hash));
+    if (data.address == null && network.bech32 != null && data.hash != null) {
+      data.address = segwit.encode(Segwit(network.bech32!, 0, data.hash!));
     }
     if (data.output == null) {
       data.output = bscript.compile([OPS['OP_0'], data.hash]);
@@ -91,17 +81,16 @@ class P2WPKH {
   void _getDataFromAddress(String address) {
     try {
       Segwit _address = segwit.decode(address);
-      if (network.bech32 != _address.hrp)
-        throw new ArgumentError('Invalid prefix or Network mismatch');
+      if (network.bech32 != _address.hrp) throw ArgumentError('Invalid prefix or Network mismatch');
       if (_address.version != 0) // Only support version 0 now;
-        throw new ArgumentError('Invalid address version');
+        throw ArgumentError('Invalid address version');
       data.hash = Uint8List.fromList(_address.program);
     } on InvalidHrp {
-      throw new ArgumentError('Invalid prefix or Network mismatch');
+      throw ArgumentError('Invalid prefix or Network mismatch');
     } on InvalidProgramLength {
-      throw new ArgumentError('Invalid address data');
+      throw ArgumentError('Invalid address data');
     } on InvalidWitnessVersion {
-      throw new ArgumentError('Invalid witness address version');
+      throw ArgumentError('Invalid witness address version');
     }
   }
 }
diff --git a/lib/src/templates/pubkey.dart b/lib/src/templates/pubkey.dart
index c839e85..ef703de 100644
--- a/lib/src/templates/pubkey.dart
+++ b/lib/src/templates/pubkey.dart
@@ -1,11 +1,10 @@
 import 'dart:typed_data';
 import '../utils/script.dart' as bscript;
-import '../utils/constants/op.dart';
 
 bool inputCheck(List<dynamic> chunks) {
   return chunks.length == 1 && bscript.isCanonicalScriptSignature(chunks[0]);
 }
 
-bool outputCheck(Uint8List script) {
+bool? outputCheck(Uint8List script) {
   // TODO
 }
diff --git a/lib/src/templates/pubkeyhash.dart b/lib/src/templates/pubkeyhash.dart
index 88af094..d60eddf 100644
--- a/lib/src/templates/pubkeyhash.dart
+++ b/lib/src/templates/pubkeyhash.dart
@@ -3,10 +3,7 @@ import '../utils/script.dart' as bscript;
 import '../utils/constants/op.dart';
 
 bool inputCheck(List<dynamic> chunks) {
-  return chunks != null &&
-      chunks.length == 2 &&
-      bscript.isCanonicalScriptSignature(chunks[0]) &&
-      bscript.isCanonicalPubKey(chunks[1]);
+  return chunks.length == 2 && bscript.isCanonicalScriptSignature(chunks[0]) && bscript.isCanonicalPubKey(chunks[1]);
 }
 
 bool outputCheck(Uint8List script) {
diff --git a/lib/src/templates/witnesspubkeyhash.dart b/lib/src/templates/witnesspubkeyhash.dart
index ec660d7..9562edb 100644
--- a/lib/src/templates/witnesspubkeyhash.dart
+++ b/lib/src/templates/witnesspubkeyhash.dart
@@ -3,10 +3,7 @@ import '../utils/script.dart' as bscript;
 import '../utils/constants/op.dart';
 
 bool inputCheck(List<dynamic> chunks) {
-  return chunks != null &&
-      chunks.length == 2 &&
-      bscript.isCanonicalScriptSignature(chunks[0]) &&
-      bscript.isCanonicalPubKey(chunks[1]);
+  return chunks.length == 2 && bscript.isCanonicalScriptSignature(chunks[0]) && bscript.isCanonicalPubKey(chunks[1]);
 }
 
