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crypto_sign_secp256k1: fix hashing heuristics #252

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crypto_sign_secp256k1: fix hashing heuristics #252

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10fb72b
crypto_sign_secp256k1: fix hashing heuristics
RomarQ Aug 27, 2025
c9e000d
Address remark from review
RomarQ Aug 27, 2025
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21 changes: 18 additions & 3 deletions app/src/crypto.c
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Original file line number Diff line number Diff line change
Expand Up @@ -154,8 +154,24 @@ zxerr_t crypto_sign_secp256k1(
}

// Hash the message
uint8_t messageDigest[CX_KECCAK_256_SIZE] = {0};
CHECK_CX_OK(cx_keccak_256_hash(message, messageLen, messageDigest));
uint8_t messageDigest[BLAKE2B_DIGEST_SIZE] = {0};
zxerr_t error = zxerr_unknown;

// When the payload is bigger than MAX_SIGN_SIZE, it needs to be hashed with blake2b_256 before hashing with keccak_256.
// https://github.com/paritytech/polkadot-sdk/blob/1a512570552119a49a8ecb2abfb7021954c4422d/substrate/primitives/runtime/src/generic/unchecked_extrinsic.rs#L567
if (messageLen > MAX_SIGN_SIZE) {
uint8_t intermediate_digest[BLAKE2B_DIGEST_SIZE];
// Hash it with blake2b
cx_blake2b_t ctx;
CATCH_CXERROR(cx_blake2b_init_no_throw(&ctx, 256));
CATCH_CXERROR(cx_hash_no_throw(&ctx.header, CX_LAST, message, messageLen, intermediate_digest, BLAKE2B_DIGEST_SIZE));

// Then hash with keccak_256
CHECK_CX_OK(cx_keccak_256_hash(intermediate_digest, BLAKE2B_DIGEST_SIZE, messageDigest));
} else {
// Mandatory, hash the message with keccak_256
CHECK_CX_OK(cx_keccak_256_hash(message, messageLen, messageDigest));
}

cx_ecfp_private_key_t cx_privateKey;
uint8_t privateKeyData[SECP256K1_PK_LEN_UNCOMPRESSED - 1] = {0};
Expand All @@ -164,7 +180,6 @@ zxerr_t crypto_sign_secp256k1(
*sigSize = 0;

signature_t *const signature = (signature_t *)output;
zxerr_t error = zxerr_unknown;

CATCH_CXERROR(os_derive_bip32_with_seed_no_throw(HDW_NORMAL, CX_CURVE_SECP256K1, hdPath, HDPATH_LEN_DEFAULT,
privateKeyData, NULL, NULL, 0));
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