CBMC: Add contract and proof for polyveck_pack_w1

Resolves #136

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

Author: mkannwischer

mldsa/poly.h

@@ -523,13 +523,13 @@ __contract__(
   requires(memory_no_alias(r, MLDSA_POLYW1_PACKEDBYTES))
   requires(memory_no_alias(a, sizeof(poly)))
   requires(array_bound(a->coeffs, 0, MLDSA_N, 0, 16))
-  assigns(object_whole(r)));
+  assigns(memory_slice(r, MLDSA_POLYW1_PACKEDBYTES)));
 #elif MLDSA_GAMMA2 == (MLDSA_Q - 1) / 88
 __contract__(
   requires(memory_no_alias(r, MLDSA_POLYW1_PACKEDBYTES))
   requires(memory_no_alias(a, sizeof(poly)))
   requires(array_bound(a->coeffs, 0, MLDSA_N, 0, 44))
-  assigns(object_whole(r)));
+  assigns(memory_slice(r, MLDSA_POLYW1_PACKEDBYTES)));
 #else
 #error "Invalid value of MLDSA_GAMMA2"
 #endif

mldsa/polyvec.h

@@ -372,8 +372,35 @@ __contract__(
 void polyveck_use_hint(polyveck *w, const polyveck *v, const polyveck *h);
 
 #define polyveck_pack_w1 MLD_NAMESPACE(polyveck_pack_w1)
+/*************************************************
+ * Name:        polyveck_pack_w1
+ *
+ * Description: Bit-pack polynomial vector w1 with coefficients in [0,15] or 
+ *              [0,43].
+ *              Input coefficients are assumed to be standard representatives.
+ *
+ * Arguments:   - uint8_t *r: pointer to output byte array with at least
+ *                            MLDSA_K* MLDSA_POLYW1_PACKEDBYTES bytes
+ *              - const polyveck *a: pointer to input polynomial vector
+ **************************************************/
 void polyveck_pack_w1(uint8_t r[MLDSA_K * MLDSA_POLYW1_PACKEDBYTES],
-                      const polyveck *w1);
+                      const polyveck *w1)
+#if MLDSA_MODE == 2
+__contract__(
+  requires(memory_no_alias(r, MLDSA_K * MLDSA_POLYW1_PACKEDBYTES))
+  requires(memory_no_alias(w1, sizeof(polyveck)))
+  requires(forall(k1, 0, MLDSA_K,
+    array_bound(w1->vec[k1].coeffs, 0, MLDSA_N, 0, 44)))
+  assigns(object_whole(r)));
+#else
+__contract__(
+  requires(memory_no_alias(r, MLDSA_K * MLDSA_POLYW1_PACKEDBYTES))
+  requires(memory_no_alias(w1, sizeof(polyveck)))
+  requires(forall(k1, 0, MLDSA_K,
+    array_bound(w1->vec[k1].coeffs, 0, MLDSA_N, 0, 16)))
+  assigns(object_whole(r)));
+#endif
+
 
 #define polyveck_pack_eta MLD_NAMESPACE(polyveck_pack_eta)
 void polyveck_pack_eta(uint8_t r[MLDSA_K * MLDSA_POLYETA_PACKEDBYTES],

proofs/cbmc/polyveck_pack_w1/Makefile

@@ -0,0 +1,54 @@
+# SPDX-License-Identifier: Apache-2.0
+
+include ../Makefile_params.common
+
+HARNESS_ENTRY = harness
+HARNESS_FILE = polyveck_pack_w1_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 = polyveck_pack_w1
+
+DEFINES +=
+INCLUDES +=
+
+REMOVE_FUNCTION_BODY +=
+UNWINDSET += $(MLD_NAMESPACE)polyveck_pack_w1.0:8 # Largest value of MLDSA_K
+
+PROOF_SOURCES += $(PROOFDIR)/$(HARNESS_FILE).c
+PROJECT_SOURCES += $(SRCDIR)/mldsa/polyvec.c
+
+CHECK_FUNCTION_CONTRACTS=$(MLD_NAMESPACE)polyveck_pack_w1
+USE_FUNCTION_CONTRACTS=$(MLD_NAMESPACE)polyw1_pack
+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 = polyveck_pack_w1
+
+# 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 = 8
+
+# 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/polyveck_pack_w1/polyveck_pack_w1_harness.c

@@ -0,0 +1,11 @@
+// Copyright (c) 2025 The mldsa-native project authors
+// SPDX-License-Identifier: Apache-2.0
+
+#include "polyvec.h"
+
+void harness(void)
+{
+  polyveck *a;
+  uint8_t *b;
+  polyveck_pack_w1(b, a);
+}