 bool outputCheck(Uint8List script) {
diff --git a/lib/src/transaction.dart b/lib/src/transaction.dart
deleted file mode 100644
index 61f8756..0000000
--- a/lib/src/transaction.dart
+++ /dev/null
@@ -1,719 +0,0 @@
-import 'dart:typed_data';
-import 'package:hex/hex.dart';
-import 'payments/index.dart' show PaymentData;
-import 'payments/p2pkh.dart' show P2PKH;
-import 'payments/p2pk.dart' show P2PK;
-import 'payments/p2wpkh.dart' show P2WPKH;
-import 'crypto.dart' as bcrypto;
-import 'classify.dart';
-import 'utils/check_types.dart';
-import 'utils/script.dart' as bscript;
-import 'utils/constants/op.dart';
-import 'utils/varuint.dart' as varuint;
-
-const DEFAULT_SEQUENCE = 0xffffffff;
-const SIGHASH_ALL = 0x01;
-const SIGHASH_NONE = 0x02;
-const SIGHASH_SINGLE = 0x03;
-const SIGHASH_ANYONECANPAY = 0x80;
-const ADVANCED_TRANSACTION_MARKER = 0x00;
-const ADVANCED_TRANSACTION_FLAG = 0x01;
-final EMPTY_SCRIPT = Uint8List.fromList([]);
-final EMPTY_WITNESS = new List<Uint8List>();
-final ZERO = HEX
-    .decode('0000000000000000000000000000000000000000000000000000000000000000');
-final ONE = HEX
-    .decode('0000000000000000000000000000000000000000000000000000000000000001');
-final VALUE_UINT64_MAX = HEX.decode('ffffffffffffffff');
-final BLANK_OUTPUT =
-    new Output(script: EMPTY_SCRIPT, valueBuffer: VALUE_UINT64_MAX);
-
-class Transaction {
-  int version = 1;
-  int locktime = 0;
-  List<Input> ins = [];
-  List<Output> outs = [];
-  Transaction();
-
-  int addInput(Uint8List hash, int index, [int sequence, Uint8List scriptSig]) {
-    ins.add(new Input(
-        hash: hash,
-        index: index,
-        sequence: sequence ?? DEFAULT_SEQUENCE,
-        script: scriptSig ?? EMPTY_SCRIPT,
-        witness: EMPTY_WITNESS));
-    return ins.length - 1;
-  }
-
-  int addOutput(Uint8List scriptPubKey, int value) {
-    outs.add(new Output(script: scriptPubKey, value: value));
-    return outs.length - 1;
-  }
-
-  bool hasWitnesses() {
-    var witness = ins.firstWhere(
-        (input) => input.witness != null && input.witness.length != 0,
-        orElse: () => null);
-    return witness != null;
-  }
-
-  setInputScript(int index, Uint8List scriptSig) {
-    ins[index].script = scriptSig;
-  }
-
-  setWitness(int index, List<Uint8List> witness) {
-    ins[index].witness = witness;
-  }
-
-  hashForWitnessV0(
-      int inIndex, Uint8List prevOutScript, int value, int hashType) {
-    var tbuffer = Uint8List.fromList([]);
-    var toffset = 0;
-    // Any changes made to the ByteData will also change the buffer, and vice versa.
-    // https://api.dart.dev/stable/2.7.1/dart-typed_data/ByteBuffer/asByteData.html
-    ByteData bytes = tbuffer.buffer.asByteData();
-    var hashOutputs = ZERO;
-    var hashPrevouts = ZERO;
-    var hashSequence = ZERO;
-
-    writeSlice(slice) {
-      tbuffer.setRange(toffset, toffset + slice.length, slice);
-      toffset += slice.length;
-    }
-
-    writeUInt8(i) {
-      bytes.setUint8(toffset, i);
-      toffset++;
-    }
-
-    writeUInt32(i) {
-      bytes.setUint32(toffset, i, Endian.little);
-      toffset += 4;
-    }
-
-    writeInt32(i) {
-      bytes.setInt32(toffset, i, Endian.little);
-      toffset += 4;
-    }
-
-    writeUInt64(i) {
-      bytes.setUint64(toffset, i, Endian.little);
-      toffset += 8;
-    }
-
-    writeVarInt(i) {
-      varuint.encode(i, tbuffer, toffset);
-      toffset += varuint.encodingLength(i);
-    }
-
-    writeVarSlice(slice) {
-      writeVarInt(slice.length);
-      writeSlice(slice);
-    }
-
-    writeVector(vector) {
-      writeVarInt(vector.length);
-      vector.forEach((buf) {
-        writeVarSlice(buf);
-      });
-    }
-
-    if ((hashType & SIGHASH_ANYONECANPAY) == 0) {
-      tbuffer = new Uint8List(36 * this.ins.length);
-      bytes = tbuffer.buffer.asByteData();
-      toffset = 0;
-
-      ins.forEach((txIn) {
-        writeSlice(txIn.hash);
-        writeUInt32(txIn.index);
-      });
-      hashPrevouts = bcrypto.hash256(tbuffer);
-    }
-
-    if ((hashType & SIGHASH_ANYONECANPAY) == 0 &&
-        (hashType & 0x1f) != SIGHASH_SINGLE &&
-        (hashType & 0x1f) != SIGHASH_NONE) {
-      tbuffer = new Uint8List(4 * this.ins.length);
-      bytes = tbuffer.buffer.asByteData();
-      toffset = 0;
-      ins.forEach((txIn) {
-        writeUInt32(txIn.sequence);
-      });
-      hashSequence = bcrypto.hash256(tbuffer);
-    }
-
-    if ((hashType & 0x1f) != SIGHASH_SINGLE &&
-        (hashType & 0x1f) != SIGHASH_NONE) {
-      var txOutsSize =
-          outs.fold(0, (sum, output) => sum + 8 + varSliceSize(output.script));
-      tbuffer = new Uint8List(txOutsSize);
-      bytes = tbuffer.buffer.asByteData();
-      toffset = 0;
-      outs.forEach((txOut) {
-        writeUInt64(txOut.value);
-        writeVarSlice(txOut.script);
-      });
-      hashOutputs = bcrypto.hash256(tbuffer);
-    } else if ((hashType & 0x1f) == SIGHASH_SINGLE && inIndex < outs.length) {
-      // SIGHASH_SINGLE only hash that according output
-      var output = outs[inIndex];
-      tbuffer = new Uint8List(8 + varSliceSize(output.script));
-      bytes = tbuffer.buffer.asByteData();
-      toffset = 0;
-      writeUInt64(output.value);
-      writeVarSlice(output.script);
-      hashOutputs = bcrypto.hash256(tbuffer);
-    }
-
-    tbuffer = new Uint8List(156 + varSliceSize(prevOutScript));
-    bytes = tbuffer.buffer.asByteData();
-    toffset = 0;
-    var input = ins[inIndex];
-    writeUInt32(version);
-    writeSlice(hashPrevouts);
-    writeSlice(hashSequence);
-    writeSlice(input.hash);
-    writeUInt32(input.index);
-    writeVarSlice(prevOutScript);
-    writeUInt64(value);
-    writeUInt32(input.sequence);
-    writeSlice(hashOutputs);
-    writeUInt32(this.locktime);
-    writeUInt32(hashType);
-
-    return bcrypto.hash256(tbuffer);
-  }
-
-  hashForSignature(int inIndex, Uint8List prevOutScript, int hashType) {
-    if (inIndex >= ins.length) return ONE;
-    // ignore OP_CODESEPARATOR
-    final ourScript =
-        bscript.compile(bscript.decompile(prevOutScript).where((x) {
-      return x != OPS['OP_CODESEPARATOR'];
-    }).toList());
-    final txTmp = Transaction.clone(this);
-    // SIGHASH_NONE: ignore all outputs? (wildcard payee)
-    if ((hashType & 0x1f) == SIGHASH_NONE) {
-      txTmp.outs = [];
-      // ignore sequence numbers (except at inIndex)
-      for (var i = 0; i < txTmp.ins.length; i++) {
-        if (i != inIndex) {
-          txTmp.ins[i].sequence = 0;
-        }
-      }
-
-      // SIGHASH_SINGLE: ignore all outputs, except at the same index?
-    } else if ((hashType & 0x1f) == SIGHASH_SINGLE) {
-      // https://github.com/bitcoin/bitcoin/blob/master/src/test/sighash_tests.cpp#L60
-      if (inIndex >= outs.length) return ONE;
-
-      // truncate outputs after
-      txTmp.outs.length = inIndex + 1;
-
-      // 'blank' outputs before
-      for (var i = 0; i < inIndex; i++) {
-        txTmp.outs[i] = BLANK_OUTPUT;
-      }
-      // ignore sequence numbers (except at inIndex)
-      for (var i = 0; i < txTmp.ins.length; i++) {
-        if (i != inIndex) {
-          txTmp.ins[i].sequence = 0;
-        }
-      }
-    }
-
-    // SIGHASH_ANYONECANPAY: ignore inputs entirely?
-    if (hashType & SIGHASH_ANYONECANPAY != 0) {
-      txTmp.ins = [txTmp.ins[inIndex]];
-      txTmp.ins[0].script = ourScript;
-      // SIGHASH_ALL: only ignore input scripts
-    } else {
-      // 'blank' others input scripts
-      txTmp.ins.forEach((input) {
-        input.script = EMPTY_SCRIPT;
-      });
-      txTmp.ins[inIndex].script = ourScript;
-    }
-    // serialize and hash
-    final buffer = Uint8List(txTmp.virtualSize() + 4);
-    buffer.buffer
-        .asByteData()
-        .setUint32(buffer.length - 4, hashType, Endian.little);
-    txTmp._toBuffer(buffer, 0);
-    return bcrypto.hash256(buffer);
-  }
-
-  _byteLength(_ALLOW_WITNESS) {
-    var hasWitness = _ALLOW_WITNESS && hasWitnesses();
-    return (hasWitness ? 10 : 8) +
-        varuint.encodingLength(ins.length) +
-        varuint.encodingLength(outs.length) +
-        ins.fold(0, (sum, input) => sum + 40 + varSliceSize(input.script)) +
-        outs.fold(0, (sum, output) => sum + 8 + varSliceSize(output.script)) +
-        (hasWitness
-            ? ins.fold(0, (sum, input) => sum + vectorSize(input.witness))
-            : 0);
-  }
-
-  int vectorSize(List<Uint8List> someVector) {
-    var length = someVector.length;
-    return varuint.encodingLength(length) +
-        someVector.fold(0, (sum, witness) => sum + varSliceSize(witness));
-  }
-
-  int weight() {
-    var base = _byteLength(false);
-    var total = _byteLength(true);
-    return base * 3 + total;
-  }
-
-  int byteLength() {
-    return _byteLength(true);
-  }
-
-  int virtualSize() {
-    return (weight() / 4).ceil();
-  }
-
-  Uint8List toBuffer([Uint8List buffer, int initialOffset]) {
-    return this._toBuffer(buffer, initialOffset, true);
-  }
-
-  String toHex() {
-    return HEX.encode(this.toBuffer());
-  }
-
-  bool isCoinbaseHash(buffer) {
-    isHash256bit(buffer);
-    for (var i = 0; i < 32; ++i) {
-      if (buffer[i] != 0) return false;
-    }
-    return true;
-  }
-
-  bool isCoinbase() {
-    return ins.length == 1 && isCoinbaseHash(ins[0].hash);
-  }
-
-  Uint8List getHash() {
-    // if (isCoinbase()) return Uint8List.fromList(List.generate(32, (i) => 0));
-    return bcrypto.hash256(_toBuffer(null, null, false));
-  }
-
-  String getId() {
-    return HEX.encode(getHash().reversed.toList());
-  }
-
-  _toBuffer([Uint8List buffer, initialOffset, bool _ALLOW_WITNESS = false]) {
-    // _ALLOW_WITNESS is used to separate witness part when calculating tx id
-    if (buffer == null) buffer = new Uint8List(_byteLength(_ALLOW_WITNESS));
-
-    // Any changes made to the ByteData will also change the buffer, and vice versa.
-    // https://api.dart.dev/stable/2.7.1/dart-typed_data/ByteBuffer/asByteData.html
-    var bytes = buffer.buffer.asByteData();
-    var offset = initialOffset ?? 0;
-
-    writeSlice(slice) {
-      buffer.setRange(offset, offset + slice.length, slice);
-      offset += slice.length;
-    }
-
-    writeUInt8(i) {
-      bytes.setUint8(offset, i);
-      offset++;
-    }
-
-    writeUInt32(i) {
-      bytes.setUint32(offset, i, Endian.little);
-      offset += 4;
-    }
-
-    writeInt32(i) {
-      bytes.setInt32(offset, i, Endian.little);
-      offset += 4;
-    }
-
-    writeUInt64(i) {
-      bytes.setUint64(offset, i, Endian.little);
-      offset += 8;
-    }
-
-    writeVarInt(i) {
-      varuint.encode(i, buffer, offset);
-      offset += varuint.encodingLength(i);
-    }
-
-    writeVarSlice(slice) {
-      writeVarInt(slice.length);
-      writeSlice(slice);
-    }
-
-    writeVector(vector) {
-      writeVarInt(vector.length);
-      vector.forEach((buf) {
-        writeVarSlice(buf);
-      });
-    }
-
-    // Start writeBuffer
-    writeInt32(version);
-
-    if (_ALLOW_WITNESS && hasWitnesses()) {
-      writeUInt8(ADVANCED_TRANSACTION_MARKER);
-      writeUInt8(ADVANCED_TRANSACTION_FLAG);
-    }
-
-    writeVarInt(this.ins.length);
-
-    ins.forEach((txIn) {
-      writeSlice(txIn.hash);
-      writeUInt32(txIn.index);
-      writeVarSlice(txIn.script);
-      writeUInt32(txIn.sequence);
-    });
-
-    writeVarInt(this.outs.length);
-
-    outs.forEach((txOut) {
-      if (txOut.valueBuffer == null) {
-        writeUInt64(txOut.value);
-      } else {
-        writeSlice(txOut.valueBuffer);
-      }
-      writeVarSlice(txOut.script);
-    });
-
-    if (_ALLOW_WITNESS && hasWitnesses()) {
-      ins.forEach((txInt) {
-        writeVector(txInt.witness);
-      });
-    }
-
-    writeUInt32(this.locktime);
-    // End writeBuffer
-
-    // avoid slicing unless necessary
-    if (initialOffset != null) return buffer.sublist(initialOffset, offset);
-
-    return buffer;
-  }
-
-  factory Transaction.clone(Transaction _tx) {
-    Transaction tx = new Transaction();
-    tx.version = _tx.version;
-    tx.locktime = _tx.locktime;
-    tx.ins = _tx.ins.map((input) {
-      return Input.clone(input);
-    }).toList();
-    tx.outs = _tx.outs.map((output) {
-      return Output.clone(output);
-    }).toList();
-    return tx;
-  }
-
-  factory Transaction.fromBuffer(
-    Uint8List buffer, {
-    bool noStrict = false,
-  }) {
-    var offset = 0;
-    // Any changes made to the ByteData will also change the buffer, and vice versa.
-    // https://api.dart.dev/stable/2.7.1/dart-typed_data/ByteBuffer/asByteData.html
-    ByteData bytes = buffer.buffer.asByteData();
-
-    int readUInt8() {
-      final i = bytes.getUint8(offset);
-      offset++;
-      return i;
-    }
-
-    int readUInt32() {
-      final i = bytes.getUint32(offset, Endian.little);
-      offset += 4;
-      return i;
-    }
-
-    int readInt32() {
-      final i = bytes.getInt32(offset, Endian.little);
-      offset += 4;
-      return i;
-    }
-
-    int readUInt64() {
-      final i = bytes.getUint64(offset, Endian.little);
-      offset += 8;
-      return i;
-    }
-
-    Uint8List readSlice(n) {
-      offset += n;
-      return buffer.sublist(offset - n, offset);
-    }
-
-    int readVarInt() {
-      final vi = varuint.decode(buffer, offset);
-      offset += varuint.encodingLength(vi);
-      return vi;
-    }
-
-    Uint8List readVarSlice() {
-      return readSlice(readVarInt());
-    }
-
-    List<Uint8List> readVector() {
-      var count = readVarInt();
-      List<Uint8List> vector = [];
-      for (var i = 0; i < count; ++i) {
-        vector.add(readVarSlice());
-      }
-      return vector;
-    }
-
-    final tx = new Transaction();
-    tx.version = readInt32();
-
-    final marker = readUInt8();
-    final flag = readUInt8();
-
-    var hasWitnesses = false;
-    if (marker == ADVANCED_TRANSACTION_MARKER &&
-        flag == ADVANCED_TRANSACTION_FLAG) {
-      hasWitnesses = true;
-    } else {
-      offset -= 2; // Reset offset if not segwit tx
-    }
-
-    final vinLen = readVarInt();
-    for (var i = 0; i < vinLen; ++i) {
-      tx.ins.add(new Input(
-          hash: readSlice(32),
-          index: readUInt32(),
-          script: readVarSlice(),
-          sequence: readUInt32()));
-    }
-
-    final voutLen = readVarInt();
-    for (var i = 0; i < voutLen; ++i) {
-      tx.outs.add(new Output(value: readUInt64(), script: readVarSlice()));
-    }
-
-    if (hasWitnesses) {
-      for (var i = 0; i < vinLen; ++i) {
-        tx.ins[i].witness = readVector();
-      }
-    }
-
-    tx.locktime = readUInt32();
-
-    if (noStrict) return tx;
-
-    if (offset != buffer.length)
-      throw new ArgumentError('Transaction has unexpected data');
-
-    return tx;
-  }
-
-  factory Transaction.fromHex(
-    String hex, {
-    bool noStrict = false,
-  }) {
-    return Transaction.fromBuffer(
-      HEX.decode(hex),
-      noStrict: noStrict,
-    );
-  }
-
-  @override
-  String toString() {
-    this.ins.forEach((txInput) {
-      print(txInput.toString());
-    });
-    this.outs.forEach((txOutput) {
-      print(txOutput.toString());
-    });
-  }
-}
-
-class Input {
-  Uint8List hash;
-  int index;
-  int sequence;
-  int value;
-  Uint8List script;
-  Uint8List signScript;
-  Uint8List prevOutScript;
-  String prevOutType;
-  bool hasWitness;
-  List<Uint8List> pubkeys;
-  List<Uint8List> signatures;
-  List<Uint8List> witness;
-
-  Input(
-      {this.hash,
-      this.index,
-      this.script,
-      this.sequence,
-      this.value,
-      this.prevOutScript,
-      this.pubkeys,
-      this.signatures,
-      this.witness,
-      this.prevOutType}) {
-    this.hasWitness = false; // Default value
-    if (this.hash != null && !isHash256bit(this.hash))
-      throw new ArgumentError('Invalid input hash');
-    if (this.index != null && !isUint(this.index, 32))
-      throw new ArgumentError('Invalid input index');
-    if (this.sequence != null && !isUint(this.sequence, 32))
-      throw new ArgumentError('Invalid input sequence');
-    if (this.value != null && !isShatoshi(this.value))
-      throw ArgumentError('Invalid ouput value');
-  }
-
-  factory Input.expandInput(Uint8List scriptSig, List<Uint8List> witness,
-      [String type, Uint8List scriptPubKey]) {
-    if (type == null || type == '') {
-      var ssType = classifyInput(scriptSig);
-      var wsType = classifyWitness(witness);
-      if (ssType == SCRIPT_TYPES['NONSTANDARD']) ssType = null;
-      if (wsType == SCRIPT_TYPES['NONSTANDARD']) wsType = null;
-      type = ssType ?? wsType;
-    }
-    if (type == SCRIPT_TYPES['P2WPKH']) {
-      P2WPKH p2wpkh = new P2WPKH(data: new PaymentData(witness: witness));
-      return new Input(
-          prevOutScript: p2wpkh.data.output,
-          prevOutType: SCRIPT_TYPES['P2WPKH'],
-          pubkeys: [p2wpkh.data.pubkey],
-          signatures: [p2wpkh.data.signature]);
-    } else if (type == SCRIPT_TYPES['P2PKH']) {
-      P2PKH p2pkh = new P2PKH(data: new PaymentData(input: scriptSig));
-      return new Input(
-          prevOutScript: p2pkh.data.output,
-          prevOutType: SCRIPT_TYPES['P2PKH'],
-          pubkeys: [p2pkh.data.pubkey],
-          signatures: [p2pkh.data.signature]);
-    } else if (type == SCRIPT_TYPES['P2PK']) {
-      P2PK p2pk = new P2PK(data: new PaymentData(input: scriptSig));
-      return new Input(
