CBMC: Add proof and spec for poly_uniform_eta_4x

Resolves #249

Signed-off-by: Matthias J. Kannwischer <[email protected]>

Author: mkannwischer

mldsa/poly.c

@@ -545,6 +545,18 @@ void poly_uniform_eta_4x(poly *r0, poly *r1, poly *r2, poly *r3,
   buflen = STREAM256_BLOCKBYTES;
   while (ctr[0] < MLDSA_N || ctr[1] < MLDSA_N || ctr[2] < MLDSA_N ||
          ctr[3] < MLDSA_N)
+  __loop__(
+    assigns(ctr, state, memory_slice(r0, sizeof(poly)),
+            memory_slice(r1, sizeof(poly)), memory_slice(r2, sizeof(poly)), 
+            memory_slice(r3, sizeof(poly)), object_whole(buf[0]),
+            object_whole(buf[1]), object_whole(buf[2]), 
+            object_whole(buf[3]))
+    invariant(ctr[0] <= MLDSA_N && ctr[1] <= MLDSA_N)
+    invariant(ctr[2] <= MLDSA_N && ctr[3] <= MLDSA_N)
+    invariant(array_abs_bound(r0->coeffs, 0, ctr[0], MLDSA_ETA + 1))
+    invariant(array_abs_bound(r1->coeffs, 0, ctr[1], MLDSA_ETA + 1))
+    invariant(array_abs_bound(r2->coeffs, 0, ctr[2], MLDSA_ETA + 1))
+    invariant(array_abs_bound(r3->coeffs, 0, ctr[3], MLDSA_ETA + 1)))
   {
     mld_xof256_x4_squeezeblocks(buf, 1, &state);
     ctr[0] = rej_eta(r0->coeffs, MLDSA_N, ctr[0], buf[0], buflen);

mldsa/poly.h

@@ -351,7 +351,22 @@ __contract__(
  **************************************************/
 void poly_uniform_eta_4x(poly *r0, poly *r1, poly *r2, poly *r3,
                          const uint8_t seed[MLDSA_CRHBYTES], uint8_t nonce0,
-                         uint8_t nonce1, uint8_t nonce2, uint8_t nonce3);
+                         uint8_t nonce1, uint8_t nonce2, uint8_t nonce3)
+__contract__(
+  requires(memory_no_alias(r0, sizeof(poly)))
+  requires(memory_no_alias(r1, sizeof(poly)))
+  requires(memory_no_alias(r2, sizeof(poly)))
+  requires(memory_no_alias(r3, sizeof(poly)))
+  requires(memory_no_alias(seed, MLDSA_CRHBYTES))
+  assigns(memory_slice(r0, sizeof(poly)))
+  assigns(memory_slice(r1, sizeof(poly)))
+  assigns(memory_slice(r2, sizeof(poly)))
+  assigns(memory_slice(r3, sizeof(poly)))
+  ensures(array_abs_bound(r0->coeffs, 0, MLDSA_N, MLDSA_ETA + 1))
+  ensures(array_abs_bound(r1->coeffs, 0, MLDSA_N, MLDSA_ETA + 1))
+  ensures(array_abs_bound(r2->coeffs, 0, MLDSA_N, MLDSA_ETA + 1))
+  ensures(array_abs_bound(r3->coeffs, 0, MLDSA_N, MLDSA_ETA + 1))
+);
 
 #define poly_uniform_gamma1 MLD_NAMESPACE(poly_uniform_gamma1)
 /*************************************************

proofs/cbmc/poly_uniform_eta_4x/Makefile

@@ -0,0 +1,55 @@
+# Copyright (c) The mldsa-native project authors
+# SPDX-License-Identifier: Apache-2.0 OR ISC OR MIT
+
+include ../Makefile_params.common
+
+HARNESS_ENTRY = harness
+HARNESS_FILE = poly_uniform_eta_4x_harness
+
+# This should be a unique identifier for this proof, and will appear on the
+# Litani dashboard. It can be human-readable and contain spaces if you wish.
+PROOF_UID = poly_uniform_eta_4x
+
+DEFINES +=
+INCLUDES +=
+
+REMOVE_FUNCTION_BODY +=
+UNWINDSET +=
+
+PROOF_SOURCES += $(PROOFDIR)/$(HARNESS_FILE).c
+PROJECT_SOURCES += $(SRCDIR)/mldsa/poly.c $(SRCDIR)/mldsa/fips202/fips202x4.c
+
+CHECK_FUNCTION_CONTRACTS=$(MLD_NAMESPACE)poly_uniform_eta_4x
+USE_FUNCTION_CONTRACTS=$(FIPS202_NAMESPACE)shake256x4_absorb_once $(FIPS202_NAMESPACE)shake256x4_squeezeblocks rej_eta
+APPLY_LOOP_CONTRACTS=on
+USE_DYNAMIC_FRAMES=1
+
+# Disable any setting of EXTERNAL_SAT_SOLVER, and choose SMT backend instead
+EXTERNAL_SAT_SOLVER=
+CBMCFLAGS=--smt2
+
+FUNCTION_NAME = poly_uniform_eta_4x
+
+# If this proof is found to consume huge amounts of RAM, you can set the
+# EXPENSIVE variable. With new enough versions of the proof tools, this will
+# restrict the number of EXPENSIVE CBMC jobs running at once. See the
+# documentation in Makefile.common under the "Job Pools" heading for details.
+# EXPENSIVE = true
+
+# This function is large enough to need...
+CBMC_OBJECT_BITS = 9
+
+# If you require access to a file-local ("static") function or object to conduct
+# your proof, set the following (and do not include the original source file
+# ("mldsa/poly.c") in PROJECT_SOURCES).
+# REWRITTEN_SOURCES = $(PROOFDIR)/<__SOURCE_FILE_BASENAME__>.i
+# include ../Makefile.common
+# $(PROOFDIR)/<__SOURCE_FILE_BASENAME__>.i_SOURCE = $(SRCDIR)/mldsa/poly.c
+# $(PROOFDIR)/<__SOURCE_FILE_BASENAME__>.i_FUNCTIONS = foo bar
+# $(PROOFDIR)/<__SOURCE_FILE_BASENAME__>.i_OBJECTS = baz
+# Care is required with variables on the left-hand side: REWRITTEN_SOURCES must
+# be set before including Makefile.common, but any use of variables on the
+# left-hand side requires those variables to be defined. Hence, _SOURCE,
+# _FUNCTIONS, _OBJECTS is set after including Makefile.common.
+
+include ../Makefile.common

proofs/cbmc/poly_uniform_eta_4x/poly_uniform_eta_4x_harness.c

@@ -0,0 +1,13 @@
+// Copyright (c) The mldsa-native project authors
+// SPDX-License-Identifier: Apache-2.0 OR ISC OR MIT
+
+#include "poly.h"
+
+void harness(void)
+{
+  poly *r0, *r1, *r2, *r3;
+  const uint8_t *seed;
+  uint8_t n0, n1, n2, n3;
+
+  poly_uniform_eta_4x(r0, r1, r2, r3, seed, n0, n1, n2, n3);
+}