Merge pull request #384 from pq-code-package/cbmc_indcpa_dec

CBMC Proof of indcpa_dec()

cbmc/proofs/indcpa_dec/Makefile

@@ -0,0 +1,61 @@
+# SPDX-License-Identifier: Apache-2.0
+
+include ../Makefile_params.common
+
+HARNESS_ENTRY = harness
+HARNESS_FILE = indcpa_dec_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_dec
+
+DEFINES +=
+INCLUDES +=
+
+REMOVE_FUNCTION_BODY +=
+UNWINDSET +=
+
+PROOF_SOURCES += $(PROOFDIR)/$(HARNESS_FILE).c
+PROJECT_SOURCES += $(SRCDIR)/mlkem/indcpa.c
+
+CHECK_FUNCTION_CONTRACTS=$(MLKEM_NAMESPACE)indcpa_dec
+
+USED_FUNCTIONS = polyvec_ntt
+USED_FUNCTIONS += polyvec_basemul_acc_montgomery
+USED_FUNCTIONS += poly_invntt_tomont
+USED_FUNCTIONS += poly_sub
+USED_FUNCTIONS += poly_reduce
+USED_FUNCTIONS += poly_tomsg
+USE_FUNCTION_CONTRACTS=unpack_ciphertext unpack_sk $(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_dec
+
+# 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_dec/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_dec/indcpa_dec_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_dec_harness.c
+ * @brief Implements the proof harness for indcpa_dec 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 *m, *c, *sk;
+  indcpa_dec(m, c, sk);
+}

cbmc/proofs/unpack_ciphertext/Makefile

@@ -0,0 +1,54 @@
+# SPDX-License-Identifier: Apache-2.0
+
+include ../Makefile_params.common
+
+HARNESS_ENTRY = harness
+HARNESS_FILE = unpack_ciphertext_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 = unpack_ciphertext
+
+DEFINES +=
+INCLUDES +=
+
+REMOVE_FUNCTION_BODY +=
+UNWINDSET +=
+
+PROOF_SOURCES += $(PROOFDIR)/$(HARNESS_FILE).c
+PROJECT_SOURCES += $(SRCDIR)/mlkem/indcpa.c
+
+CHECK_FUNCTION_CONTRACTS=unpack_ciphertext
+USE_FUNCTION_CONTRACTS=$(MLKEM_NAMESPACE)polyvec_decompress $(MLKEM_NAMESPACE)poly_decompress
+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 = unpack_ciphertext
+
+# 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
+# ("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/unpack_ciphertext/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/unpack_ciphertext/unpack_ciphertext_harness.c

@@ -0,0 +1,20 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: MIT-0 AND Apache-2.0
+
+#include <stdint.h>
+#include "polyvec.h"
+
+void unpack_ciphertext(polyvec *b, poly *v,
+                       const uint8_t c[MLKEM_INDCPA_BYTES]);
+
+/**
+ * @brief Starting point for formal analysis
+ *
+ */
+void harness(void) {
+  polyvec *b;
+  poly *v;
+  uint8_t *c;
+
+  unpack_ciphertext(b, v, c);
+}