-          prevOutType: SCRIPT_TYPES['P2PK'],
-          pubkeys: [],
-          signatures: [p2pk.data.signature]);
-    }
-  }
-
-  factory Input.clone(Input input) {
-    return new Input(
-      hash: input.hash != null ? Uint8List.fromList(input.hash) : null,
-      index: input.index,
-      script: input.script != null ? Uint8List.fromList(input.script) : null,
-      sequence: input.sequence,
-      value: input.value,
-      prevOutScript: input.prevOutScript != null
-          ? Uint8List.fromList(input.prevOutScript)
-          : null,
-      pubkeys: input.pubkeys != null
-          ? input.pubkeys.map(
-              (pubkey) => pubkey != null ? Uint8List.fromList(pubkey) : null)
-          : null,
-      signatures: input.signatures != null
-          ? input.signatures.map((signature) =>
-              signature != null ? Uint8List.fromList(signature) : null)
-          : null,
-    );
-  }
-
-  @override
-  String toString() {
-    return 'Input{hash: $hash, index: $index, sequence: $sequence, value: $value, script: $script, signScript: $signScript, prevOutScript: $prevOutScript, pubkeys: $pubkeys, signatures: $signatures, witness: $witness, prevOutType: $prevOutType}';
-  }
-}
-
-class Output {
-  Uint8List script;
-  int value;
-  Uint8List valueBuffer;
-  List<Uint8List> pubkeys;
-  List<Uint8List> signatures;
-
-  Output(
-      {this.script,
-      this.value,
-      this.pubkeys,
-      this.signatures,
-      this.valueBuffer}) {
-    if (value != null && !isShatoshi(value))
-      throw ArgumentError('Invalid ouput value');
-  }
-
-  factory Output.expandOutput(Uint8List script, [Uint8List ourPubKey]) {
-    if (ourPubKey == null) return new Output();
-    var type = classifyOutput(script);
-    if (type == SCRIPT_TYPES['P2WPKH']) {
-      Uint8List wpkh1 =
-          new P2WPKH(data: new PaymentData(output: script)).data.hash;
-      Uint8List wpkh2 = bcrypto.hash160(ourPubKey);
-      if (wpkh1 != wpkh2) throw ArgumentError('Hash mismatch!');
-      return new Output(pubkeys: [ourPubKey], signatures: [null]);
-    } else if (type == SCRIPT_TYPES['P2PKH']) {
-      Uint8List pkh1 =
-          new P2PKH(data: new PaymentData(output: script)).data.hash;
-      Uint8List pkh2 = bcrypto.hash160(ourPubKey);
-      if (pkh1 != pkh2) throw ArgumentError('Hash mismatch!');
-      return new Output(pubkeys: [ourPubKey], signatures: [null]);
-    }
-  }
-
-  factory Output.clone(Output output) {
-    return new Output(
-      script: output.script != null ? Uint8List.fromList(output.script) : null,
-      value: output.value,
-      valueBuffer: output.valueBuffer != null
-          ? Uint8List.fromList(output.valueBuffer)
-          : null,
-      pubkeys: output.pubkeys != null
-          ? output.pubkeys.map(
-              (pubkey) => pubkey != null ? Uint8List.fromList(pubkey) : null)
-          : null,
-      signatures: output.signatures != null
-          ? output.signatures.map((signature) =>
-              signature != null ? Uint8List.fromList(signature) : null)
-          : null,
-    );
-  }
-
-  @override
-  String toString() {
-    return 'Output{script: $script, value: $value, valueBuffer: $valueBuffer, pubkeys: $pubkeys, signatures: $signatures}';
-  }
-}
-
-bool isCoinbaseHash(Uint8List buffer) {
-  if (!isHash256bit(buffer)) throw new ArgumentError('Invalid hash');
-  for (var i = 0; i < 32; ++i) {
-    if (buffer[i] != 0) return false;
-  }
-  return true;
-}
-
-bool _isP2PKHInput(script) {
-  final chunks = bscript.decompile(script);
-  return chunks != null &&
-      chunks.length == 2 &&
-      bscript.isCanonicalScriptSignature(chunks[0]) &&
-      bscript.isCanonicalPubKey(chunks[1]);
-}
-
-bool _isP2PKHOutput(script) {
-  final buffer = bscript.compile(script);
-  return buffer.length == 25 &&
-      buffer[0] == OPS['OP_DUP'] &&
-      buffer[1] == OPS['OP_HASH160'] &&
-      buffer[2] == 0x14 &&
-      buffer[23] == OPS['OP_EQUALVERIFY'] &&
-      buffer[24] == OPS['OP_CHECKSIG'];
-}
-
-int varSliceSize(Uint8List someScript) {
-  final length = someScript.length;
-  return varuint.encodingLength(length) + length;
-}
diff --git a/lib/src/transaction_builder.dart b/lib/src/transaction_builder.dart
deleted file mode 100644
index 2ff61bf..0000000
--- a/lib/src/transaction_builder.dart
+++ /dev/null
@@ -1,377 +0,0 @@
-import 'dart:typed_data';
-import 'package:meta/meta.dart';
-import 'package:hex/hex.dart';
-import 'package:bs58check/bs58check.dart' as bs58check;
-import 'package:bech32/bech32.dart';
-import 'utils/script.dart' as bscript;
-import 'ecpair.dart';
-import 'models/networks.dart';
-import 'transaction.dart';
-import 'address.dart';
-import 'payments/index.dart' show PaymentData;
-import 'payments/p2pkh.dart';
-import 'payments/p2wpkh.dart';
-import 'classify.dart';
-
-class TransactionBuilder {
-  NetworkType network;
-  int maximumFeeRate;
-  List<Input> _inputs;
-  Transaction _tx;
-  Map _prevTxSet = {};
-
-  TransactionBuilder({NetworkType network, int maximumFeeRate}) {
-    this.network = network ?? bitcoin;
-    this.maximumFeeRate = maximumFeeRate ?? 2500;
-    this._inputs = [];
-    this._tx = new Transaction();
-    this._tx.version = 2;
-  }
-
-  List<Input> get inputs => _inputs;
-
-  factory TransactionBuilder.fromTransaction(Transaction transaction,
-      [NetworkType network]) {
-    final txb = new TransactionBuilder(network: network);
-    // Copy transaction fields
-    txb.setVersion(transaction.version);
-    txb.setLockTime(transaction.locktime);
-
-    // Copy outputs (done first to avoid signature invalidation)
-    transaction.outs.forEach((txOut) {
-      txb.addOutput(txOut.script, txOut.value);
-    });
-
-    transaction.ins.forEach((txIn) {
-      txb._addInputUnsafe(
-          txIn.hash,
-          txIn.index,
-          new Input(
-              sequence: txIn.sequence,
-              script: txIn.script,
-              witness: txIn.witness));
-    });
-
-    // fix some things not possible through the public API
-    // print(txb.toString());
-    // txb.__INPUTS.forEach((input, i) => {
-    //   fixMultisigOrder(input, transaction, i);
-    // });
-
-    return txb;
-  }
-
-  setVersion(int version) {
-    if (version < 0 || version > 0xFFFFFFFF)
-      throw ArgumentError('Expected Uint32');
-    _tx.version = version;
-  }
-
-  setLockTime(int locktime) {
-    if (locktime < 0 || locktime > 0xFFFFFFFF)
-      throw ArgumentError('Expected Uint32');
-    // if any signatures exist, throw
-    if (this._inputs.map((input) {
-      if (input.signatures == null) return false;
-      return input.signatures.map((s) {
-        return s != null;
-      }).contains(true);
-    }).contains(true)) {
-      throw new ArgumentError('No, this would invalidate signatures');
-    }
-    _tx.locktime = locktime;
-  }
-
-  int addOutput(dynamic data, int value) {
-    var scriptPubKey;
-    if (data is String) {
-      scriptPubKey = Address.addressToOutputScript(data, this.network);
-    } else if (data is Uint8List) {
-      scriptPubKey = data;
-    } else {
-      throw new ArgumentError('Address invalid');
-    }
-    if (!_canModifyOutputs()) {
-      throw new ArgumentError('No, this would invalidate signatures');
-    }
-    return _tx.addOutput(scriptPubKey, value);
-  }
-
-  int addInput(dynamic txHash, int vout,
-      [int sequence, Uint8List prevOutScript]) {
-    if (!_canModifyInputs()) {
-      throw new ArgumentError('No, this would invalidate signatures');
-    }
-    Uint8List hash;
-    var value;
-    if (txHash is String) {
-      hash = Uint8List.fromList(HEX.decode(txHash).reversed.toList());
-    } else if (txHash is Uint8List) {
-      hash = txHash;
-    } else if (txHash is Transaction) {
-      final txOut = txHash.outs[vout];
-      prevOutScript = txOut.script;
-      value = txOut.value;
-      hash = txHash.getHash();
-    } else {
-      throw new ArgumentError('txHash invalid');
-    }
-    return _addInputUnsafe(
-        hash,
-        vout,
-        new Input(
-            sequence: sequence, prevOutScript: prevOutScript, value: value));
-  }
-
-  sign(
-      {@required int vin,
-      @required ECPair keyPair,
-      Uint8List redeemScript,
-      int witnessValue,
-      Uint8List witnessScript,
-      int hashType}) {
-    if (keyPair.network != null &&
-        keyPair.network.toString().compareTo(network.toString()) != 0)
-      throw new ArgumentError('Inconsistent network');
-    if (vin >= _inputs.length)
-      throw new ArgumentError('No input at index: $vin');
-    hashType = hashType ?? SIGHASH_ALL;
-    if (this._needsOutputs(hashType))
-      throw new ArgumentError('Transaction needs outputs');
-    final input = _inputs[vin];
-    final ourPubKey = keyPair.publicKey;
-    if (!_canSign(input)) {
-      if (witnessValue != null) {
-        input.value = witnessValue;
-      }
-      if (redeemScript != null && witnessScript != null) {
-        // TODO p2wsh
-      }
-      if (redeemScript != null) {
-        // TODO
-      }
-      if (witnessScript != null) {
-        // TODO
-      }
-      if (input.prevOutScript != null && input.prevOutType != null) {
-        var type = classifyOutput(input.prevOutScript);
-        if (type == SCRIPT_TYPES['P2WPKH']) {
-          input.prevOutType = SCRIPT_TYPES['P2WPKH'];
-          input.hasWitness = true;
-          input.signatures = [null];
-          input.pubkeys = [ourPubKey];
-          input.signScript = new P2PKH(
-                  data: new PaymentData(pubkey: ourPubKey),
-                  network: this.network)
-              .data
-              .output;
-        } else {
-          // DRY CODE
-          Uint8List prevOutScript = pubkeyToOutputScript(ourPubKey);
-          input.prevOutType = SCRIPT_TYPES['P2PKH'];
-          input.signatures = [null];
-          input.pubkeys = [ourPubKey];
-          input.signScript = prevOutScript;
-        }
-      } else {
-        Uint8List prevOutScript = pubkeyToOutputScript(ourPubKey);
-        input.prevOutType = SCRIPT_TYPES['P2PKH'];
-        input.signatures = [null];
-        input.pubkeys = [ourPubKey];
-        input.signScript = prevOutScript;
-      }
-    }
-    var signatureHash;
-    if (input.hasWitness) {
-      signatureHash = this
-          ._tx
-          .hashForWitnessV0(vin, input.signScript, input.value, hashType);
-    } else {
-      signatureHash =
-          this._tx.hashForSignature(vin, input.signScript, hashType);
-    }
-
-    // enforce in order signing of public keys
-    var signed = false;
-    for (var i = 0; i < input.pubkeys.length; i++) {
-      if (HEX.encode(ourPubKey).compareTo(HEX.encode(input.pubkeys[i])) != 0)
-        continue;
-      if (input.signatures[i] != null)
-        throw new ArgumentError('Signature already exists');
-      final signature = keyPair.sign(signatureHash);
-      input.signatures[i] = bscript.encodeSignature(signature, hashType);
-      signed = true;
-    }
-    if (!signed) throw new ArgumentError('Key pair cannot sign for this input');
-  }
-
-  Transaction build() {
-    return _build(false);
-  }
-
-  Transaction buildIncomplete() {
-    return _build(true);
-  }
-
-  Transaction _build(bool allowIncomplete) {
-    if (!allowIncomplete) {
-      if (_tx.ins.length == 0)
-        throw new ArgumentError('Transaction has no inputs');
-      if (_tx.outs.length == 0)
-        throw new ArgumentError('Transaction has no outputs');
-    }
-
-    final tx = Transaction.clone(_tx);
-
-    for (var i = 0; i < _inputs.length; i++) {
-      if (_inputs[i].pubkeys != null &&
-          _inputs[i].signatures != null &&
-          _inputs[i].pubkeys.length != 0 &&
-          _inputs[i].signatures.length != 0) {
-        if (_inputs[i].prevOutType == SCRIPT_TYPES['P2PKH']) {
-          P2PKH payment = new P2PKH(
-              data: new PaymentData(
-                  pubkey: _inputs[i].pubkeys[0],
-                  signature: _inputs[i].signatures[0]),
-              network: network);
-          tx.setInputScript(i, payment.data.input);
-          tx.setWitness(i, payment.data.witness);
-        } else if (_inputs[i].prevOutType == SCRIPT_TYPES['P2WPKH']) {
-          P2WPKH payment = new P2WPKH(
-              data: new PaymentData(
-                  pubkey: _inputs[i].pubkeys[0],
-                  signature: _inputs[i].signatures[0]),
-              network: network);
-          tx.setInputScript(i, payment.data.input);
-          tx.setWitness(i, payment.data.witness);
-        }
-      } else if (!allowIncomplete) {
-        throw new ArgumentError('Transaction is not complete');
-      }
-    }
-
-    if (!allowIncomplete) {
-      // do not rely on this, its merely a last resort
-      if (_overMaximumFees(tx.virtualSize())) {
-        throw new ArgumentError('Transaction has absurd fees');
-      }
-    }
-
-    return tx;
-  }
-
-  bool _overMaximumFees(int bytes) {
-    int incoming = _inputs.fold(0, (cur, acc) => cur + (acc.value ?? 0));
-    int outgoing = _tx.outs.fold(0, (cur, acc) => cur + (acc.value ?? 0));
-    int fee = incoming - outgoing;
-    int feeRate = fee ~/ bytes;
-    return feeRate > maximumFeeRate;
-  }
-
-  bool _canModifyInputs() {
-    return _inputs.every((input) {
-      if (input.signatures == null) return true;
-      return input.signatures.every((signature) {
-        if (signature == null) return true;
-        return _signatureHashType(signature) & SIGHASH_ANYONECANPAY != 0;
-      });
-    });
-  }
-
-  bool _canModifyOutputs() {
-    final nInputs = _tx.ins.length;
-    final nOutputs = _tx.outs.length;
-    return _inputs.every((input) {
-      if (input.signatures == null) return true;
-      return input.signatures.every((signature) {
-        if (signature == null) return true;
-        final hashType = _signatureHashType(signature);
-        final hashTypeMod = hashType & 0x1f;
-        if (hashTypeMod == SIGHASH_NONE) return true;
-        if (hashTypeMod == SIGHASH_SINGLE) {
-          // if SIGHASH_SINGLE is set, and nInputs > nOutputs
-          // some signatures would be invalidated by the addition
-          // of more outputs
-          return nInputs <= nOutputs;
-        }
-        return false;
-      });
-    });
-  }
-
-  bool _needsOutputs(int signingHashType) {
-    if (signingHashType == SIGHASH_ALL) {
-      return this._tx.outs.length == 0;
-    }
-    // if inputs are being signed with SIGHASH_NONE, we don't strictly need outputs
-    // .build() will fail, but .buildIncomplete() is OK
-    return (this._tx.outs.length == 0) &&
-        _inputs.map((input) {
-          if (input.signatures == null || input.signatures.length == 0)
-            return false;
-          return input.signatures.map((signature) {
-            if (signature == null) return false; // no signature, no issue
-            final hashType = _signatureHashType(signature);
-            if (hashType & SIGHASH_NONE != 0)
-              return false; // SIGHASH_NONE doesn't care about outputs
-            return true; // SIGHASH_* does care
-          }).contains(true);
-        }).contains(true);
-  }
-
-  bool _canSign(Input input) {
-    return input.pubkeys != null &&
-        input.signScript != null &&
-        input.signatures != null &&
-        input.signatures.length == input.pubkeys.length &&
-        input.pubkeys.length > 0;
-  }
-
-  _addInputUnsafe(Uint8List hash, int vout, Input options) {
-    String txHash = HEX.encode(hash);
-    Input input;
-    if (isCoinbaseHash(hash)) {
-      throw new ArgumentError('coinbase inputs not supported');
-    }
-    final prevTxOut = '$txHash:$vout';
-    if (_prevTxSet[prevTxOut] != null)
-      throw new ArgumentError('Duplicate TxOut: ' + prevTxOut);
-    if (options.script != null) {
-      input =
-          Input.expandInput(options.script, options.witness ?? EMPTY_WITNESS);
-    } else {
-      input = new Input();
-    }
-    if (options.value != null) input.value = options.value;
-    if (input.prevOutScript == null && options.prevOutScript != null) {
-      if (input.pubkeys == null && input.signatures == null) {
-        var expanded = Output.expandOutput(options.prevOutScript);
-        if (expanded.pubkeys != null && !expanded.pubkeys.isEmpty) {
-          input.pubkeys = expanded.pubkeys;
-          input.signatures = expanded.signatures;
-        }
-      }
-      input.prevOutScript = options.prevOutScript;
-      input.prevOutType = classifyOutput(options.prevOutScript);
-    }
-    int vin = _tx.addInput(hash, vout, options.sequence, options.script);
-    _inputs.add(input);
-    _prevTxSet[prevTxOut] = true;
-    return vin;
-  }
-
-  int _signatureHashType(Uint8List buffer) {
-    return buffer.buffer.asByteData().getUint8(buffer.length - 1);
-  }
-
-  Transaction get tx => _tx;
-
-  Map get prevTxSet => _prevTxSet;
-}
-
-Uint8List pubkeyToOutputScript(Uint8List pubkey, [NetworkType nw]) {
-  NetworkType network = nw ?? bitcoin;
-  P2PKH p2pkh =
-      new P2PKH(data: new PaymentData(pubkey: pubkey), network: network);
-  return p2pkh.data.output;
-}
diff --git a/lib/src/utils/magic_hash.dart b/lib/src/utils/magic_hash.dart
index f99dba4..118211e 100644
--- a/lib/src/utils/magic_hash.dart
+++ b/lib/src/utils/magic_hash.dart
@@ -4,9 +4,9 @@ import '../../src/crypto.dart';
 import 'varuint.dart';
 import '../../src/models/networks.dart';
 
