diff --git a/include/secp256k1.h b/include/secp256k1.h index dca7ca00..00129e7d 100644 --- a/include/secp256k1.h +++ b/include/secp256k1.h @@ -77,40 +77,64 @@ SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdsa_verify( int pubkeylen ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(4); +/** A pointer to a function to deterministically generate a nonce. + * Returns: 1 if a nonce was succesfully generated. 0 will cause signing to fail. + * In: msg32: the 32-byte message hash being verified (will not be NULL) + * key32: pointer to a 32-byte secret key (will not be NULL) + * attempt: how many iterations we have tried to find a nonce. + * This will almost always be 0, but different attempt values + * are required to result in a different nonce. + * data: Arbitrary data pointer that is passed through. + * Out: nonce32: pointer to a 32-byte array to be filled by the function. + * Except for test cases, this function should compute some cryptographic hash of + * the message, the key and the attempt. It is advised to use RFC6979. + */ +typedef int (*secp256k1_nonce_function_t)( + unsigned char *nonce32, + const unsigned char *msg32, + const unsigned char *key32, + unsigned int attempt, + const void *data +); + /** Create an ECDSA signature. * Returns: 1: signature created - * 0: nonce invalid, try another one + * 0: the nonce generation function failed * In: msg32: the 32-byte message hash being signed (cannot be NULL) * seckey: pointer to a 32-byte secret key (cannot be NULL, assumed to be valid) - * nonce: pointer to a 32-byte nonce (cannot be NULL, generated with a cryptographic PRNG) + * noncefp:pointer to a nonce generation function (cannot be NULL) + * ndata: pointer to arbitrary data used by the nonce generation function (can be NULL) * Out: sig: pointer to an array where the signature will be placed (cannot be NULL) * In/Out: siglen: pointer to an int with the length of sig, which will be updated * to contain the actual signature length (<=72). * Requires starting using SECP256K1_START_SIGN. */ -SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdsa_sign( +int secp256k1_ecdsa_sign( const unsigned char *msg32, unsigned char *sig, int *siglen, const unsigned char *seckey, - const unsigned char *nonce + secp256k1_nonce_function_t noncefp, + const void *ndata ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4) SECP256K1_ARG_NONNULL(5); /** Create a compact ECDSA signature (64 byte + recovery id). * Returns: 1: signature created - * 0: nonce invalid, try another one + * 0: the nonce generation function failed * In: msg32: the 32-byte message hash being signed (cannot be NULL) * seckey: pointer to a 32-byte secret key (cannot be NULL, assumed to be valid) - * nonce: pointer to a 32-byte nonce (cannot be NULL, generated with a cryptographic PRNG) + * noncefp:pointer to a nonce generation function (cannot be NULL) + * ndata: pointer to arbitrary data used by the nonce generation function (can be NULL) * Out: sig: pointer to a 64-byte array where the signature will be placed (cannot be NULL) * recid: pointer to an int, which will be updated to contain the recovery id (can be NULL) * Requires starting using SECP256K1_START_SIGN. */ -SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdsa_sign_compact( +int secp256k1_ecdsa_sign_compact( const unsigned char *msg32, unsigned char *sig64, const unsigned char *seckey, - const unsigned char *nonce, + secp256k1_nonce_function_t noncefp, + const void *ndata, int *recid ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4); diff --git a/src/bench_sign.c b/src/bench_sign.c index 66e71e1a..e4cb36c3 100644 --- a/src/bench_sign.c +++ b/src/bench_sign.c @@ -10,15 +10,22 @@ typedef struct { unsigned char msg[32]; - unsigned char nonce[32]; unsigned char key[32]; } bench_sign_t; +/** Very fast but insecure nonce generation function. Do not use for production code. */ +static int insecure_nonce_function(unsigned char *nonce32, const unsigned char *msg32, const unsigned char *key32, unsigned int count, const void *data) { + (void)data; + for (int i = 0; i < 