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Add secp256k1_tagged_sha256 as defined in BIP-340

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Gives users the ability to hash messages to 32 byte before they are signed while
allowing efficient domain separation through the tag.
This commit is contained in:
Jonas Nick 2021-01-15 20:58:01 +00:00
parent b6c0b72fb0
commit 5a8e4991ad
3 changed files with 71 additions and 0 deletions
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25
include/secp256k1.h
View File

@ -793,6 +793,31 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_combine(
size_t n
) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
/** Compute a tagged hash as defined in BIP-340.
*
* This is useful for creating a message hash and achieving domain separation
* through an application-specific tag. This function returns
* SHA256(SHA256(tag)||SHA256(tag)||msg). Therefore, tagged hash
* implementations optimized for a specific tag can precompute the SHA256 state
* after hashing the tag hashes.
*
* Returns 0 if the arguments are invalid and 1 otherwise.
* Args: ctx: pointer to a context object
* Out: hash32: pointer to a 32-byte array to store the resulting hash
* In: tag: pointer to an array containing the tag
* taglen: length of the tag array
* msg: pointer to an array containing the message
* msglen: length of the message array
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_tagged_sha256(
const secp256k1_context* ctx,
unsigned char *hash32,
const unsigned char *tag,
size_t taglen,
const unsigned char *msg,
size_t msglen
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(5);
#ifdef __cplusplus
}
#endif

13
src/secp256k1.c
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@ -790,6 +790,19 @@ int secp256k1_ec_pubkey_combine(const secp256k1_context* ctx, secp256k1_pubkey *
return 1;
}
int secp256k1_tagged_sha256(const secp256k1_context* ctx, unsigned char *hash32, const unsigned char *tag, size_t taglen, const unsigned char *msg, size_t msglen) {
secp256k1_sha256 sha;
VERIFY_CHECK(ctx != NULL);
ARG_CHECK(hash32 != NULL);
ARG_CHECK(tag != NULL);
ARG_CHECK(msg != NULL);
secp256k1_sha256_initialize_tagged(&sha, tag, taglen);
secp256k1_sha256_write(&sha, msg, msglen);
secp256k1_sha256_finalize(&sha, hash32);
return 1;
}
#ifdef ENABLE_MODULE_ECDH
# include "modules/ecdh/main_impl.h"
#endif

33
src/tests.c
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@ -564,6 +564,38 @@ void run_rfc6979_hmac_sha256_tests(void) {
secp256k1_rfc6979_hmac_sha256_finalize(&rng);
}
void run_tagged_sha256_tests(void) {
int ecount = 0;
secp256k1_context *none = secp256k1_context_create(SECP256K1_CONTEXT_NONE);
unsigned char tag[32] = { 0 };
unsigned char msg[32] = { 0 };
unsigned char hash32[32];
unsigned char hash_expected[32] = {
0x04, 0x7A, 0x5E, 0x17, 0xB5, 0x86, 0x47, 0xC1,
0x3C, 0xC6, 0xEB, 0xC0, 0xAA, 0x58, 0x3B, 0x62,
0xFB, 0x16, 0x43, 0x32, 0x68, 0x77, 0x40, 0x6C,
0xE2, 0x76, 0x55, 0x9A, 0x3B, 0xDE, 0x55, 0xB3
};
secp256k1_context_set_illegal_callback(none, counting_illegal_callback_fn, &ecount);
/* API test */
CHECK(secp256k1_tagged_sha256(none, hash32, tag, sizeof(tag), msg, sizeof(msg)) == 1);
CHECK(secp256k1_tagged_sha256(none, NULL, tag, sizeof(tag), msg, sizeof(msg)) == 0);
CHECK(ecount == 1);
CHECK(secp256k1_tagged_sha256(none, hash32, NULL, 0, msg, sizeof(msg)) == 0);
CHECK(ecount == 2);
CHECK(secp256k1_tagged_sha256(none, hash32, tag, sizeof(tag), NULL, 0) == 0);
CHECK(ecount == 3);
/* Static test vector */
memcpy(tag, "tag", 3);
memcpy(msg, "msg", 3);
CHECK(secp256k1_tagged_sha256(none, hash32, tag, 3, msg, 3) == 1);
CHECK(secp256k1_memcmp_var(hash32, hash_expected, sizeof(hash32)) == 0);
secp256k1_context_destroy(none);
}
/***** RANDOM TESTS *****/
void test_rand_bits(int rand32, int bits) {
@ -6505,6 +6537,7 @@ int main(int argc, char **argv) {
run_sha256_tests();
run_hmac_sha256_tests();
run_rfc6979_hmac_sha256_tests();
run_tagged_sha256_tests();
/* scalar tests */
run_scalar_tests();