CBMC: Add proof and spec for polyvecl_uniform_gamma1

Resolves #115
Adapted from #250.

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

Author: mkannwischer

mldsa/polyvec.h

@@ -17,8 +17,28 @@ typedef struct
 } polyvecl;
 
 #define polyvecl_uniform_gamma1 MLD_NAMESPACE(polyvecl_uniform_gamma1)
+/*************************************************
+ * Name:        polyvecl_uniform_gamma1
+ *
+ * Description: Sample vector of polynomials with uniformly random coefficients
+ *              in [-(MLDSA_GAMMA1 - 1), MLDSA_GAMMA1] by unpacking output
+ *              stream of SHAKE256(seed|nonce)
+ *
+ * Arguments:   - polyvecl *v: pointer to output vector
+ *              - const uint8_t seed[]: byte array with seed of length
+ *                MLDSA_CRHBYTES
+ *              - uint16_t nonce: 16-bit nonce
+ *************************************************/
 void polyvecl_uniform_gamma1(polyvecl *v, const uint8_t seed[MLDSA_CRHBYTES],
-                             uint16_t nonce);
+                             uint16_t nonce)
+__contract__(
+  requires(memory_no_alias(v, sizeof(polyvecl)))
+  requires(memory_no_alias(seed, MLDSA_CRHBYTES))
+  requires(nonce <= (UINT16_MAX - MLDSA_L) / MLDSA_L)
+  assigns(memory_slice(v, sizeof(polyvecl)))
+  ensures(forall(k0, 0, MLDSA_L,
+    array_bound(v->vec[k0].coeffs, 0, MLDSA_N, -(MLDSA_GAMMA1 - 1), MLDSA_GAMMA1 + 1)))
+);
 
 #define polyvecl_reduce MLD_NAMESPACE(polyvecl_reduce)
 /*************************************************

proofs/cbmc/polyvecl_uniform_gamma1/Makefile

@@ -0,0 +1,59 @@
+# 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 = polyvecl_uniform_gamma1_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 = polyvecl_uniform_gamma1
+
+DEFINES +=
+INCLUDES +=
+
+REMOVE_FUNCTION_BODY +=
+UNWINDSET +=
+
+PROOF_SOURCES += $(PROOFDIR)/$(HARNESS_FILE).c
+PROJECT_SOURCES += $(SRCDIR)/mldsa/polyvec.c
+
+CHECK_FUNCTION_CONTRACTS=$(MLD_NAMESPACE)polyvecl_uniform_gamma1
+USE_FUNCTION_CONTRACTS=$(MLD_NAMESPACE)poly_uniform_gamma1_4x
+ifeq ($(MLDSA_MODE),3)
+USE_FUNCTION_CONTRACTS+=$(MLD_NAMESPACE)poly_uniform_gamma1
+endif
+
+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 = polyvecl_uniform_gamma1
+
+# 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/polyvecl_uniform_gamma1/polyvecl_uniform_gamma1_harness.c

@@ -0,0 +1,13 @@
+// Copyright (c) The mldsa-native project authors
+// SPDX-License-Identifier: Apache-2.0 OR ISC OR MIT
+
+#include "polyvec.h"
+
+void harness(void)
+{
+  polyvecl *v;
+  const uint8_t *seed;
+  uint16_t nonce;
+
+  polyvecl_uniform_gamma1(v, seed, nonce);
+}