8; i++) { + ((uint32_t*)nonce32)[i] = ((uint32_t*)msg32)[i] + ((uint32_t*)key32)[i] + count; + } + return 1; +} + static void bench_sign_setup(void* arg) { bench_sign_t *data = (bench_sign_t*)arg; for (int i = 0; i < 32; i++) data->msg[i] = i + 1; - for (int i = 0; i < 32; i++) data->nonce[i] = i + 33; for (int i = 0; i < 32; i++) data->key[i] = i + 65; } @@ -28,9 +35,8 @@ static void bench_sign(void* arg) { unsigned char sig[64]; for (int i=0; i<20000; i++) { int recid = 0; - CHECK(secp256k1_ecdsa_sign_compact(data->msg, sig, data->key, data->nonce, &recid)); + secp256k1_ecdsa_sign_compact(data->msg, sig, data->key, insecure_nonce_function, NULL, &recid); for (int j = 0; j < 32; j++) { - data->nonce[j] = data->key[j]; /* Move former key to nonce */ data->msg[j] = sig[j]; /* Move former R to message. */ data->key[j] = sig[j + 32]; /* Move former S to key. */ } diff --git a/src/bench_verify.c b/src/bench_verify.c index b123c408..c3d1c39d 100644 --- a/src/bench_verify.c +++ b/src/bench_verify.c @@ -14,13 +14,21 @@ typedef struct { unsigned char msg[32]; unsigned char key[32]; - unsigned char nonce[32]; unsigned char sig[72]; int siglen; unsigned char pubkey[33]; int pubkeylen; } benchmark_verify_t; +/** Very fast but insecure nonce generation function. Do not use for production code. */ +static int insecure_nonce_function(unsigned char *nonce32, const unsigned char *msg32, const unsigned char *key32, unsigned int count, const void *data) { + (void)data; + for (int i = 0; i < 8; i++) { + ((uint32_t*)nonce32)[i] = ((uint32_t*)msg32)[i] + ((uint32_t*)key32)[i] + count; + } + return 1; +} + static void benchmark_verify(void* arg) { benchmark_verify_t* data = (benchmark_verify_t*)arg; @@ -42,9 +50,8 @@ int main(void) { for (int i = 0; i < 32; i++) data.msg[i] = 1 + i; for (int i = 0; i < 32; i++) data.key[i] = 33 + i; - for (int i = 0; i < 32; i++) data.nonce[i] = 65 + i; data.siglen = 72; - CHECK(secp256k1_ecdsa_sign(data.msg, data.sig, &data.siglen, data.key, data.nonce)); + secp256k1_ecdsa_sign(data.msg, data.sig, &data.siglen, data.key, insecure_nonce_function, NULL); data.pubkeylen = 33; CHECK(secp256k1_ec_pubkey_create(data.pubkey, &data.pubkeylen, data.key, 1)); diff --git a/src/secp256k1.c b/src/secp256k1.c index 4fb2d0aa..d1db6460 100644 --- a/src/secp256k1.c +++ b/src/secp256k1.c @@ -69,23 +69,35 @@ end: return ret; } -int secp256k1_ecdsa_sign(const unsigned char *msg32, unsigned char *signature, int *signaturelen, const unsigned char *seckey, const unsigned char *nonce) { +int secp256k1_ecdsa_sign(const unsigned char *msg32, unsigned char *signature, int *signaturelen, const unsigned char *seckey, secp256k1_nonce_function_t noncefp, const void* noncedata) { DEBUG_CHECK(secp256k1_ecmult_gen_consts != NULL); DEBUG_CHECK(msg32 != NULL); DEBUG_CHECK(signature != NULL); DEBUG_CHECK(signaturelen != NULL); DEBUG_CHECK(seckey != NULL); - DEBUG_CHECK(nonce != NULL); + DEBUG_CHECK(noncefp != NULL); secp256k1_scalar_t sec, non, msg; secp256k1_scalar_set_b32(&sec, seckey, NULL); - int overflow = 0; - secp256k1_scalar_set_b32(&non, nonce, &overflow); secp256k1_scalar_set_b32(&msg, msg32, NULL); - int ret = !secp256k1_scalar_is_zero(&non) && !overflow; + int overflow = 0; + int ret = 0; + unsigned int count = 0; secp256k1_ecdsa_sig_t sig; - if (ret) { - ret = secp256k1_ecdsa_sig_sign(&sig, &sec, &msg, &non, NULL); + while (1) { + unsigned char nonce32[32]; + ret = noncefp(nonce32, msg32, seckey, count, noncedata); + if (!ret) { + break; + } + secp256k1_scalar_set_b32(&non, nonce32, &overflow); + memset(nonce32, 0, 32); + if (!secp256k1_scalar_is_zero(&non) && !overflow) { + if (secp256k1_ecdsa_sig_sign(&sig, &sec, &msg, &non, NULL)) { + break; + } + } + count++; } if (ret) { ret = secp256k1_ecdsa_sig_serialize(signature, signaturelen, &sig); @@ -96,22 +108,34 @@ int secp256k1_ecdsa_sign(const unsigned char *msg32, unsigned char *signature, i return ret; } -int secp256k1_ecdsa_sign_compact(const unsigned char *msg32, unsigned char *sig64, const unsigned char *seckey, const unsigned char *nonce, int *recid) { +int