From 3d2302257f19533932cd53547e9745b6283a907d Mon Sep 17 00:00:00 2001 From: Gregory Maxwell Date: Wed, 8 Jan 2020 11:56:15 +0000 Subject: [PATCH] Constant-time behaviour test using valgrind memtest. Valgrind does bit-level tracking of the "uninitialized" status of memory, property tracks memory which is tainted by any uninitialized memory, and warns if any branch or array access depends on an uninitialized bit. That is exactly the verification we need on secret data to test for constant-time behaviour. All we need to do is tell valgrind our secret key is actually uninitialized memory. This adds a valgrind_ctime_test which is compiled if valgrind is installed: Run it with libtool --mode=execute: $ libtool --mode=execute valgrind ./valgrind_ctime_test --- .gitignore | 1 + Makefile.am | 6 +++ configure.ac | 1 + src/valgrind_ctime_test.c | 100 ++++++++++++++++++++++++++++++++++++++ 4 files changed, 108 insertions(+) create mode 100644 src/valgrind_ctime_test.c diff --git a/.gitignore b/.gitignore index 55d325a..cb4331a 100644 --- a/.gitignore +++ b/.gitignore @@ -9,6 +9,7 @@ bench_internal tests exhaustive_tests gen_context +valgrind_ctime_test *.exe *.so *.a diff --git a/Makefile.am b/Makefile.am index 79dcf6e..e73b1ba 100644 --- a/Makefile.am +++ b/Makefile.am @@ -93,6 +93,12 @@ if USE_TESTS noinst_PROGRAMS += tests tests_SOURCES = src/tests.c tests_CPPFLAGS = -DSECP256K1_BUILD -I$(top_srcdir)/src -I$(top_srcdir)/include $(SECP_INCLUDES) $(SECP_TEST_INCLUDES) +if VALGRIND_ENABLED +tests_CPPFLAGS += -DVALGRIND +noinst_PROGRAMS += valgrind_ctime_test +valgrind_ctime_test_SOURCES = src/valgrind_ctime_test.c +valgrind_ctime_test_LDADD = libsecp256k1.la $(SECP_LIBS) $(SECP_TEST_LIBS) $(COMMON_LIB) +endif if !ENABLE_COVERAGE tests_CPPFLAGS += -DVERIFY endif diff --git a/configure.ac b/configure.ac index a2023ab..e4929d6 100644 --- a/configure.ac +++ b/configure.ac @@ -556,6 +556,7 @@ echo " scalar = $set_scalar" echo " ecmult window size = $set_ecmult_window" echo " ecmult gen prec. bits = $set_ecmult_gen_precision" echo +echo " valgrind = $enable_valgrind" echo " CC = $CC" echo " CFLAGS = $CFLAGS" echo " CPPFLAGS = $CPPFLAGS" diff --git a/src/valgrind_ctime_test.c b/src/valgrind_ctime_test.c new file mode 100644 index 0000000..04c06d4 --- /dev/null +++ b/src/valgrind_ctime_test.c @@ -0,0 +1,100 @@ +/********************************************************************** + * Copyright (c) 2020 Gregory Maxwell * + * Distributed under the MIT software license, see the accompanying * + * file COPYING or http://www.opensource.org/licenses/mit-license.php.* + **********************************************************************/ + +#include +#include "include/secp256k1.h" +#include "util.h" + +#if ENABLE_MODULE_ECDH +# include "include/secp256k1_ecdh.h" +#endif + +int main(void) { + secp256k1_context* ctx; + secp256k1_ecdsa_signature signature; + secp256k1_pubkey pubkey; + size_t siglen = 74; + size_t outputlen = 33; + int i; + int ret; + unsigned char msg[32]; + unsigned char key[32]; + unsigned char sig[74]; + unsigned char spubkey[33]; + + if (!RUNNING_ON_VALGRIND) { + fprintf(stderr, "This test can only usefully be run inside valgrind.\n"); + fprintf(stderr, "Usage: libtool --mode=execute valgrind ./valgrind_ctime_test\n"); + exit(1); + } + + /** In theory, testing with a single secret input should be sufficient: + * If control flow depended on secrets the tool would generate an error. + */ + for (i = 0; i < 32; i++) { + key[i] = i + 65; + } + for (i = 0; i < 32; i++) { + msg[i] = i + 1; + } + + ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_DECLASSIFY); + + /* Test keygen. */ + VALGRIND_MAKE_MEM_UNDEFINED(key, 32); + ret = secp256k1_ec_pubkey_create(ctx, &pubkey, key); + VALGRIND_MAKE_MEM_DEFINED(&pubkey, sizeof(secp256k1_pubkey)); + VALGRIND_MAKE_MEM_DEFINED(&ret, sizeof(ret)); + CHECK(ret); + CHECK(secp256k1_ec_pubkey_serialize(ctx, spubkey, &outputlen, &pubkey, SECP256K1_EC_COMPRESSED) == 1); + + /* Test signing. */ + VALGRIND_MAKE_MEM_UNDEFINED(key, 32); + ret = secp256k1_ecdsa_sign(ctx, &signature, msg, key, NULL, NULL); + VALGRIND_MAKE_MEM_DEFINED(&signature, sizeof(secp256k1_ecdsa_signature)); + VALGRIND_MAKE_MEM_DEFINED(&ret, sizeof(ret)); + CHECK(ret); + CHECK(secp256k1_ecdsa_signature_serialize_der(ctx, sig, &siglen, &signature)); + +#if ENABLE_MODULE_ECDH + /* Test ECDH. */ + VALGRIND_MAKE_MEM_UNDEFINED(key, 32); + ret = secp256k1_ecdh(ctx, msg, &pubkey, key, NULL, NULL); + VALGRIND_MAKE_MEM_DEFINED(&ret, sizeof(ret)); + CHECK(ret == 1); +#endif + + VALGRIND_MAKE_MEM_UNDEFINED(key, 32); + ret = secp256k1_ec_seckey_verify(ctx, key); + VALGRIND_MAKE_MEM_DEFINED(&ret, sizeof(ret)); + CHECK(ret == 1); + + VALGRIND_MAKE_MEM_UNDEFINED(key, 32); + ret = secp256k1_ec_privkey_negate(ctx, key); + VALGRIND_MAKE_MEM_DEFINED(&ret, sizeof(ret)); + CHECK(ret == 1); + + VALGRIND_MAKE_MEM_UNDEFINED(key, 32); + VALGRIND_MAKE_MEM_UNDEFINED(msg, 32); + ret = secp256k1_ec_privkey_tweak_add(ctx, key, msg); + VALGRIND_MAKE_MEM_DEFINED(&ret, sizeof(ret)); + CHECK(ret == 1); + + VALGRIND_MAKE_MEM_UNDEFINED(key, 32); + VALGRIND_MAKE_MEM_UNDEFINED(msg, 32); + ret = secp256k1_ec_privkey_tweak_mul(ctx, key, msg); + VALGRIND_MAKE_MEM_DEFINED(&ret, sizeof(ret)); + CHECK(ret == 1); + + /* Test context randomisation. Do this last because it leaves the context tainted. */ + VALGRIND_MAKE_MEM_UNDEFINED(key, 32); + ret = secp256k1_context_randomize(ctx, key); + VALGRIND_MAKE_MEM_DEFINED(&ret, sizeof(ret)); + CHECK(ret); + + secp256k1_context_destroy(ctx); + return 0; +}