mlkem/indcpa.c

@@ -153,8 +153,19 @@ static void pack_ciphertext(uint8_t r[MLKEM_INDCPA_BYTES], polyvec *b,
  *              - poly *v: pointer to the output polynomial v
  *              - const uint8_t *c: pointer to the input serialized ciphertext
  **************************************************/
-static void unpack_ciphertext(polyvec *b, poly *v,
-                              const uint8_t c[MLKEM_INDCPA_BYTES]) {
+STATIC_TESTABLE
+void unpack_ciphertext(polyvec *b, poly *v,
+                       const uint8_t c[MLKEM_INDCPA_BYTES])  // clang-format off
+REQUIRES(IS_FRESH(b, sizeof(polyvec)))
+REQUIRES(IS_FRESH(v, sizeof(poly)))
+REQUIRES(IS_FRESH(c, MLKEM_INDCPA_BYTES))
+ASSIGNS(OBJECT_WHOLE(b))
+ASSIGNS(OBJECT_WHOLE(v))
+ENSURES(FORALL(int, k0, 0, MLKEM_K - 1,
+         ARRAY_IN_BOUNDS(0, (MLKEM_N - 1), b->vec[k0].coeffs, 0, (MLKEM_Q - 1))))
+ENSURES(ARRAY_IN_BOUNDS(0, (MLKEM_N - 1), v->coeffs, 0, (MLKEM_Q - 1)))
+// clang-format on
+{
   polyvec_decompress(b, c);
   poly_decompress(v, c + MLKEM_POLYVECCOMPRESSEDBYTES);
 }
@@ -525,20 +536,6 @@ void indcpa_enc(uint8_t c[MLKEM_INDCPA_BYTES],
   pack_ciphertext(c, &b, &v);
 }
 
-/*************************************************
- * Name:        indcpa_dec
- *
- * Description: Decryption function of the CPA-secure
- *              public-key encryption scheme underlying Kyber.
- *
- * Arguments:   - uint8_t *m: pointer to output decrypted message
- *                            (of length MLKEM_INDCPA_MSGBYTES)
- *              - const uint8_t *c: pointer to input ciphertext
- *                                  (of length MLKEM_INDCPA_BYTES)
- *              - const uint8_t *sk: pointer to input secret key
- *                                   (of length MLKEM_INDCPA_SECRETKEYBYTES)
- **************************************************/
-
 // Check that the arithmetic in indcpa_dec() does not overflow
 STATIC_ASSERT(INVNTT_BOUND + MLKEM_Q < INT16_MAX, indcpa_dec_bound_0)
 

mlkem/indcpa.h

@@ -33,6 +33,19 @@ void indcpa_keypair_derand(
 // clang-format on
 
 #define indcpa_enc MLKEM_NAMESPACE(indcpa_enc)
+/*************************************************
+ * Name:        indcpa_dec
+ *
+ * Description: Decryption function of the CPA-secure
+ *              public-key encryption scheme underlying Kyber.
+ *
+ * Arguments:   - uint8_t *m: pointer to output decrypted message
+ *                            (of length MLKEM_INDCPA_MSGBYTES)
+ *              - const uint8_t *c: pointer to input ciphertext
+ *                                  (of length MLKEM_INDCPA_BYTES)
+ *              - const uint8_t *sk: pointer to input secret key
+ *                                   (of length MLKEM_INDCPA_SECRETKEYBYTES)
+ **************************************************/
 void indcpa_enc(uint8_t c[MLKEM_INDCPA_BYTES],
                 const uint8_t m[MLKEM_INDCPA_MSGBYTES],
                 const uint8_t pk[MLKEM_INDCPA_PUBLICKEYBYTES],
@@ -45,8 +58,13 @@ void indcpa_enc(uint8_t c[MLKEM_INDCPA_BYTES],
 // clang-format on
 
 #define indcpa_dec MLKEM_NAMESPACE(indcpa_dec)
-void indcpa_dec(uint8_t m[MLKEM_INDCPA_MSGBYTES],
-                const uint8_t c[MLKEM_INDCPA_BYTES],
-                const uint8_t sk[MLKEM_INDCPA_SECRETKEYBYTES]);
+void indcpa_dec(
+    uint8_t m[MLKEM_INDCPA_MSGBYTES], const uint8_t c[MLKEM_INDCPA_BYTES],
+    const uint8_t sk[MLKEM_INDCPA_SECRETKEYBYTES])  // clang-format off
+  REQUIRES(IS_FRESH(c, MLKEM_INDCPA_BYTES))
+  REQUIRES(IS_FRESH(m, MLKEM_INDCPA_MSGBYTES))
+  REQUIRES(IS_FRESH(sk, MLKEM_INDCPA_SECRETKEYBYTES))
+  ASSIGNS(OBJECT_WHOLE(m));
+// clang-format on
 
 #endif