secp256k1_ecdsa_sign_compact(const unsigned char *msg32, unsigned char *sig64, const unsigned char *seckey, secp256k1_nonce_function_t noncefp, const void* noncedata, int *recid) { DEBUG_CHECK(secp256k1_ecmult_gen_consts != NULL); DEBUG_CHECK(msg32 != NULL); DEBUG_CHECK(sig64 != NULL); DEBUG_CHECK(seckey != NULL); - DEBUG_CHECK(nonce != NULL); + DEBUG_CHECK(noncefp != NULL); secp256k1_scalar_t sec, non, msg; secp256k1_scalar_set_b32(&sec, seckey, NULL); - int overflow = 0; - secp256k1_scalar_set_b32(&non, nonce, &overflow); secp256k1_scalar_set_b32(&msg, msg32, NULL); - int ret = !secp256k1_scalar_is_zero(&non) && !overflow; + int overflow = 0; + int ret = 0; + unsigned int count = 0; secp256k1_ecdsa_sig_t sig; - if (ret) { - ret = secp256k1_ecdsa_sig_sign(&sig, &sec, &msg, &non, recid); + while (1) { + unsigned char nonce32[32]; + ret = noncefp(nonce32, msg32, seckey, count, noncedata); + if (!ret) { + break; + } + secp256k1_scalar_set_b32(&non, nonce32, &overflow); + memset(nonce32, 0, 32); + if (!secp256k1_scalar_is_zero(&non) && !overflow) { + if (secp256k1_ecdsa_sig_sign(&sig, &sec, &msg, &non, recid)) { + break; + } + } + count++; } if (ret) { secp256k1_scalar_get_b32(sig64, &sig.r); diff --git a/src/tests.c b/src/tests.c index 8ba1f286..8b2b223e 100644 --- a/src/tests.c +++ b/src/tests.c @@ -949,6 +949,23 @@ void run_ecdsa_sign_verify(void) { } } +/** Very fast but insecure nonce generation function. Do not use for production code. */ +static int insecure_nonce_function(unsigned char *nonce32, const unsigned char *msg32, const unsigned char *key32, unsigned int counter, const void *data) { + (void)data; + for (int i = 0; i < 8; i++) { + ((uint32_t*)nonce32)[i] = ((uint32_t*)msg32)[i] + ((uint32_t*)key32)[i] + counter; + } + return 1; +} + +/** Dummy nonce generation function that just uses a precomputed nonce, and fails if it is not accepted. Use only for testing. */ +static int precomputed_nonce_function(unsigned char *nonce32, const unsigned char *msg32, const unsigned char *key32, unsigned int counter, const void *data) { + (void)msg32; + (void)key32; + memcpy(nonce32, data, 32); + return (counter == 0); +} + void test_ecdsa_end_to_end(void) { unsigned char privkey[32]; unsigned char message[32]; @@ -1006,13 +1023,7 @@ void test_ecdsa_end_to_end(void) { /* Sign. */ unsigned char signature[72]; int signaturelen = 72; - while(1) { - unsigned char rnd[32]; - secp256k1_rand256_test(rnd); - if (secp256k1_ecdsa_sign(message, signature, &signaturelen, privkey, rnd) == 1) { - break; - } - } + CHECK(secp256k1_ecdsa_sign(message, signature, &signaturelen, privkey, insecure_nonce_function, NULL) == 1); /* Verify. */ CHECK(secp256k1_ecdsa_verify(message, signature, signaturelen, pubkey, pubkeylen) == 1); /* Destroy signature and verify again. */ @@ -1021,13 +1032,7 @@ void test_ecdsa_end_to_end(void) { /* Compact sign. */ unsigned char csignature[64]; int recid = 0; - while(1) { - unsigned char rnd[32]; - secp256k1_rand256_test(rnd); - if (secp256k1_ecdsa_sign_compact(message, csignature, privkey, rnd, &recid) == 1) { - break; - } - } + CHECK(secp256k1_ecdsa_sign_compact(message, csignature, privkey, insecure_nonce_function, NULL, &recid) == 1); /* Recover. */ unsigned char recpubkey[65]; int recpubkeylen = 0; CHECK(secp256k1_ecdsa_recover_compact(message, csignature, recpubkey, &recpubkeylen, pubkeylen == 33, recid) == 1); @@ -1294,12 +1299,12 @@ void test_ecdsa_edge_cases(void) { }; unsigned char sig[72]; int siglen = 72; - CHECK(secp256k1_ecdsa_sign(msg, sig, &siglen, key, nonce) == 0); + CHECK(secp256k1_ecdsa_sign(msg, sig, &siglen, key, precomputed_nonce_function, nonce) == 0); msg[31] = 0xaa; siglen = 72; - CHECK(secp256k1_ecdsa_sign(msg, sig, &siglen, key, nonce) == 1); + CHECK(secp256k1_ecdsa_sign(msg, sig, &siglen, key, precomputed_nonce_function, nonce) == 1); siglen = 10; - CHECK(secp256k1_ecdsa_sign(msg, sig, &siglen, key, nonce) != 1); + CHECK(secp256k1_ecdsa_sign(msg, sig, &siglen, key, precomputed_nonce_function, nonce) != 1); } /* Privkey export where pubkey is the point at infinity. */