From 0d9561ae879848191a14bcc67db87cbfd44fb69a Mon Sep 17 00:00:00 2001 From: Andrew Poelstra Date: Sun, 22 Nov 2020 17:33:46 +0000 Subject: [PATCH] add `secp256k1_ec_pubkey_cmp` method --- include/secp256k1.h | 20 ++++++++++++++++-- src/secp256k1.c | 26 +++++++++++++++++++++++ src/tests.c | 50 +++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 94 insertions(+), 2 deletions(-) diff --git a/include/secp256k1.h b/include/secp256k1.h index d368488af21c4..54eff5501dabb 100644 --- a/include/secp256k1.h +++ b/include/secp256k1.h @@ -61,8 +61,9 @@ typedef struct secp256k1_scratch_space_struct secp256k1_scratch_space; * The exact representation of data inside is implementation defined and not * guaranteed to be portable between different platforms or versions. It is * however guaranteed to be 64 bytes in size, and can be safely copied/moved. - * If you need to convert to a format suitable for storage, transmission, or - * comparison, use secp256k1_ec_pubkey_serialize and secp256k1_ec_pubkey_parse. + * If you need to convert to a format suitable for storage or transmission, + * use secp256k1_ec_pubkey_serialize and secp256k1_ec_pubkey_parse. To + * compare keys, use secp256k1_ec_pubkey_cmp. */ typedef struct { unsigned char data[64]; @@ -370,6 +371,21 @@ SECP256K1_API int secp256k1_ec_pubkey_serialize( unsigned int flags ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4); +/** Compare two public keys using lexicographic (of compressed serialization) order + * + * Returns: <0 if the first public key is less than the second + * >0 if the first public key is greater than the second + * 0 if the two public keys are equal + * Args: ctx: a secp256k1 context object. + * In: pubkey1: first public key to compare + * pubkey2: second public key to compare + */ +SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_cmp( + const secp256k1_context* ctx, + const secp256k1_pubkey* pubkey1, + const secp256k1_pubkey* pubkey2 +) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3); + /** Parse an ECDSA signature in compact (64 bytes) format. * * Returns: 1 when the signature could be parsed, 0 otherwise. diff --git a/src/secp256k1.c b/src/secp256k1.c index aef3f99ac3b39..515bcb93db20e 100644 --- a/src/secp256k1.c +++ b/src/secp256k1.c @@ -316,6 +316,32 @@ int secp256k1_ec_pubkey_serialize(const secp256k1_context* ctx, unsigned char *o return ret; } +int secp256k1_ec_pubkey_cmp(const secp256k1_context* ctx, const secp256k1_pubkey* pubkey0, const secp256k1_pubkey* pubkey1) { + unsigned char out[2][33]; + const secp256k1_pubkey* pk[2]; + int i; + + VERIFY_CHECK(ctx != NULL); + pk[0] = pubkey0; pk[1] = pubkey1; + for (i = 0; i < 2; i++) { + size_t out_size = sizeof(out[i]); + /* If the public key is NULL or invalid, ec_pubkey_serialize will call + * the illegal_callback and return 0. In that case we will serialize the + * key as all zeros which is less than any valid public key. This + * results in consistent comparisons even if NULL or invalid pubkeys are + * involved and prevents edge cases such as sorting algorithms that use + * this function and do