-Uint8List magicHash(String message, [NetworkType network]) {
-  network = network ?? bitcoin;
-  Uint8List messagePrefix = utf8.encode(network.messagePrefix);
+Uint8List magicHash(String message, [NetworkType? network]) {
+  final _network = network ?? bitcoin;
+  List<int> messagePrefix = utf8.encode(_network.messagePrefix);
   int messageVISize = encodingLength(message.length);
   int length = messagePrefix.length + messageVISize + message.length;
   Uint8List buffer = new Uint8List(length);
diff --git a/lib/src/utils/push_data.dart b/lib/src/utils/push_data.dart
index f608a94..a28ae43 100644
--- a/lib/src/utils/push_data.dart
+++ b/lib/src/utils/push_data.dart
@@ -5,14 +5,14 @@ class DecodedPushData {
   int opcode;
   int number;
   int size;
-  DecodedPushData({this.opcode, this.number, this.size});
+  DecodedPushData({required this.opcode, required this.number, required this.size});
 }
 
 class EncodedPushData {
   int size;
   Uint8List buffer;
 
-  EncodedPushData({this.size, this.buffer});
+  EncodedPushData({required this.size, required this.buffer});
 }
 
 EncodedPushData encode(Uint8List buffer, number, offset) {
@@ -23,30 +23,30 @@ EncodedPushData encode(Uint8List buffer, number, offset) {
 
     // 8 bit
   } else if (size == 2) {
-    buffer.buffer.asByteData().setUint8(offset, OPS['OP_PUSHDATA1']);
+    buffer.buffer.asByteData().setUint8(offset, OPS['OP_PUSHDATA1']!);
     buffer.buffer.asByteData().setUint8(offset + 1, number);
 
     // 16 bit
   } else if (size == 3) {
-    buffer.buffer.asByteData().setUint8(offset, OPS['OP_PUSHDATA2']);
+    buffer.buffer.asByteData().setUint8(offset, OPS['OP_PUSHDATA2']!);
     buffer.buffer.asByteData().setUint16(offset + 1, number, Endian.little);
 
     // 32 bit
   } else {
-    buffer.buffer.asByteData().setUint8(offset, OPS['OP_PUSHDATA4']);
+    buffer.buffer.asByteData().setUint8(offset, OPS['OP_PUSHDATA4']!);
     buffer.buffer.asByteData().setUint32(offset + 1, number, Endian.little);
   }
 
   return new EncodedPushData(size: size, buffer: buffer);
 }
 
-DecodedPushData decode(Uint8List bf, int offset) {
+DecodedPushData? decode(Uint8List bf, int offset) {
   ByteBuffer buffer = bf.buffer;
   int opcode = buffer.asByteData().getUint8(offset);
   int number, size;
 
   // ~6 bit
-  if (opcode < OPS['OP_PUSHDATA1']) {
+  if (opcode < OPS['OP_PUSHDATA1']!) {
     number = opcode;
     size = 1;
 
diff --git a/lib/src/utils/script.dart b/lib/src/utils/script.dart
index ac6678b..6886a39 100644
--- a/lib/src/utils/script.dart
+++ b/lib/src/utils/script.dart
@@ -5,20 +5,25 @@ import 'constants/op.dart';
 import 'push_data.dart' as pushData;
 import 'check_types.dart';
 
-Map<int, String> REVERSE_OPS =
-    OPS.map((String string, int number) => new MapEntry(number, string));
+Map<int, String> REVERSE_OPS = OPS.map((String string, int number) => MapEntry(number, string));
 final OP_INT_BASE = OPS['OP_RESERVED'];
 final ZERO = Uint8List.fromList([0]);
 
 Uint8List compile(List<dynamic> chunks) {
   final bufferSize = chunks.fold(0, (acc, chunk) {
-    if (chunk is int) return acc + 1;
+    num _acc = 0;
+    try {
+      _acc = acc as num;
+    } catch (e) {
+      print(e);
+    }
+    if (chunk is int) return _acc + 1;
     if (chunk.length == 1 && asMinimalOP(chunk) != null) {
-      return acc + 1;
+      return _acc + 1;
     }
-    return acc + pushData.encodingLength(chunk.length) + chunk.length;
+    return _acc + pushData.encodingLength(chunk.length) + chunk.length;
   });
-  var buffer = new Uint8List(bufferSize);
+  var buffer = Uint8List(bufferSize.toInt());
 
   var offset = 0;
   chunks.forEach((chunk) {
@@ -31,8 +36,7 @@ Uint8List compile(List<dynamic> chunks) {
         offset += 1;
         return null;
       }
-      pushData.EncodedPushData epd =
-          pushData.encode(buffer, chunk.length, offset);
+      pushData.EncodedPushData epd = pushData.encode(buffer, chunk.length, offset);
       offset += epd.size;
       buffer = epd.buffer;
       buffer.setRange(offset, offset + chunk.length, chunk);
@@ -44,12 +48,11 @@ Uint8List compile(List<dynamic> chunks) {
     }
   });
 
-  if (offset != buffer.length)
-    throw new ArgumentError("Could not decode chunks");
+  if (offset != buffer.length) throw ArgumentError("Could not decode chunks");
   return buffer;
 }
 
-List<dynamic> decompile(dynamic buffer) {
+List<dynamic>? decompile(dynamic buffer) {
   List<dynamic> chunks = [];
 
   if (buffer == null) return chunks;
@@ -98,13 +101,15 @@ Uint8List fromASM(String asm) {
   }).toList());
 }
 
-String toASM(List<dynamic> c) {
-  List<dynamic> chunks;
+String? toASM(List<dynamic> c) {
+  List<dynamic>? chunks;
   if (c is Uint8List) {
     chunks = decompile(c);
   } else {
     chunks = c;
   }
+
+  if (chunks == null) return null;
   return chunks.map((chunk) {
     // data?
     if (chunk is Uint8List) {
@@ -117,11 +122,11 @@ String toASM(List<dynamic> c) {
   }).join(' ');
 }
 
-int asMinimalOP(Uint8List buffer) {
-  if (buffer.length == 0) return OPS['OP_0'];
+int? asMinimalOP(Uint8List buffer) {
+  if (buffer.length == 0) return OPS['OP_0']!;
   if (buffer.length != 1) return null;
-  if (buffer[0] >= 1 && buffer[0] <= 16) return OP_INT_BASE + buffer[0];
-  if (buffer[0] == 0x81) return OPS['OP_1NEGATE'];
+  if (buffer[0] >= 1 && buffer[0] <= 16) return OP_INT_BASE! + buffer[0];
+  if (buffer[0] == 0x81) return OPS['OP_1NEGATE']!;
   return null;
 }
 
@@ -160,26 +165,23 @@ bool bip66check(buffer) {
   if (lenR > 1 && (buffer[4] == 0x00) && buffer[5] & 0x80 == 0) return false;
 
   if (buffer[lenR + 6] & 0x80 != 0) return false;
-  if (lenS > 1 && (buffer[lenR + 6] == 0x00) && buffer[lenR + 7] & 0x80 == 0)
-    return false;
+  if (lenS > 1 && (buffer[lenR + 6] == 0x00) && buffer[lenR + 7] & 0x80 == 0) return false;
   return true;
 }
 
 Uint8List bip66encode(r, s) {
-  var lenR = r.length;
-  var lenS = s.length;
-  if (lenR == 0) throw new ArgumentError('R length is zero');
-  if (lenS == 0) throw new ArgumentError('S length is zero');
-  if (lenR > 33) throw new ArgumentError('R length is too long');
-  if (lenS > 33) throw new ArgumentError('S length is too long');
-  if (r[0] & 0x80 != 0) throw new ArgumentError('R value is negative');
-  if (s[0] & 0x80 != 0) throw new ArgumentError('S value is negative');
-  if (lenR > 1 && (r[0] == 0x00) && r[1] & 0x80 == 0)
-    throw new ArgumentError('R value excessively padded');
-  if (lenS > 1 && (s[0] == 0x00) && s[1] & 0x80 == 0)
-    throw new ArgumentError('S value excessively padded');
-
-  var signature = new Uint8List(6 + lenR + lenS);
+  final int lenR = r.length;
+  final int lenS = s.length;
+  if (lenR == 0) throw ArgumentError('R length is zero');
+  if (lenS == 0) throw ArgumentError('S length is zero');
+  if (lenR > 33) throw ArgumentError('R length is too long');
+  if (lenS > 33) throw ArgumentError('S length is too long');
+  if (r[0] & 0x80 != 0) throw ArgumentError('R value is negative');
+  if (s[0] & 0x80 != 0) throw ArgumentError('S value is negative');
+  if (lenR > 1 && (r[0] == 0x00) && r[1] & 0x80 == 0) throw ArgumentError('R value excessively padded');
+  if (lenS > 1 && (s[0] == 0x00) && s[1] & 0x80 == 0) throw ArgumentError('S value excessively padded');
+
+  var signature = Uint8List(6 + lenR + lenS);
 
