CBMC: Add proof and contract for mldsa_shake256_stream_init

Signed-off-by: Jake Massimo <[email protected]>

Author: jakemas

mldsa/symmetric-shake.c

@@ -27,7 +27,7 @@ void mldsa_shake256_stream_init(keccak_state *state,
                                 uint16_t nonce)
 {
   uint8_t t[2];
-  t[0] = nonce;
+  t[0] = nonce & 0xFF;
   t[1] = nonce >> 8;
 
   shake256_init(state);

mldsa/symmetric.h

@@ -27,7 +27,12 @@ __contract__(
 #define mldsa_shake256_stream_init MLD_NAMESPACE(mldsa_shake256_stream_init)
 void mldsa_shake256_stream_init(keccak_state *state,
                                 const uint8_t seed[MLDSA_CRHBYTES],
-                                uint16_t nonce);
+                                uint16_t nonce)
+__contract__(
+  requires(memory_no_alias(state, sizeof(keccak_state)))
+  requires(memory_no_alias(seed, MLDSA_CRHBYTES))
+  assigns(memory_slice(state, sizeof(keccak_state)))
+);
 
 #define STREAM128_BLOCKBYTES SHAKE128_RATE
 #define STREAM256_BLOCKBYTES SHAKE256_RATE

proofs/cbmc/mldsa_shake256_stream_init/Makefile

@@ -0,0 +1,55 @@
+# SPDX-License-Identifier: Apache-2.0
+
+include ../Makefile_params.common
+
+HARNESS_ENTRY = harness
+HARNESS_FILE = mldsa_shake256_stream_init_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 = mldsa_shake256_stream_init
+
+DEFINES +=
+INCLUDES +=
+
+REMOVE_FUNCTION_BODY +=
+UNWINDSET +=
+
+PROOF_SOURCES += $(PROOFDIR)/$(HARNESS_FILE).c
+PROJECT_SOURCES += $(SRCDIR)/mldsa/symmetric-shake.c
+
+CHECK_FUNCTION_CONTRACTS=$(MLD_NAMESPACE)mldsa_shake256_stream_init
+USE_FUNCTION_CONTRACTS=$(FIPS202_NAMESPACE)shake256_init $(FIPS202_NAMESPACE)shake256_absorb $(FIPS202_NAMESPACE)shake256_finalize
+
+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 = mldsa_shake256_stream_init
+
+# 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/mldsa_shake256_stream_init/mldsa_shake256_stream_init_harness.c

@@ -0,0 +1,14 @@
+// Copyright (c) 2025 The mldsa-native project authors
+// SPDX-License-Identifier: Apache-2.0
+
+#include "params.h"
+#include "symmetric.h"
+
+void harness(void)
+{
+  keccak_state *s;
+  const uint8_t *seed;
+  uint16_t nonce;
+
+  mldsa_shake256_stream_init(s, seed, nonce);
+}