not terminate as a result. */ + if (!secp256k1_ec_pubkey_serialize(ctx, out[i], &out_size, pk[i], SECP256K1_EC_COMPRESSED)) { + /* Note that ec_pubkey_serialize should already set the output to + * zero in that case, but it's not guaranteed by the API, we can't + * test it and writing a VERIFY_CHECK is more complex than + * explicitly memsetting (again). */ + memset(out[i], 0, sizeof(out[i])); + } + } + return secp256k1_memcmp_var(out[0], out[1], sizeof(out[0])); +} + static void secp256k1_ecdsa_signature_load(const secp256k1_context* ctx, secp256k1_scalar* r, secp256k1_scalar* s, const secp256k1_ecdsa_signature* sig) { (void)ctx; if (sizeof(secp256k1_scalar) == 32) { diff --git a/src/tests.c b/src/tests.c index f19ab96e386a3..c901143c6c9f0 100644 --- a/src/tests.c +++ b/src/tests.c @@ -4809,6 +4809,55 @@ void test_random_pubkeys(void) { } } +void run_pubkey_comparison(void) { + unsigned char pk1_ser[33] = { + 0x02, + 0x58, 0x84, 0xb3, 0xa2, 0x4b, 0x97, 0x37, 0x88, 0x92, 0x38, 0xa6, 0x26, 0x62, 0x52, 0x35, 0x11, + 0xd0, 0x9a, 0xa1, 0x1b, 0x80, 0x0b, 0x5e, 0x93, 0x80, 0x26, 0x11, 0xef, 0x67, 0x4b, 0xd9, 0x23 + }; + const unsigned char pk2_ser[33] = { + 0x02, + 0xde, 0x36, 0x0e, 0x87, 0x59, 0x8f, 0x3c, 0x01, 0x36, 0x2a, 0x2a, 0xb8, 0xc6, 0xf4, 0x5e, 0x4d, + 0xb2, 0xc2, 0xd5, 0x03, 0xa7, 0xf9, 0xf1, 0x4f, 0xa8, 0xfa, 0x95, 0xa8, 0xe9, 0x69, 0x76, 0x1c + }; + secp256k1_pubkey pk1; + secp256k1_pubkey pk2; + int32_t ecount = 0; + + CHECK(secp256k1_ec_pubkey_parse(ctx, &pk1, pk1_ser, sizeof(pk1_ser)) == 1); + CHECK(secp256k1_ec_pubkey_parse(ctx, &pk2, pk2_ser, sizeof(pk2_ser)) == 1); + + secp256k1_context_set_illegal_callback(ctx, counting_illegal_callback_fn, &ecount); + CHECK(secp256k1_ec_pubkey_cmp(ctx, NULL, &pk2) < 0); + CHECK(ecount == 1); + CHECK(secp256k1_ec_pubkey_cmp(ctx, &pk1, NULL) > 0); + CHECK(ecount == 2); + CHECK(secp256k1_ec_pubkey_cmp(ctx, &pk1, &pk2) < 0); + CHECK(secp256k1_ec_pubkey_cmp(ctx, &pk2, &pk1) > 0); + CHECK(secp256k1_ec_pubkey_cmp(ctx, &pk1, &pk1) == 0); + CHECK(secp256k1_ec_pubkey_cmp(ctx, &pk2, &pk2) == 0); + CHECK(ecount == 2); + { + secp256k1_pubkey pk_tmp; + memset(&pk_tmp, 0, sizeof(pk_tmp)); /* illegal pubkey */ + CHECK(secp256k1_ec_pubkey_cmp(ctx, &pk_tmp, &pk2) < 0); + CHECK(ecount == 3); + CHECK(secp256k1_ec_pubkey_cmp(ctx, &pk_tmp, &pk_tmp) == 0); + CHECK(ecount == 5); + CHECK(secp256k1_ec_pubkey_cmp(ctx, &pk2, &pk_tmp) > 0); + CHECK(ecount == 6); + } + + secp256k1_context_set_illegal_callback(ctx, NULL, NULL); + + /* Make pk2 the same as pk1 but with 3 rather than 2. Note that in + * an uncompressed encoding, these would have the opposite ordering */ + pk1_ser[0] = 3; + CHECK(secp256k1_ec_pubkey_parse(ctx, &pk2, pk1_ser, sizeof(pk1_ser)) == 1); + CHECK(secp256k1_ec_pubkey_cmp(ctx, &pk1, &pk2) < 0); + CHECK(secp256k1_ec_pubkey_cmp(ctx, &pk2, &pk1) > 0); +} + void run_random_pubkeys(void) { int i; for (i = 0; i < 10*count; i++) { @@ -5860,6 +5909,7 @@ int main(int argc, char **argv) { #endif /* ecdsa tests */ + run_pubkey_comparison(); run_random_pubkeys(); run_ecdsa_der_parse(); run_ecdsa_sign_verify();