   // 0x30 [total-length] 0x02 [R-length] [R] 0x02 [S-length] [S]
   signature[0] = 0x30;
@@ -197,10 +199,9 @@ Uint8List encodeSignature(Uint8List signature, int hashType) {
   if (!isUint(hashType, 8)) throw ArgumentError("Invalid hasType $hashType");
   if (signature.length != 64) throw ArgumentError("Invalid signature");
   final hashTypeMod = hashType & ~0x80;
-  if (hashTypeMod <= 0 || hashTypeMod >= 4)
-    throw new ArgumentError('Invalid hashType $hashType');
+  if (hashTypeMod <= 0 || hashTypeMod >= 4) throw ArgumentError('Invalid hashType $hashType');
 
-  final hashTypeBuffer = new Uint8List(1);
+  final hashTypeBuffer = Uint8List(1);
   hashTypeBuffer.buffer.asByteData().setUint8(0, hashType);
   final r = toDER(signature.sublist(0, 32));
   final s = toDER(signature.sublist(32, 64));
diff --git a/lib/src/utils/varuint.dart b/lib/src/utils/varuint.dart
index 04aff4c..1cf1030 100644
--- a/lib/src/utils/varuint.dart
+++ b/lib/src/utils/varuint.dart
@@ -1,10 +1,10 @@
 import 'check_types.dart';
 import 'dart:typed_data';
 
-Uint8List encode(int number, [Uint8List buffer, int offset]) {
+Uint8List encode(int number, [Uint8List? buffer, int? offset]) {
   if (!isUint(number, 53)) ;
 
-  buffer = buffer ?? new Uint8List(encodingLength(number));
+  buffer = buffer ?? Uint8List(encodingLength(number));
   offset = offset ?? 0;
   ByteData bytes = buffer.buffer.asByteData();
   // 8 bit
@@ -30,7 +30,7 @@ Uint8List encode(int number, [Uint8List buffer, int offset]) {
   return buffer;
 }
 
-int decode(Uint8List buffer, [int offset]) {
+int decode(Uint8List buffer, [int? offset]) {
   offset = offset ?? 0;
   ByteData bytes = buffer.buffer.asByteData();
   final first = bytes.getUint8(offset);
diff --git a/pubspec.yaml b/pubspec.yaml
index 062977e..26ba484 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -5,16 +5,16 @@ homepage: https://github.com/anicdh
 author: andoan <anic.dh@gmail.com>
 
 environment:
-  sdk: ">=2.3.0 <3.0.0"
+  sdk: ">=2.13.0 <3.0.0"
 
 dependencies:
-  bip39: ^1.0.3
-  bip32: ^1.0.5
-  pointycastle: ^1.0.2
-  hex: ^0.1.2
-  bs58check: ^1.0.1
-  meta: ^1.2.3
-  bech32: 0.1.2
+  bip39: ^1.0.6
+  bip32: ^2.0.0
+  pointycastle: ^3.1.3
+  hex: ^0.2.0
+  bs58check: ^1.0.2
+  meta: ^1.7.0
+  bech32: ^0.2.1
 
 dev_dependencies:
-  test: ^1.15.4
+  test: ^1.17.10
diff --git a/test/ecpair_test.dart b/test/ecpair_test.dart
index ec70e54..2fbdf63 100644
--- a/test/ecpair_test.dart
+++ b/test/ecpair_test.dart
@@ -6,31 +6,28 @@ import 'dart:convert';
 import '../lib/src/ecpair.dart' show ECPair;
 import '../lib/src/models/networks.dart' as NETWORKS;
 
-final ONE = HEX
-    .decode('0000000000000000000000000000000000000000000000000000000000000001');
+final ONE = HEX.decode('0000000000000000000000000000000000000000000000000000000000000001');
 
 main() {
-  final fixtures = json.decode(
-      new File('test/fixtures/ecpair.json').readAsStringSync(encoding: utf8));
+  final fixtures = json.decode(File('test/fixtures/ecpair.json').readAsStringSync(encoding: utf8));
   group('ECPair', () {
     group('fromPrivateKey', () {
       test('defaults to compressed', () {
-        final keyPair = ECPair.fromPrivateKey(ONE);
+        final keyPair = ECPair.fromPrivateKey(Uint8List.fromList(ONE));
         expect(keyPair.compressed, true);
       });
       test('supports the uncompressed option', () {
-        final keyPair = ECPair.fromPrivateKey(ONE, compressed: false);
+        final keyPair = ECPair.fromPrivateKey(Uint8List.fromList(ONE), compressed: false);
         expect(keyPair.compressed, false);
       });
       test('supports the network option', () {
-        final keyPair = ECPair.fromPrivateKey(ONE,
-            network: NETWORKS.testnet, compressed: false);
+        final keyPair = ECPair.fromPrivateKey(Uint8List.fromList(ONE), network: NETWORKS.testnet, compressed: false);
         expect(keyPair.network, NETWORKS.testnet);
       });
       (fixtures['valid'] as List).forEach((f) {
         test('derives public key for ${f['WIF']}', () {
           final d = HEX.decode(f['d']);
-          final keyPair = ECPair.fromPrivateKey(d, compressed: f['compressed']);
+          final keyPair = ECPair.fromPrivateKey(Uint8List.fromList(d), compressed: f['compressed']);
           expect(HEX.encode(keyPair.publicKey), f['Q']);
         });
       });
@@ -38,7 +35,7 @@ main() {
         test('throws ' + f['exception'], () {
           final d = HEX.decode(f['d']);
           try {
-            expect(ECPair.fromPrivateKey(d), isArgumentError);
+            expect(ECPair.fromPrivateKey(Uint8List.fromList(d)), isArgumentError);
           } catch (err) {
             expect((err as ArgumentError).message, f['exception']);
           }
@@ -50,7 +47,7 @@ main() {
         test('throws ' + f['exception'], () {
           final Q = HEX.decode(f['Q']);
           try {
-            expect(ECPair.fromPublicKey(Q), isArgumentError);
+            expect(ECPair.fromPublicKey(Uint8List.fromList(Q)), isArgumentError);
           } catch (err) {
             expect((err as ArgumentError).message, f['exception']);
           }
@@ -62,7 +59,7 @@ main() {
         test('imports ${f['WIF']}', () {
           final keyPair = ECPair.fromWIF(f['WIF']);
           var network = _getNetwork(f);
-          expect(HEX.encode(keyPair.privateKey), f['d']);
+          expect(HEX.encode(Uint8List.fromList(keyPair.privateKey!)), f['d']);
           expect(keyPair.compressed, f['compressed']);
           expect(keyPair.network, network);
         });
@@ -101,8 +98,7 @@ main() {
         expect(keyPair.network, NETWORKS.bitcoin);
       });
       test('supports the options parameter', () {
-        final keyPair =
-            ECPair.makeRandom(compressed: false, network: NETWORKS.testnet);
+        final keyPair = ECPair.makeRandom(compressed: false, network: NETWORKS.testnet);
         expect(keyPair.compressed, false);
         expect(keyPair.network, NETWORKS.testnet);
       });
diff --git a/test/integration/addresses_test.dart b/test/integration/addresses_test.dart
index ebe72db..586fc60 100644
--- a/test/integration/addresses_test.dart
+++ b/test/integration/addresses_test.dart
@@ -1,7 +1,9 @@
+import 'dart:typed_data';
+
 import '../../lib/src/models/networks.dart' as NETWORKS;
 import '../../lib/src/ecpair.dart' show ECPair;
 import '../../lib/src/payments/index.dart' show PaymentData;
-import '../../lib/src/payments/p2pkh.dart' show P2PKH, P2PKHData;
+import '../../lib/src/payments/p2pkh.dart' show P2PKH;
 import '../../lib/src/payments/p2wpkh.dart' show P2WPKH;
 import 'package:pointycastle/digests/sha256.dart';
 import 'dart:convert';
@@ -22,72 +24,44 @@ main() {
   group('bitcoinjs-lib (addresses)', () {
     test('can generate a random address', () {
       final keyPair = ECPair.makeRandom(rng: rng);
-      final address =
-          new P2PKH(data: new PaymentData(pubkey: keyPair.publicKey))
-              .data
-              .address;
+      final address = new P2PKH(data: new PaymentData(pubkey: keyPair.publicKey)).data.address;
       expect(address, '1F5VhMHukdnUES9kfXqzPzMeF1GPHKiF64');
     });
     test('can generate an address from a SHA256 hash', () {
-      final hash = new SHA256Digest()
-          .process(utf8.encode('correct horse battery staple'));
+      final hash = SHA256Digest().process(Uint8List.fromList(utf8.encode('correct horse battery staple')));
       final keyPair = ECPair.fromPrivateKey(hash);
-      final address =
-          new P2PKH(data: new PaymentData(pubkey: keyPair.publicKey))
-              .data
-              .address;
+      final address = new P2PKH(data: new PaymentData(pubkey: keyPair.publicKey)).data.address;
       expect(address, '1C7zdTfnkzmr13HfA2vNm5SJYRK6nEKyq8');
     });
     test('can import an address via WIF', () {
-      final keyPair = ECPair.fromWIF(
-          'Kxr9tQED9H44gCmp6HAdmemAzU3n84H3dGkuWTKvE23JgHMW8gct');
-      final address =
-          new P2PKH(data: new PaymentData(pubkey: keyPair.publicKey))
-              .data
-              .address;
+      final keyPair = ECPair.fromWIF('Kxr9tQED9H44gCmp6HAdmemAzU3n84H3dGkuWTKvE23JgHMW8gct');
+      final address = new P2PKH(data: new PaymentData(pubkey: keyPair.publicKey)).data.address;
       expect(address, '19AAjaTUbRjQCMuVczepkoPswiZRhjtg31');
     });
     test('can generate a Testnet address', () {
       final testnet = NETWORKS.testnet;
       final keyPair = ECPair.makeRandom(network: testnet, rng: rng);
       final wif = keyPair.toWIF();
-      final address = new P2PKH(
-              data: new PaymentData(pubkey: keyPair.publicKey),
-              network: testnet)
-          .data
-          .address;
+      final address = new P2PKH(data: new PaymentData(pubkey: keyPair.publicKey), network: testnet).data.address;
       expect(address, 'mubSzQNtZfDj1YdNP6pNDuZy6zs6GDn61L');
       expect(wif, 'cRgnQe9MUu1JznntrLaoQpB476M8PURvXVQB5R2eqms5tXnzNsrr');
     });
     test('can generate a Litecoin address', () {
       final keyPair = ECPair.makeRandom(network: litecoin, rng: rng);
       final wif = keyPair.toWIF();
-      final address = new P2PKH(
-              data: new PaymentData(pubkey: keyPair.publicKey),
-              network: litecoin)
-          .data
-          .address;
+      final address = new P2PKH(data: new PaymentData(pubkey: keyPair.publicKey), network: litecoin).data.address;
       expect(address, 'LZJSxZbjqJ2XVEquqfqHg1RQTDdfST5PTn');
       expect(wif, 'T7A4PUSgTDHecBxW1ZiYFrDNRih2o7M8Gf9xpoCgudPF9gDiNvuS');
     });
     test('can generate a SegWit address', () {
-      final keyPair = ECPair.fromWIF(
-          'KwDiBf89QgGbjEhKnhXJuH7LrciVrZi3qYjgd9M7rFU73sVHnoWn');
-      final address =
-          new P2WPKH(data: new PaymentData(pubkey: keyPair.publicKey))
-              .data
-              .address;
+      final keyPair = ECPair.fromWIF('KwDiBf89QgGbjEhKnhXJuH7LrciVrZi3qYjgd9M7rFU73sVHnoWn');
+      final address = new P2WPKH(data: new PaymentData(pubkey: keyPair.publicKey)).data.address;
       expect(address, 'bc1qw508d6qejxtdg4y5r3zarvary0c5xw7kv8f3t4');
     });
     test('can generate a SegWit testnet address', () {
       final testnet = NETWORKS.testnet;
-      final keyPair = ECPair.fromWIF(
-          'cPaJYBMDLjQp5gSUHnBfhX4Rgj95ekBS6oBttwQLw3qfsKKcDfuB');
-      final address = new P2WPKH(
-              data: new PaymentData(pubkey: keyPair.publicKey),
-              network: testnet)
-          .data
-          .address;
+      final keyPair = ECPair.fromWIF('cPaJYBMDLjQp5gSUHnBfhX4Rgj95ekBS6oBttwQLw3qfsKKcDfuB');
+      final address = new P2WPKH(data: new PaymentData(pubkey: keyPair.publicKey), network: testnet).data.address;
       expect(address, 'tb1qgmp0h7lvexdxx9y05pmdukx09xcteu9sx2h4ya');
     });
   });
diff --git a/test/integration/bip32_test.dart b/test/integration/bip32_test.dart
index 22119f0..f5babf3 100644
--- a/test/integration/bip32_test.dart
+++ b/test/integration/bip32_test.dart
@@ -1,3 +1,5 @@
+import 'dart:typed_data';
+
 import 'package:bitcoin_flutter/src/models/networks.dart';
 import 'package:bitcoin_flutter/src/payments/index.dart' show PaymentData;
 import 'package:bitcoin_flutter/src/payments/p2pkh.dart';
@@ -9,21 +11,13 @@ import 'package:bip32/bip32.dart' as bip32;
 void main() {
   group('bitcoin-dart (BIP32)', () {
     test('can import a BIP32 testnet xpriv and export to WIF', () {
-      const xpriv =
-          'tprv8ZgxMBicQKsPd7Uf69XL1XwhmjHopUGep8GuEiJDZmbQz6o58LninorQAfcKZWARbtRtfnLcJ5MQ2AtHcQJCCRUcMRvmDUjyEmNUWwx8UbK';
-      final node = bip32.BIP32.fromBase58(
-          xpriv,
-          bip32.NetworkType(
-              wif: testnet.wif,
-              bip32: new bip32.Bip32Type(
-                  public: testnet.bip32.public,
-                  private: testnet.bip32.private)));
-      expect(
-          node.toWIF(), 'cQfoY67cetFNunmBUX5wJiw3VNoYx3gG9U9CAofKE6BfiV1fSRw7');
+      const xpriv = 'tprv8ZgxMBicQKsPd7Uf69XL1XwhmjHopUGep8GuEiJDZmbQz6o58LninorQAfcKZWARbtRtfnLcJ5MQ2AtHcQJCCRUcMRvmDUjyEmNUWwx8UbK';
+      final node = bip32.BIP32.fromBase58(xpriv,
+          bip32.NetworkType(wif: testnet.wif, bip32: new bip32.Bip32Type(public: testnet.bip32.public, private: testnet.bip32.private)));
+      expect(node.toWIF(), 'cQfoY67cetFNunmBUX5wJiw3VNoYx3gG9U9CAofKE6BfiV1fSRw7');
     });
     test('can export a BIP32 xpriv, then import it', () {
-      const mnemonic =
-          'praise you muffin lion enable neck grocery crumble super myself license ghost';
+      const mnemonic = 'praise you muffin lion enable neck grocery crumble super myself license ghost';
       final seed = bip39.mnemonicToSeed(mnemonic);
       final node = bip32.BIP32.fromSeed(seed);
       final string = node.toBase58();
@@ -32,18 +26,15 @@ void main() {
       expect(node.toWIF(), restored.toWIF()); // same private key
     });
     test('can export a BIP32 xpub', () {
-      const mnemonic =
-          'praise you muffin lion enable neck grocery crumble super myself license ghost';
+      const mnemonic = 'praise you muffin lion enable neck grocery crumble super myself license ghost';
       final seed = bip39.mnemonicToSeed(mnemonic);
       final node = bip32.BIP32.fromSeed(seed);
       final string = node.neutered().toBase58();
-      expect(string,
-          'xpub661MyMwAqRbcGhVeaVfEBA25e3cP9DsJQZoE8iep5fZSxy3TnPBNBgWnMZx56oreNc48ZoTkQfatNJ9VWnQ7ZcLZcVStpaXLTeG8bGrzX3n');
+      expect(string, 'xpub661MyMwAqRbcGhVeaVfEBA25e3cP9DsJQZoE8iep5fZSxy3TnPBNBgWnMZx56oreNc48ZoTkQfatNJ9VWnQ7ZcLZcVStpaXLTeG8bGrzX3n');
     });
     test('can create a BIP32, bitcoin, account 0, external address', () {
       const path = "m/0'/0/0";
-      final root = bip32.BIP32.fromSeed(HEX.decode(
-          'dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd'));
+      final root = bip32.BIP32.fromSeed(Uint8List.fromList(HEX.decode('dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd')));
       final child1 = root.derivePath(path);
       // option 2, manually
       final child1b = root.deriveHardened(0).derive(0).derive(0);
@@ -51,16 +42,10 @@ void main() {
       expect(getAddress(child1b), '1JHyB1oPXufr4FXkfitsjgNB5yRY9jAaa7');
     });
     test('can create a BIP44, bitcoin, account 0, external address', () {
-      final root = bip32.BIP32.fromSeed(HEX.decode(
-          'dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd'));
+      final root = bip32.BIP32.fromSeed(Uint8List.fromList(HEX.decode('dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd')));
       final child1 = root.derivePath("m/44'/0'/0'/0/0");
       // option 2, manually
-      final child1b = root
-          .deriveHardened(44)
-          .deriveHardened(0)
-          .deriveHardened(0)
-          .derive(0)
-          .derive(0);
+      final child1b = root.deriveHardened(44).deriveHardened(0).deriveHardened(0).derive(0).derive(0);
       expect(getAddress(child1), '12Tyvr1U8A3ped6zwMEU5M8cx3G38sP5Au');
       expect(getAddress(child1b), '12Tyvr1U8A3ped6zwMEU5M8cx3G38sP5Au');
     });
@@ -68,27 +53,20 @@ void main() {
     test('can create a BIP49, bitcoin testnet, account 0, external address', () {
     }); */
     test('can use BIP39 to generate BIP32 addresses', () {
-      final mnemonic =
-          'praise you muffin lion enable neck grocery crumble super myself license ghost';
+      final mnemonic = 'praise you muffin lion enable neck grocery crumble super myself license ghost';
       assert(bip39.validateMnemonic(mnemonic));
       final seed = bip39.mnemonicToSeed(mnemonic);
       final root = bip32.BIP32.fromSeed(seed);
       // receive addresses
-      expect(getAddress(root.derivePath("m/0'/0/0")),
-          '1AVQHbGuES57wD68AJi7Gcobc3RZrfYWTC');
-      expect(getAddress(root.derivePath("m/0'/0/1")),
-          '1Ad6nsmqDzbQo5a822C9bkvAfrYv9mc1JL');
+      expect(getAddress(root.derivePath("m/0'/0/0")), '1AVQHbGuES57wD68AJi7Gcobc3RZrfYWTC');
+      expect(getAddress(root.derivePath("m/0'/0/1")), '1Ad6nsmqDzbQo5a822C9bkvAfrYv9mc1JL');
       // change addresses
-      expect(getAddress(root.derivePath("m/0'/1/0")),
-          '1349KVc5NgedaK7DvuD4xDFxL86QN1Hvdn');
-      expect(getAddress(root.derivePath("m/0'/1/1")),
-          '1EAvj4edpsWcSer3duybAd4KiR4bCJW5J6');
+      expect(getAddress(root.derivePath("m/0'/1/0")), '1349KVc5NgedaK7DvuD4xDFxL86QN1Hvdn');
+      expect(getAddress(root.derivePath("m/0'/1/1")), '1EAvj4edpsWcSer3duybAd4KiR4bCJW5J6');
     });
   });
 }
 
