Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Make aux_rnd32==NULL behave identical to 0x0000..00. #1002

Merged
merged 1 commit into from
Oct 31, 2021
Merged

Make aux_rnd32==NULL behave identical to 0x0000..00. #1002

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
3 changes: 2 additions & 1 deletion include/secp256k1_schnorrsig.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -111,7 +111,8 @@ typedef struct {
* In: msg32: the 32-byte message being signed.
* keypair: pointer to an initialized keypair.
* aux_rand32: 32 bytes of fresh randomness. While recommended to provide
* this, it is only supplemental to security and can be NULL. See
* this, it is only supplemental to security and can be NULL. A
* NULL argument is treated the same as an all-zero one. See
* BIP-340 "Default Signing" for a full explanation of this
* argument and for guidance if randomness is expensive.
*/
Expand Down
19 changes: 13 additions & 6 deletions src/modules/schnorrsig/main_impl.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -65,6 +65,17 @@ static int nonce_function_bip340(unsigned char *nonce32, const unsigned char *ms
for (i = 0; i < 32; i++) {
masked_key[i] ^= key32[i];
}
} else {
/* Precomputed TaggedHash("BIP0340/aux", 0x0000...00); */
static const unsigned char ZERO_MASK[32] = {
84, 241, 105, 207, 201, 226, 229, 114,
116, 128, 68, 31, 144, 186, 37, 196,
136, 244, 97, 199, 11, 94, 165, 220,
170, 247, 175, 105, 39, 10, 165, 20
};
for (i = 0; i < 32; i++) {
masked_key[i] = key32[i] ^ ZERO_MASK[i];
}
}

/* Tag the hash with algo which is important to avoid nonce reuse across
Expand All @@ -77,12 +88,8 @@ static int nonce_function_bip340(unsigned char *nonce32, const unsigned char *ms
secp256k1_sha256_initialize_tagged(&sha, algo, algolen);
}

/* Hash (masked-)key||pk||msg using the tagged hash as per the spec */
if (data != NULL) {
secp256k1_sha256_write(&sha, masked_key, 32);
} else {
secp256k1_sha256_write(&sha, key32, 32);
}
/* Hash masked-key||pk||msg using the tagged hash as per the spec */
secp256k1_sha256_write(&sha, masked_key, 32);
secp256k1_sha256_write(&sha, xonly_pk32, 32);
secp256k1_sha256_write(&sha, msg, msglen);
secp256k1_sha256_finalize(&sha, nonce32);
Expand Down
7 changes: 5 additions & 2 deletions src/modules/schnorrsig/tests_impl.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,7 @@ void run_nonce_function_bip340_tests(void) {
size_t algolen = sizeof(algo);
secp256k1_sha256 sha;
secp256k1_sha256 sha_optimized;
unsigned char nonce[32];
unsigned char nonce[32], nonce_z[32];
unsigned char msg[32];
size_t msglen = sizeof(msg);
unsigned char key[32];
Expand Down Expand Up @@ -107,8 +107,11 @@ void run_nonce_function_bip340_tests(void) {
CHECK(secp256k1_memcmp_var(nonce, nonce2, 32) != 0);
}

/* NULL aux_rand argument is allowed. */
/* NULL aux_rand argument is allowed, and identical to passing all zero aux_rand. */
memset(aux_rand, 0, 32);
CHECK(nonce_function_bip340(nonce_z, msg, msglen, key, pk, algo, algolen, &aux_rand) == 1);
CHECK(nonce_function_bip340(nonce, msg, msglen, key, pk, algo, algolen, NULL) == 1);
CHECK(secp256k1_memcmp_var(nonce_z, nonce, 32) == 0);
}

void test_schnorrsig_api(void) {
Expand Down