CBMC: Prove indcpa_enc

This plugs together the various CBMC contracts to prove the full
indcpa_enc.

To make this work we have to slightly change the contract of
poly_getnoise_eta1122_4x to allow argument 1+2 and
argument 3+4 to come from the same polyvec.
That function is only used in indcpa_enc.

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

cbmc/proofs/indcpa_enc/Makefile

@@ -0,0 +1,79 @@
+# SPDX-License-Identifier: Apache-2.0
+
+include ../Makefile_params.common
+
+HARNESS_ENTRY = harness
+HARNESS_FILE = indcpa_enc_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 = indcpa_enc
+
+DEFINES +=
+INCLUDES +=
+
+REMOVE_FUNCTION_BODY +=
+UNWINDSET +=
+
+PROOF_SOURCES += $(PROOFDIR)/$(HARNESS_FILE).c
+PROJECT_SOURCES += $(SRCDIR)/mlkem/indcpa.c
+
+CHECK_FUNCTION_CONTRACTS=$(MLKEM_NAMESPACE)indcpa_enc
+
+USED_FUNCTIONS = poly_frommsg
+USED_FUNCTIONS += gen_matrix
+ifeq ($(MLKEM_K),2)
+USED_FUNCTIONS += poly_getnoise_eta1122_4x
+USED_FUNCTIONS += poly_getnoise_eta2
+else ifeq ($(MLKEM_K),3)
+USED_FUNCTIONS += poly_getnoise_eta1_4x
+else ifeq ($(MLKEM_K),4)
+USED_FUNCTIONS += poly_getnoise_eta1_4x
+USED_FUNCTIONS += poly_getnoise_eta2
+endif
+
+USED_FUNCTIONS += polyvec_ntt
+USED_FUNCTIONS += polyvec_mulcache_compute
+USED_FUNCTIONS += polyvec_basemul_acc_montgomery_cached
+USED_FUNCTIONS += polyvec_invntt_tomont
+USED_FUNCTIONS += poly_invntt_tomont
+USED_FUNCTIONS += polyvec_add
+USED_FUNCTIONS += poly_add
+USED_FUNCTIONS += polyvec_reduce
+USED_FUNCTIONS += poly_reduce
+USED_FUNCTIONS += polyvec_compress
+USED_FUNCTIONS += poly_compress
+
+USE_FUNCTION_CONTRACTS=unpack_pk matvec_mul $(addprefix $(MLKEM_NAMESPACE),$(USED_FUNCTIONS))
+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 = $(MLKEM_NAMESPACE)indcpa_enc
+
+# 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 = 10
+
+# 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
+# ("mlkem/poly.c") in PROJECT_SOURCES).
+# REWRITTEN_SOURCES = $(PROOFDIR)/<__SOURCE_FILE_BASENAME__>.i
+# include ../Makefile.common
+# $(PROOFDIR)/<__SOURCE_FILE_BASENAME__>.i_SOURCE = $(SRCDIR)/mlkem/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

cbmc/proofs/indcpa_enc/cbmc-proof.txt

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: Apache-2.0
+
+# This file marks this directory as containing a CBMC proof.

cbmc/proofs/indcpa_enc/indcpa_enc_harness.c

@@ -0,0 +1,28 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: MIT-0
+
+/*
+ * Insert copyright notice
+ */
+
+/**
+ * @file indcpa_keypair_derand_harness.c
+ * @brief Implements the proof harness for indcpa_keypair_derand function.
+ */
+
+/*
+ * Insert project header files that
+ *   - include the declaration of the function
+ *   - include the types needed to declare function arguments
+ */
+#include <indcpa.h>
+#include <poly.h>
+
+/**
+ * @brief Starting point for formal analysis
+ *
+ */
+void harness(void) {
+  uint8_t *a, *b, *c, *d;
+  indcpa_enc(a, b, c, d);
+}

mlkem/indcpa.h

@@ -36,7 +36,13 @@ void indcpa_keypair_derand(
 void indcpa_enc(uint8_t c[MLKEM_INDCPA_BYTES],
                 const uint8_t m[MLKEM_INDCPA_MSGBYTES],
                 const uint8_t pk[MLKEM_INDCPA_PUBLICKEYBYTES],
-                const uint8_t coins[MLKEM_SYMBYTES]);
+                const uint8_t coins[MLKEM_SYMBYTES])  // clang-format off
+  REQUIRES(IS_FRESH(c, MLKEM_INDCPA_BYTES))
+  REQUIRES(IS_FRESH(m, MLKEM_INDCPA_MSGBYTES))
+  REQUIRES(IS_FRESH(pk, MLKEM_INDCPA_PUBLICKEYBYTES))
+  REQUIRES(IS_FRESH(coins, MLKEM_SYMBYTES))
+  ASSIGNS(OBJECT_WHOLE(c));
+// clang-format on
 
 #define indcpa_dec MLKEM_NAMESPACE(indcpa_dec)
 void indcpa_dec(uint8_t m[MLKEM_INDCPA_MSGBYTES],

mlkem/poly.h

@@ -517,10 +517,9 @@ void poly_getnoise_eta1122_4x(poly *r0, poly *r1, poly *r2, poly *r3,
                               const uint8_t seed[MLKEM_SYMBYTES],
                               uint8_t nonce0, uint8_t nonce1, uint8_t nonce2,
                               uint8_t nonce3)  // clang-format off
-REQUIRES(IS_FRESH(r0, sizeof(poly)))
-REQUIRES(IS_FRESH(r1, sizeof(poly)))
-REQUIRES(IS_FRESH(r2, sizeof(poly)))
-REQUIRES(IS_FRESH(r3, sizeof(poly)))
+REQUIRES( /* r0, r1 consecutive, r2, r3 consecutive */
+ (IS_FRESH(r0, 2 * sizeof(poly)) && IS_FRESH(r2, 2 * sizeof(poly)) &&
+   r1 == r0 + 1 && r3 == r2 + 1 && !SAME_OBJECT(r0, r2)))
 REQUIRES(IS_FRESH(seed, MLKEM_SYMBYTES))
 ASSIGNS(OBJECT_WHOLE(r0), OBJECT_WHOLE(r1), OBJECT_WHOLE(r2), OBJECT_WHOLE(r3))
 ENSURES(                                                                          \