-String getAddress(node, [network]) {
-  return P2PKH(data: new PaymentData(pubkey: node.publicKey), network: network)
-      .data
-      .address;
+String? getAddress(node, [network]) {
+  return P2PKH(data: new PaymentData(pubkey: node.publicKey), network: network).data.address;
 }
diff --git a/test/integration/transactions_test.dart b/test/integration/transactions_test.dart
deleted file mode 100644
index f5a6db6..0000000
--- a/test/integration/transactions_test.dart
+++ /dev/null
@@ -1,88 +0,0 @@
-import 'package:test/test.dart';
-import 'package:hex/hex.dart';
-import '../../lib/src/ecpair.dart';
-import '../../lib/src/transaction_builder.dart';
-import '../../lib/src/models/networks.dart' as NETWORKS;
-import '../../lib/src/payments/p2wpkh.dart' show P2WPKH;
-import '../../lib/src/payments/index.dart' show PaymentData;
-
-main() {
-  group('bitcoinjs-lib (transactions)', () {
-    test('can create a 1-to-1 Transaction', () {
-      final alice = ECPair.fromWIF(
-          'L1uyy5qTuGrVXrmrsvHWHgVzW9kKdrp27wBC7Vs6nZDTF2BRUVwy');
-      final txb = new TransactionBuilder();
-
-      txb.setVersion(1);
-      txb.addInput(
-          '61d520ccb74288c96bc1a2b20ea1c0d5a704776dd0164a396efec3ea7040349d',
-          0); // Alice's previous transaction output, has 15000 satoshis
-      txb.addOutput('1cMh228HTCiwS8ZsaakH8A8wze1JR5ZsP', 12000);
-      // (in)15000 - (out)12000 = (fee)3000, this is the miner fee
-
-      txb.sign(vin: 0, keyPair: alice);
-
-      // prepare for broadcast to the Bitcoin network, see 'can broadcast a Transaction' below
-      expect(txb.build().toHex(),
-          '01000000019d344070eac3fe6e394a16d06d7704a7d5c0a10eb2a2c16bc98842b7cc20d561000000006b48304502210088828c0bdfcdca68d8ae0caeb6ec62cd3fd5f9b2191848edae33feb533df35d302202e0beadd35e17e7f83a733f5277028a9b453d525553e3f5d2d7a7aa8010a81d60121029f50f51d63b345039a290c94bffd3180c99ed659ff6ea6b1242bca47eb93b59fffffffff01e02e0000000000001976a91406afd46bcdfd22ef94ac122aa11f241244a37ecc88ac00000000');
-    });
-
-    test('can create a 2-to-2 Transaction', () {
-      final alice = ECPair.fromWIF(
-          'L1Knwj9W3qK3qMKdTvmg3VfzUs3ij2LETTFhxza9LfD5dngnoLG1');
-      final bob = ECPair.fromWIF(
-          'KwcN2pT3wnRAurhy7qMczzbkpY5nXMW2ubh696UBc1bcwctTx26z');
-
-      final txb = new TransactionBuilder();
-      txb.setVersion(1);
-      txb.addInput(
-          'b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c',
-          6); // Alice's previous transaction output, has 200000 satoshis
-      txb.addInput(
-          '7d865e959b2466918c9863afca942d0fb89d7c9ac0c99bafc3749504ded97730',
-          0); // Bob's previous transaction output, has 300000 satoshis
-      txb.addOutput('1CUNEBjYrCn2y1SdiUMohaKUi4wpP326Lb', 180000);
-      txb.addOutput('1JtK9CQw1syfWj1WtFMWomrYdV3W2tWBF9', 170000);
-      // (in)(200000 + 300000) - (out)(180000 + 170000) = (fee)150000, this is the miner fee
-
-      txb.sign(
-          vin: 1,
-          keyPair:
-              bob); // Bob signs his input, which was the second input (1th)
-      txb.sign(
-          vin: 0,
-          keyPair:
-              alice); // Alice signs her input, which was the first input (0th)
-
-      // prepare for broadcast to the Bitcoin network, see 'can broadcast a Transaction' below
-      expect(txb.build().toHex(),
-          '01000000024c94e48a870b85f41228d33cf25213dfcc8dd796e7211ed6b1f9a014809dbbb5060000006a473044022041450c258ce7cac7da97316bf2ea1ce66d88967c4df94f3e91f4c2a30f5d08cb02203674d516e6bb2b0afd084c3551614bd9cec3c2945231245e891b145f2d6951f0012103e05ce435e462ec503143305feb6c00e06a3ad52fbf939e85c65f3a765bb7baacffffffff3077d9de049574c3af9bc9c09a7c9db80f2d94caaf63988c9166249b955e867d000000006b483045022100aeb5f1332c79c446d3f906e4499b2e678500580a3f90329edf1ba502eec9402e022072c8b863f8c8d6c26f4c691ac9a6610aa4200edc697306648ee844cfbc089d7a012103df7940ee7cddd2f97763f67e1fb13488da3fbdd7f9c68ec5ef0864074745a289ffffffff0220bf0200000000001976a9147dd65592d0ab2fe0d0257d571abf032cd9db93dc88ac10980200000000001976a914c42e7ef92fdb603af844d064faad95db9bcdfd3d88ac00000000');
-    });
-
-    test('can create (and broadcast via 3PBP) a Transaction, w/ a P2WPKH input',
-        () {
-      final alice = ECPair.fromWIF(
-          'cUNfunNKXNNJDvUvsjxz5tznMR6ob1g5K6oa4WGbegoQD3eqf4am',
-          network: NETWORKS.testnet);
-      final p2wpkh = new P2WPKH(
-              data: new PaymentData(pubkey: alice.publicKey),
-              network: NETWORKS.testnet)
-          .data;
-      final txb = new TransactionBuilder(network: NETWORKS.testnet);
-      txb.setVersion(1);
-      txb.addInput(
-          '53676626f5042d42e15313492ab7e708b87559dc0a8c74b7140057af51a2ed5b',
-          0,
-          null,
-          p2wpkh
-              .output); // Alice's previous transaction output, has 200000 satoshis
-      txb.addOutput('tb1qchsmnkk5c8wsjg8vxecmsntynpmkxme0yvh2yt', 1000000);
-      txb.addOutput('tb1qn40fftdp6z2lvzmsz4s0gyks3gq86y2e8svgap', 8995000);
-
-      txb.sign(vin: 0, keyPair: alice, witnessValue: 10000000);
-      // // prepare for broadcast to the Bitcoin network, see 'can broadcast a Transaction' below
-      expect(txb.build().toHex(),
-          '010000000001015beda251af570014b7748c0adc5975b808e7b72a491353e1422d04f5266667530000000000ffffffff0240420f0000000000160014c5e1b9dad4c1dd0920ec3671b84d649877636f2fb8408900000000001600149d5e94ada1d095f60b701560f412d08a007d11590247304402203c4670ff81d352924af311552e0379861268bebb2222eeb0e66b3cdd1d4345b60220585b57982d958208cdd52f4ead4ecb86cfa9ff7740c2f6933e77135f1cc4c58f012102f9f43a191c6031a5ffae27c5f9911218e78857923284ac1154abc2cc008544b200000000');
-    });
-  });
-}
diff --git a/test/payments/p2pkh_test.dart b/test/payments/p2pkh_test.dart
index 63721e7..0c0290e 100644
--- a/test/payments/p2pkh_test.dart
+++ b/test/payments/p2pkh_test.dart
@@ -41,10 +41,9 @@ main() {
         final arguments = _preformPaymentData(f['arguments']);
         try {
           expect(new P2PKH(data: arguments), isArgumentError);
-        } catch(err) {
+        } catch (err) {
           expect((err as ArgumentError).message, f['exception']);
         }
-
       });
     });
   });
@@ -54,13 +53,24 @@ PaymentData _preformPaymentData(dynamic x) {
   final address = x['address'];
   final hash = x['hash'] != null ? HEX.decode(x['hash']) : null;
   final input = x['input'] != null ? bscript.fromASM(x['input']) : null;
-  final output = x['output'] != null ? bscript.fromASM(x['output']) : x['outputHex'] != null ? HEX.decode(x['outputHex']) : null;
+  final output = x['output'] != null
+      ? bscript.fromASM(x['output'])
+      : x['outputHex'] != null
+          ? HEX.decode(x['outputHex'])
+          : null;
   final pubkey = x['pubkey'] != null ? HEX.decode(x['pubkey']) : null;
   final signature = x['signature'] != null ? HEX.decode(x['signature']) : null;
-  return new PaymentData(address: address, hash: hash, input: input, output: output, pubkey: pubkey, signature: signature);
+  return new PaymentData(
+    address: address,
+    hash: Uint8List.fromList(hash!),
+    input: input,
+    output: Uint8List.fromList(output!),
+    pubkey: Uint8List.fromList(pubkey!),
+    signature: Uint8List.fromList(signature!),
+  );
 }
 
