From 7b4816194e550a5cb07e9557e7ec19923c1219e8 Mon Sep 17 00:00:00 2001
From: Hanno Becker <beckphan@amazon.co.uk>
Date: Sat, 9 Nov 2024 06:10:29 +0000
Subject: [PATCH] CBMC: Prove type+memory-safety of crypto_kem_keypair_derand

This commit brings together the numerous low-level proofs to
a proof of type-safety and memory-safety of the top-level
MLKEM key generation API `crypto_kem_keypair_derand()`.

Signed-off-by: Hanno Becker <beckphan@amazon.co.uk>
---
 .../proofs/crypto_kem_keypair_derand/Makefile | 54 +++++++++++++++++++
 .../crypto_kem_keypair_derand/cbmc-proof.txt  |  3 ++
 .../crypto_kem_keypair_derand_harness.c       | 27 ++++++++++
 mlkem/kem.h                                   | 10 +++-
 4 files changed, 93 insertions(+), 1 deletion(-)
 create mode 100644 cbmc/proofs/crypto_kem_keypair_derand/Makefile
 create mode 100644 cbmc/proofs/crypto_kem_keypair_derand/cbmc-proof.txt
 create mode 100644 cbmc/proofs/crypto_kem_keypair_derand/crypto_kem_keypair_derand_harness.c

diff --git a/cbmc/proofs/crypto_kem_keypair_derand/Makefile b/cbmc/proofs/crypto_kem_keypair_derand/Makefile
new file mode 100644
index 000000000..c89fc716f
--- /dev/null
+++ b/cbmc/proofs/crypto_kem_keypair_derand/Makefile
@@ -0,0 +1,54 @@
+# SPDX-License-Identifier: Apache-2.0
+
+include ../Makefile_params.common
+
+HARNESS_ENTRY = harness
+HARNESS_FILE = crypto_kem_keypair_derand_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 = crypto_kem_keypair_derand
+
+DEFINES +=
+INCLUDES +=
+
+REMOVE_FUNCTION_BODY +=
+UNWINDSET +=
+
+PROOF_SOURCES += $(PROOFDIR)/$(HARNESS_FILE).c
+PROJECT_SOURCES += $(SRCDIR)/mlkem/kem.c
+
+CHECK_FUNCTION_CONTRACTS=$(MLKEM_NAMESPACE)keypair_derand
+USE_FUNCTION_CONTRACTS=$(FIPS202_NAMESPACE)sha3_256 $(MLKEM_NAMESPACE)indcpa_keypair_derand
+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)keypair_derand
+
+# 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
diff --git a/cbmc/proofs/crypto_kem_keypair_derand/cbmc-proof.txt b/cbmc/proofs/crypto_kem_keypair_derand/cbmc-proof.txt
new file mode 100644
index 000000000..3d1913ebf
--- /dev/null
+++ b/cbmc/proofs/crypto_kem_keypair_derand/cbmc-proof.txt
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: Apache-2.0
+
+# This file marks this directory as containing a CBMC proof.
diff --git a/cbmc/proofs/crypto_kem_keypair_derand/crypto_kem_keypair_derand_harness.c b/cbmc/proofs/crypto_kem_keypair_derand/crypto_kem_keypair_derand_harness.c
new file mode 100644
index 000000000..be09d867f
--- /dev/null
+++ b/cbmc/proofs/crypto_kem_keypair_derand/crypto_kem_keypair_derand_harness.c
@@ -0,0 +1,27 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: MIT-0
+
+/*
+ * Insert copyright notice
+ */
+
+/**
+ * @file crypto_kem_keypair_derand_harness.c
+ * @brief Implements the proof harness for crypto_kem_keypair_derand function.
+ */
+
+/*
+ * Insert project header files that
+ *   - include the declaration of the function
+ *   - include the types needed to declare function arguments
+ */
+#include <kem.h>
+
+/**
+ * @brief Starting point for formal analysis
+ *
+ */
+void harness(void) {
+  uint8_t *a, *b, *c;
+  crypto_kem_keypair_derand(a, b, c);
+}
diff --git a/mlkem/kem.h b/mlkem/kem.h
index e79e9a539..039f9e27e 100644
--- a/mlkem/kem.h
+++ b/mlkem/kem.h
@@ -3,6 +3,7 @@
 #define KEM_H
 
 #include <stdint.h>
+#include "cbmc.h"
 #include "params.h"
 
 #define CRYPTO_SECRETKEYBYTES MLKEM_SECRETKEYBYTES
@@ -19,7 +20,14 @@
 #endif
 
 #define crypto_kem_keypair_derand MLKEM_NAMESPACE(keypair_derand)
-int crypto_kem_keypair_derand(uint8_t *pk, uint8_t *sk, const uint8_t *coins);
+int crypto_kem_keypair_derand(uint8_t *pk, uint8_t *sk, const uint8_t *coins)
+    // clang-format off
+  REQUIRES(IS_FRESH(pk, MLKEM_PUBLICKEYBYTES))
+  REQUIRES(IS_FRESH(sk, MLKEM_SECRETKEYBYTES))
+  REQUIRES(IS_FRESH(coins, 2 * MLKEM_SYMBYTES))
+  ASSIGNS(OBJECT_WHOLE(pk))
+  ASSIGNS(OBJECT_WHOLE(sk));
+// clang-format on
 
 #define crypto_kem_keypair MLKEM_NAMESPACE(keypair)
 int crypto_kem_keypair(uint8_t *pk, uint8_t *sk);