Serial FIPS202 3/3: Adapt mld_polyvec_matrix_expand

This commit changes mld_polyvec_matrix_expand to use only poly_uniform
in case MLD_CONFIG_SERIAL_FIPS202_ONLY is set.

A CBMC proof is added.
This change closely follows
pq-code-package/mlkem-native@c670e1d

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

Author: mkannwischer

mldsa/poly.c

@@ -352,6 +352,7 @@ void mld_poly_uniform(mld_poly *a, const uint8_t seed[MLDSA_SEEDBYTES + 2])
   mld_zeroize(buf, sizeof(buf));
 }
 
+#if !defined(MLD_CONFIG_SERIAL_FIPS202_ONLY)
 MLD_INTERNAL_API
 void mld_poly_uniform_4x(mld_poly *vec0, mld_poly *vec1, mld_poly *vec2,
                          mld_poly *vec3,
@@ -416,6 +417,7 @@ void mld_poly_uniform_4x(mld_poly *vec0, mld_poly *vec1, mld_poly *vec2,
   mld_zeroize(buf, sizeof(buf));
 }
 
+#endif /* !MLD_CONFIG_SERIAL_FIPS202_ONLY */
 
 MLD_INTERNAL_API
 void mld_polyt1_pack(uint8_t *r, const mld_poly *a)

mldsa/polyvec.c

@@ -54,6 +54,8 @@ void mld_polyvec_matrix_expand(mld_polyvecl mat[MLDSA_K],
   {
     mld_memcpy(seed_ext[j], rho, MLDSA_SEEDBYTES);
   }
+
+#if !defined(MLD_CONFIG_SERIAL_FIPS202_ONLY)
   /* Sample 4 matrix entries a time. */
   for (i = 0; i < (MLDSA_K * MLDSA_L / 4) * 4; i += 4)
   __loop__(
@@ -86,6 +88,9 @@ void mld_polyvec_matrix_expand(mld_polyvecl mat[MLDSA_K],
                         &mat[(i + 3) / MLDSA_L].vec[(i + 3) % MLDSA_L],
                         seed_ext);
   }
+#else  /* !MLD_CONFIG_SERIAL_FIPS202_ONLY */
+  i = 0;
+#endif /* MLD_CONFIG_SERIAL_FIPS202_ONLY */
 
   /* For MLDSA_K=6, MLDSA_L=5, process the last two entries individually */
   while (i < MLDSA_K * MLDSA_L)

proofs/cbmc/polyvec_matrix_expand_serial/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 = polyvec_matrix_expand_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 = polyvec_matrix_expand_serial
+
+DEFINES += -DMLD_CONFIG_SERIAL_FIPS202_ONLY
+INCLUDES +=
+
+REMOVE_FUNCTION_BODY +=
+UNWINDSET +=
+
+PROOF_SOURCES += $(PROOFDIR)/$(HARNESS_FILE).c
+PROJECT_SOURCES += $(SRCDIR)/mldsa/polyvec.c
+
+CHECK_FUNCTION_CONTRACTS=$(MLD_NAMESPACE)polyvec_matrix_expand
+USE_FUNCTION_CONTRACTS=$(MLD_NAMESPACE)poly_uniform
+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 --arrays-uf-always --slice-formula
+
+FUNCTION_NAME = polyvec_matrix_expand_serial
+
+# 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 = 11
+
+# 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/polyvec_matrix_expand_serial/polyvec_matrix_expand_harness.c

@@ -0,0 +1,12 @@
+// Copyright (c) The mldsa-native project authors
+// SPDX-License-Identifier: Apache-2.0 OR ISC OR MIT
+
+#include "polyvec.h"
+
+void harness(void)
+{
+  mld_polyvecl *mat;
+  uint8_t *rho;
+
+  mld_polyvec_matrix_expand(mat, rho);
+}