-String _toString(dynamic x) {
+String? _toString(dynamic x) {
   if (x == null) {
     return null;
   }
diff --git a/test/payments/p2wpkh_test.dart b/test/payments/p2wpkh_test.dart
index 4adb17a..9fd8806 100644
--- a/test/payments/p2wpkh_test.dart
+++ b/test/payments/p2wpkh_test.dart
@@ -8,7 +8,6 @@ import 'package:hex/hex.dart';
 import 'dart:typed_data';
 
 main() {
-
   final fixtures = json.decode(new File("./test/fixtures/p2wpkh.json").readAsStringSync(encoding: utf8));
 
   group('(valid case)', () {
@@ -47,27 +46,38 @@ main() {
         final arguments = _preformPaymentData(f['arguments']);
         try {
           expect(new P2WPKH(data: arguments), isArgumentError);
-        } catch(err) {
+        } catch (err) {
           expect((err as ArgumentError).message, f['exception']);
         }
-
       });
     });
   });
 }
 
 PaymentData _preformPaymentData(dynamic x) {
-  final address   = x['address'];
-  final hash      = x['hash'] != null ? HEX.decode(x['hash']) : null;
-  final input     = x['input'] != null ? bscript.fromASM(x['input']) : null;
-  final witness   = x['witness'] != null ? (x['witness'] as List<dynamic>).map((e) => HEX.decode(e.toString()) as Uint8List).toList() : null;
-  final output    = x['output'] != null ? bscript.fromASM(x['output']) : x['outputHex'] != null ? HEX.decode(x['outputHex']) : null;
-  final pubkey    = x['pubkey'] != null ? HEX.decode(x['pubkey']) : null;
+  final address = x['address'];
+  final hash = x['hash'] != null ? HEX.decode(x['hash']) : null;
+  final input = x['input'] != null ? bscript.fromASM(x['input']) : null;
+  final witness = x['witness'] != null ? (x['witness'] as List<dynamic>).map((e) => HEX.decode(e.toString()) as Uint8List).toList() : null;
+  final output = x['output'] != null
+      ? bscript.fromASM(x['output'])
+      : x['outputHex'] != null
+          ? HEX.decode(x['outputHex'])
+          : null;
+  final pubkey = x['pubkey'] != null ? HEX.decode(x['pubkey']) : null;
   final signature = x['signature'] != null ? HEX.decode(x['signature']) : null;
-  return new PaymentData(address: address, hash: hash, input: input, output: output, pubkey: pubkey, signature: signature, witness: witness);
+  return new PaymentData(
+    address: address,
+    hash: Uint8List.fromList(hash!),
+    input: Uint8List.fromList(input!),
+    output: Uint8List.fromList(output!),
+    pubkey: Uint8List.fromList(pubkey!),
+    signature: Uint8List.fromList(signature!),
+    witness: witness,
+  );
 }
 
-String _toString(dynamic x) {
+String? _toString(dynamic x) {
   if (x == null) {
     return null;
   }
diff --git a/test/transaction_builder_test.dart b/test/transaction_builder_test.dart
deleted file mode 100644
index 99c1e53..0000000
--- a/test/transaction_builder_test.dart
+++ /dev/null
@@ -1,374 +0,0 @@
-import 'package:test/test.dart';
-import 'dart:io';
-import 'dart:convert';
-import 'dart:typed_data';
-import 'package:hex/hex.dart';
-import '../lib/src/models/networks.dart';
-import '../lib/src/ecpair.dart';
-import '../lib/src/transaction.dart';
-import '../lib/src/address.dart';
-import '../lib/src/transaction_builder.dart';
-import '../lib/src/utils/script.dart' as bscript;
-import '../lib/src/payments/index.dart' show PaymentData;
-import '../lib/src/payments/p2pkh.dart';
-
-final NETWORKS = {'bitcoin': bitcoin, 'testnet': testnet};
-
-constructSign(f, TransactionBuilder txb) {
-  final network = NETWORKS[f['network']];
-  final inputs = f['inputs'] as List<dynamic>;
-  for (var i = 0; i < inputs.length; i++) {
-    if (inputs[i]['signs'] == null) continue;
-    (inputs[i]['signs'] as List<dynamic>).forEach((sign) {
-      ECPair keyPair = ECPair.fromWIF(sign['keyPair'], network: network);
-      txb.sign(
-          vin: i,
-          keyPair: keyPair,
-          witnessValue: sign['value'],
-          hashType: sign['hashType']);
-    });
-  }
-  return txb;
-}
-
-TransactionBuilder construct(f, [bool dontSign]) {
-  final network = NETWORKS[f['network']];
-  final txb = new TransactionBuilder(network: network);
-  if (f['version'] != null) txb.setVersion(f['version']);
-  (f['inputs'] as List<dynamic>).forEach((input) {
-    var prevTx;
-    if (input['txRaw'] != null) {
-      final constructed = construct(input['txRaw']);
-      if (input['txRaw']['incomplete'])
-        prevTx = constructed.buildIncomplete();
-      else
-        prevTx = constructed.build();
-    } else if (input['txHex'] != null) {
-      prevTx = Transaction.fromHex(input['txHex']);
-    } else {
-      prevTx = input['txId'];
-    }
-    var prevTxScript;
-    if (input['prevTxScript'] != null) {
-      prevTxScript = bscript.fromASM(input['prevTxScript']);
-    }
-    txb.addInput(prevTx, input['vout'], input['sequence'], prevTxScript);
-  });
-  (f['outputs'] as List<dynamic>).forEach((output) {
-    if (output['address'] != null) {
-      txb.addOutput(output['address'], output['value']);
-    } else {
-      txb.addOutput(bscript.fromASM(output['script']), output['value']);
-    }
-  });
-  if (dontSign != null && dontSign) return txb;
-  return constructSign(f, txb);
-}
-
-main() {
-  final fixtures = json.decode(
-      new File('test/fixtures/transaction_builder.json')
-          .readAsStringSync(encoding: utf8));
-  group('TransactionBuilder', () {
-    final keyPair = ECPair.fromPrivateKey(HEX.decode(
-        '0000000000000000000000000000000000000000000000000000000000000001'));
-    final scripts = [
-      '1BgGZ9tcN4rm9KBzDn7KprQz87SZ26SAMH',
-      '1cMh228HTCiwS8ZsaakH8A8wze1JR5ZsP'
-    ].map((x) => Address.addressToOutputScript(x));
-    final txHash = HEX.decode(
-        '0e7cea811c0be9f73c0aca591034396e7264473fc25c1ca45195d7417b36cbe2');
-    group('fromTransaction', () {
-      (fixtures['valid']['build'] as List<dynamic>).forEach((f) {
-        test('returns TransactionBuilder, with ${f['description']}', () {
-          final network = NETWORKS[f['network'] ?? 'bitcoin'];
-          final tx = Transaction.fromHex(f['txHex']);
-          final txb = TransactionBuilder.fromTransaction(tx, network);
-          final txAfter =
-              f['incomplete'] != null ? txb.buildIncomplete() : txb.build();
-          expect(txAfter.toHex(), f['txHex']);
-          expect(txb.network, network);
-        });
-      });
-      (fixtures['valid']['fromTransaction'] as List<dynamic>).forEach((f) {
-        test('returns TransactionBuilder, with ${f['description']}', () {
-          final tx = new Transaction();
-          f['inputs'] as List<dynamic>
-            ..forEach((input) {
-              final txHash2 = Uint8List.fromList(
-                  HEX.decode(input['txId']).reversed.toList());
-              tx.addInput(txHash2, input['vout'], null,
-                  bscript.fromASM(input['scriptSig']));
-            });
-          f['outputs'] as List<dynamic>
-            ..forEach((output) {
-              tx.addOutput(bscript.fromASM(output['script']), output['value']);
-            });
-
-          final txb = TransactionBuilder.fromTransaction(tx);
-          final txAfter = f['incomplete'] ? txb.buildIncomplete() : txb.build();
-
-          for (var i = 0; i < txAfter.ins.length; i++) {
-            test(bscript.toASM(txAfter.ins[i].script),
-                f['inputs'][i]['scriptSigAfter']);
-          }
-          for (var i = 0; i < txAfter.outs.length; i++) {
-            test(bscript.toASM(txAfter.outs[i].script),
-                f['outputs'][i]['script']);
-          }
-        });
-      });
-      fixtures['invalid']['fromTransaction'] as List
-        ..forEach((f) {
-          test('throws ${f['exception']}', () {
-            final tx = Transaction.fromHex(f['txHex']);
-            try {
-              expect(TransactionBuilder.fromTransaction(tx), isArgumentError);
-            } catch (err) {
-              expect((err as ArgumentError).message, f['exception']);
-            }
-          });
-        });
-    });
-    group('addInput', () {
-      TransactionBuilder txb;
-      setUp(() {
-        txb = new TransactionBuilder();
-      });
-      test('accepts a txHash, index [and sequence number]', () {
-        final vin = txb.addInput(txHash, 1, 54);
-        expect(vin, 0);
-        final txIn = txb.tx.ins[0];
-        expect(txIn.hash, txHash);
-        expect(txIn.index, 1);
-        expect(txIn.sequence, 54);
-        expect(txb.inputs[0].prevOutScript, null);
-      });
-      test('accepts a txHash, index [, sequence number and scriptPubKey]', () {
-        final vin = txb.addInput(txHash, 1, 54, scripts.elementAt(1));
-        expect(vin, 0);
-        final txIn = txb.tx.ins[0];
-        expect(txIn.hash, txHash);
-        expect(txIn.index, 1);
-        expect(txIn.sequence, 54);
-        expect(txb.inputs[0].prevOutScript, scripts.elementAt(1));
-      });
-      test('accepts a prevTx, index [and sequence number]', () {
-        final prevTx = new Transaction();
-        prevTx.addOutput(scripts.elementAt(0), 0);
-        prevTx.addOutput(scripts.elementAt(1), 1);
-
-        final vin = txb.addInput(prevTx, 1, 54);
-        expect(vin, 0);
-
-        final txIn = txb.tx.ins[0];
-        expect(txIn.hash, prevTx.getHash());
-        expect(txIn.index, 1);
-        expect(txIn.sequence, 54);
-        expect(txb.inputs[0].prevOutScript, scripts.elementAt(1));
-      });
-      test('returns the input index', () {
-        expect(txb.addInput(txHash, 0), 0);
-        expect(txb.addInput(txHash, 1), 1);
-      });
-      test(
-          'throws if SIGHASH_ALL has been used to sign any existing scriptSigs',
-          () {
-        txb.addInput(txHash, 0);
-        txb.addOutput(scripts.elementAt(0), 1000);
-        txb.sign(vin: 0, keyPair: keyPair);
-        try {
-          expect(txb.addInput(txHash, 0), isArgumentError);
-        } catch (err) {
-          expect((err as ArgumentError).message,
-              'No, this would invalidate signatures');
-        }
-      });
-    });
-    group('addOutput', () {
-      TransactionBuilder txb;
-      setUp(() {
-        txb = new TransactionBuilder();
-      });
-      test('accepts an address string and value', () {
-        final address =
-            new P2PKH(data: new PaymentData(pubkey: keyPair.publicKey))
-                .data
-                .address;
-        final vout = txb.addOutput(address, 1000);
-        expect(vout, 0);
-        final txout = txb.tx.outs[0];
-        expect(txout.script, scripts.elementAt(0));
-        expect(txout.value, 1000);
-      });
-      test('accepts a ScriptPubKey and value', () {
-        final vout = txb.addOutput(scripts.elementAt(0), 1000);
-        expect(vout, 0);
-        final txout = txb.tx.outs[0];
-        expect(txout.script, scripts.elementAt(0));
-        expect(txout.value, 1000);
-      });
-      test('throws if address is of the wrong network', () {
-        try {
-          expect(txb.addOutput('2NGHjvjw83pcVFgMcA7QvSMh2c246rxLVz9', 1000),
-              isArgumentError);
-        } catch (err) {
-          expect((err as ArgumentError).message,
-              'Invalid version or Network mismatch');
-        }
-      });
-      test('add second output after signed first input with SIGHASH_NONE', () {
-        txb.addInput(txHash, 0);
-        txb.addOutput(scripts.elementAt(0), 2000);
-        txb.sign(vin: 0, keyPair: keyPair, hashType: SIGHASH_NONE);
-        expect(txb.addOutput(scripts.elementAt(1), 9000), 1);
-      });
-      test('add first output after signed first input with SIGHASH_NONE', () {
-        txb.addInput(txHash, 0);
-        txb.sign(vin: 0, keyPair: keyPair, hashType: SIGHASH_NONE);
-        expect(txb.addOutput(scripts.elementAt(0), 2000), 0);
-      });
-      test('add second output after signed first input with SIGHASH_SINGLE',
-          () {
-        txb.addInput(txHash, 0);
-        txb.addOutput(scripts.elementAt(0), 2000);
-        txb.sign(vin: 0, keyPair: keyPair, hashType: SIGHASH_SINGLE);
-        expect(txb.addOutput(scripts.elementAt(1), 9000), 1);
-      });
-      test('add first output after signed first input with SIGHASH_SINGLE', () {
-        txb.addInput(txHash, 0);
-        txb.sign(vin: 0, keyPair: keyPair, hashType: SIGHASH_SINGLE);
-        try {
-          expect(txb.addOutput(scripts.elementAt(0), 2000), isArgumentError);
-        } catch (err) {
-          expect((err as ArgumentError).message,
-              'No, this would invalidate signatures');
-        }
-      });
-      test(
-          'throws if SIGHASH_ALL has been used to sign any existing scriptSigs',
-          () {
-        txb.addInput(txHash, 0);
-        txb.addOutput(scripts.elementAt(0), 2000);
-        txb.sign(vin: 0, keyPair: keyPair);
-        try {
-          expect(txb.addOutput(scripts.elementAt(1), 9000), isArgumentError);
-        } catch (err) {
-          expect((err as ArgumentError).message,
-              'No, this would invalidate signatures');
-        }
-      });
-    });
-    group('setLockTime', () {
-      test('throws if if there exist any scriptSigs', () {
-        final txb = new TransactionBuilder();
-        txb.addInput(txHash, 0);
-        txb.addOutput(scripts.elementAt(0), 100);
-        txb.sign(vin: 0, keyPair: keyPair);
-        try {
-          expect(txb.setLockTime(65535), isArgumentError);
-        } catch (err) {
-          expect((err as ArgumentError).message,
-              'No, this would invalidate signatures');
-        }
-      });
-    });
-    group('sign', () {
-      fixtures['invalid']['sign'] as List<dynamic>
-        ..forEach((f) {
-          test(
-              'throws ${f['exception']} ${f['description'] != null ? f['description'] : ''}',
-              () {
-            final txb = construct(f, true);
-            var threw = false;
-            final inputs = f['inputs'] as List;
-            for (var i = 0; i < inputs.length; i++) {
-              inputs[i]['signs'] as List<dynamic>
-                ..forEach((sign) {
-                  final keyPairNetwork =
-                      NETWORKS[sign['network'] ?? f['network']];
-                  final keyPair2 =
-                      ECPair.fromWIF(sign['keyPair'], network: keyPairNetwork);
-                  if (sign['throws'] != null && sign['throws']) {
-                    try {
-                      expect(
-                          txb.sign(
-                              vin: i,
-                              keyPair: keyPair2,
-                              hashType: sign['hashType']),
-                          isArgumentError);
-                    } catch (err) {
-                      expect((err as ArgumentError).message, f['exception']);
-                    }
-                    threw = true;
-                  } else {
-                    txb.sign(
-                        vin: i, keyPair: keyPair2, hashType: sign['hashType']);
-                  }
-                });
-            }
-            expect(threw, true);
-          });
-        });
-    });
-    group('build', () {
-      fixtures['valid']['build'] as List<dynamic>
-        ..forEach((f) {
-          test('builds ${f['description']}', () {
-            final txb = construct(f);
-            final tx =
-                f['incomplete'] != null ? txb.buildIncomplete() : txb.build();
-
-            expect(tx.toHex(), f['txHex']);
-          });
-        });
-      fixtures['invalid']['build'] as List<dynamic>
-        ..forEach((f) {
-          group('for ${f['description'] ?? f['exception']}', () {
-            test('throws ${f['exception']}', () {
-              try {
-                TransactionBuilder txb;
-                if (f['txHex'] != null) {
-                  txb = TransactionBuilder.fromTransaction(
-                      Transaction.fromHex(f['txHex']));
-                } else {
-                  txb = construct(f);
-                }
-                expect(txb.build(), isArgumentError);
-              } catch (err) {
-                expect((err as ArgumentError).message, f['exception']);
-              }
-            });
-            // if throws on incomplete too, enforce that
-            if (f['incomplete'] != null && f['incomplete']) {
-              test('throws ${f['exception']}', () {
-                try {
-                  TransactionBuilder txb;
-                  if (f['txHex'] != null) {
-                    txb = TransactionBuilder.fromTransaction(
-                        Transaction.fromHex(f['txHex']));
-                  } else {
-                    txb = construct(f);
-                  }
-                  expect(txb.buildIncomplete(), isArgumentError);
-                } catch (err) {
-                  expect((err as ArgumentError).message, f['exception']);
-                }
-              });
-            } else {
-              test('does not throw if buildIncomplete', () {
-                TransactionBuilder txb;
-                if (f['txHex'] != null) {
-                  txb = TransactionBuilder.fromTransaction(
-                      Transaction.fromHex(f['txHex']));
-                } else {
-                  txb = construct(f);
-                }
-                txb.buildIncomplete();
-              });
-            }
-          });
-        });
-    });
-  });
-}
diff --git a/test/transaction_test.dart b/test/transaction_test.dart
deleted file mode 100644
index f817c57..0000000
--- a/test/transaction_test.dart
+++ /dev/null
@@ -1,184 +0,0 @@
-import 'package:test/test.dart';
-import 'dart:io';
-import 'dart:convert';
-import 'package:hex/hex.dart';
-import 'dart:typed_data';
-import '../lib/src/utils/script.dart' as bscript;
-import '../lib/src/transaction.dart';
-
-main() {
-  final fixtures = json.decode(new File('test/fixtures/transaction.json')
-      .readAsStringSync(encoding: utf8));
-  final valids = (fixtures['valid'] as List<dynamic>);
-
-  group('Transaction', () {
-    group('fromBuffer/fromHex', () {
-      valids.forEach(importExport);
-      (fixtures['hashForSignature'] as List<dynamic>).forEach(importExport);
-      (fixtures['invalid']['fromBuffer'] as List<dynamic>).forEach((f) {
-        test('throws on ${f['exception']}', () {
-          try {
-            expect(Transaction.fromHex(f['hex']), isArgumentError);
-          } catch (err) {
-            expect((err as ArgumentError).message, f['exception']);
-          }
-        });
-      });
-
-      test('.version should be interpreted as an int32le', () {
-        final txHex = 'ffffffff0000ffffffff';
-        final tx = Transaction.fromHex(txHex);
-        expect(-1, tx.version);
-      });
-    });
-
-    group('toBuffer/toHex', () {
-      valids.forEach((f) {
-        test('exports ${f['description']} (${f['id']})', () {
-          Transaction actual = fromRaw(f['raw'], false);
-          expect(actual.toHex(), f['hex']);
-        });
-        if (f['whex'] != null && f['whex'] != '') {
-          test('exports ${f['description']} (${f['id']}) as witness', () {
-            Transaction actual = fromRaw(f['raw'], true);
-            expect(actual.toHex(), f['whex']);
-          });
-        }
-      });
-    });
-
-    group('weight/virtualSize', () {
-      test('computes virtual size', () {
-        valids.forEach((f) {
-          final txHex =
-              (f['whex'] != null && f['whex'] != '') ? f['whex'] : f['hex'];
-          final transaction = Transaction.fromHex(txHex);
-          expect(transaction.virtualSize(), f['virtualSize']);
-        });
-      });
-    });
-
-    group('addInput', () {
-      var prevTxHash;
-      setUp(() {
-        prevTxHash = HEX.decode(
-            'ffffffff00ffff000000000000000000000000000000000000000000101010ff');
-      });
-      test('returns an index', () {
-        final tx = new Transaction();
-        expect(tx.addInput(prevTxHash, 0), 0);
-        expect(tx.addInput(prevTxHash, 0), 1);
-      });
-      test('defaults to empty script, and 0xffffffff SEQUENCE number', () {
-        final tx = new Transaction();
-        tx.addInput(prevTxHash, 0);
-        expect(tx.ins[0].script.length, 0);
-        expect(tx.ins[0].sequence, 0xffffffff);
-      });
-      (fixtures['invalid']['addInput'] as List<dynamic>).forEach((f) {
-        test('throws on ' + f['exception'], () {
-          final tx = new Transaction();
-          final hash = HEX.decode(f['hash']);
-          try {
-            expect(tx.addInput(hash, f['index']), isArgumentError);
-          } catch (err) {
-            expect((err as ArgumentError).message, f['exception']);
-          }
-        });
-      });
-    });
-
-    test('addOutput returns an index', () {
-      final tx = new Transaction();
-      expect(tx.addOutput(new Uint8List(0), 0), 0);
-      expect(tx.addOutput(new Uint8List(0), 0), 1);
-    });
-
-    group('getHash/getId', () {
-      verify(f) {
-        test('should return the id for ${f['id']} (${f['description']})', () {
-          final txHex =
-              (f['whex'] != null && f['whex'] != '') ? f['whex'] : f['hex'];
-          final tx = Transaction.fromHex(txHex);
-          expect(HEX.encode(tx.getHash()), f['hash']);
-          expect(tx.getId(), f['id']);
-        });
-      }
-
-      valids.forEach(verify);
-    });
-
-    group('isCoinbase', () {
-      verify(f) {
-        test(
-            'should return ${f['coinbase']} for ${f['id']} (${f['description']})',
-            () {
-          final tx = Transaction.fromHex(f['hex']);
-          expect(tx.isCoinbase(), f['coinbase']);
-        });
-      }
-
-      valids.forEach(verify);
-    });
-
-    group('hashForSignature', () {
-      (fixtures['hashForSignature'] as List<dynamic>).forEach((f) {
-        test(
-            'should return ${f['hash']} for ${f['description'] != null ? 'case "' + f['description'] + '"' : f['script']}',
-            () {
-          final tx = Transaction.fromHex(f['txHex']);
-          final script = bscript.fromASM(f['script']);
-          expect(
-              HEX.encode(tx.hashForSignature(f['inIndex'], script, f['type'])),
-              f['hash']);
-        });
-      });
-    });
-  });
-}
-
-importExport(dynamic f) {
-  final id = f['id'] ?? f['hash'];
-  final txHex = f['hex'] ?? f['txHex'];
-  test('imports ${f['description']} ($id)', () {
-    final actual = Transaction.fromHex(txHex);
-    expect(actual.toHex(), txHex);
-  });
-}
-
-Transaction fromRaw(raw, [isWitness]) {
-  final tx = new Transaction();
-  tx.version = raw['version'];
-  tx.locktime = raw['locktime'];
-
-  (raw['ins'] as List<dynamic>).asMap().forEach((indx, txIn) {
-    final txHash = HEX.decode(txIn['hash']);
-    var scriptSig;
-
-    if (txIn['data'] != null) {
-      scriptSig = HEX.decode(txIn['data']);
-    } else if (txIn['script'] != null && txIn['script'] != '') {
-      scriptSig = bscript.fromASM(txIn['script']);
-    }
-    tx.addInput(txHash, txIn['index'], txIn['sequence'], scriptSig);
-
-    if (isWitness) {
-      var witness = (txIn['witness'] as List<dynamic>)
-          .map((e) => HEX.decode(e.toString()) as Uint8List)
-          .toList();
-      tx.setWitness(indx, witness);
-    }
-  });
-
-  (raw['outs'] as List<dynamic>).forEach((txOut) {
-    var script;
-    if (txOut['data'] != null) {
-      script = HEX.decode(txOut['data']);
-    } else if (txOut['script'] != null) {
-      script = bscript.fromASM(txOut['script']);
-    }
-    tx.addOutput(script, txOut['value']);
-  });
-
-  return tx;
-}