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hash: add midstate initializer and use it for tagged hashes

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Introduce secp256k1_sha256_initialize_midstate() in the hash layer and use it at all tagged-hash midstate call sites across schnorrsig, musig, and ellswift.

Document the byte-counter contract at the declaration site in hash.h and add run_sha256_initialize_midstate_tests() to directly verify helper behavior against initialize_tagged.

Also switch the helper to take const uint32_t state[8] to reduce argument-order risk at call sites.
This commit is contained in:
w0xlt
2026-02-18 15:21:54 -08:00
parent 471e3a130d
commit f48b1bfa5d
7 changed files with 80 additions and 118 deletions
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48
src/modules/ellswift/main_impl.h
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@@ -383,17 +383,11 @@ static void secp256k1_ellswift_elligatorswift_var(unsigned char *u32, secp256k1_
/** Set hash state to the BIP340 tagged hash midstate for "secp256k1_ellswift_encode". */
static void secp256k1_ellswift_sha256_init_encode(secp256k1_sha256* hash) {
secp256k1_sha256_initialize(hash);
hash->s[0] = 0xd1a6524bul;
hash->s[1] = 0x028594b3ul;
hash->s[2] = 0x96e42f4eul;
hash->s[3] = 0x1037a177ul;
hash->s[4] = 0x1b8fcb8bul;
hash->s[5] = 0x56023885ul;
hash->s[6] = 0x2560ede1ul;
hash->s[7] = 0xd626b715ul;
hash->bytes = 64;
static const uint32_t midstate[8] = {
0xd1a6524bul, 0x028594b3ul, 0x96e42f4eul, 0x1037a177ul,
0x1b8fcb8bul, 0x56023885ul, 0x2560ede1ul, 0xd626b715ul
};
secp256k1_sha256_initialize_midstate(hash, 64, midstate);
}
int secp256k1_ellswift_encode(const secp256k1_context *ctx, unsigned char *ell64, const secp256k1_pubkey *pubkey, const unsigned char *rnd32) {
@@ -427,17 +421,11 @@ int secp256k1_ellswift_encode(const secp256k1_context *ctx, unsigned char *ell64
/** Set hash state to the BIP340 tagged hash midstate for "secp256k1_ellswift_create". */
static void secp256k1_ellswift_sha256_init_create(secp256k1_sha256* hash) {
secp256k1_sha256_initialize(hash);
hash->s[0] = 0xd29e1bf5ul;
hash->s[1] = 0xf7025f42ul;
hash->s[2] = 0x9b024773ul;
hash->s[3] = 0x094cb7d5ul;
hash->s[4] = 0xe59ed789ul;
hash->s[5] = 0x03bc9786ul;
hash->s[6] = 0x68335b35ul;
hash->s[7] = 0x4e363b53ul;
hash->bytes = 64;
static const uint32_t midstate[8] = {
0xd29e1bf5ul, 0xf7025f42ul, 0x9b024773ul, 0x094cb7d5ul,
0xe59ed789ul, 0x03bc9786ul, 0x68335b35ul, 0x4e363b53ul
};
secp256k1_sha256_initialize_midstate(hash, 64, midstate);
}
int secp256k1_ellswift_create(const secp256k1_context *ctx, unsigned char *ell64, const unsigned char *seckey32, const unsigned char *auxrnd32) {
@@ -510,17 +498,11 @@ static int ellswift_xdh_hash_function_prefix(unsigned char *output, const unsign
/** Set hash state to the BIP340 tagged hash midstate for "bip324_ellswift_xonly_ecdh". */
static void secp256k1_ellswift_sha256_init_bip324(secp256k1_sha256* hash) {
secp256k1_sha256_initialize(hash);
hash->s[0] = 0x8c12d730ul;
hash->s[1] = 0x827bd392ul;
hash->s[2] = 0x9e4fb2eeul;
hash->s[3] = 0x207b373eul;
hash->s[4] = 0x2292bd7aul;
hash->s[5] = 0xaa5441bcul;
hash->s[6] = 0x15c3779ful;
hash->s[7] = 0xcfb52549ul;
hash->bytes = 64;
static const uint32_t midstate[8] = {
0x8c12d730ul, 0x827bd392ul, 0x9e4fb2eeul, 0x207b373eul,
0x2292bd7aul, 0xaa5441bcul, 0x15c3779ful, 0xcfb52549ul
};
secp256k1_sha256_initialize_midstate(hash, 64, midstate);
}
static int ellswift_xdh_hash_function_bip324(unsigned char* output, const unsigned char *x32, const unsigned char *ell_a64, const unsigned char *ell_b64, void *data) {

32
src/modules/musig/keyagg_impl.h
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@@ -62,17 +62,11 @@ static int secp256k1_keyagg_cache_load(const secp256k1_context* ctx, secp256k1_k
/* Initializes SHA256 with fixed midstate. This midstate was computed by applying
* SHA256 to SHA256("KeyAgg list")||SHA256("KeyAgg list"). */
static void secp256k1_musig_keyagglist_sha256(secp256k1_sha256 *sha) {
secp256k1_sha256_initialize(sha);
sha->s[0] = 0xb399d5e0ul;
sha->s[1] = 0xc8fff302ul;
sha->s[2] = 0x6badac71ul;
sha->s[3] = 0x07c5b7f1ul;
sha->s[4] = 0x9701e2eful;
sha->s[5] = 0x2a72ecf8ul;
sha->s[6] = 0x201a4c7bul;
sha->s[7] = 0xab148a38ul;
sha->bytes = 64;
static const uint32_t midstate[8] = {
0xb399d5e0ul, 0xc8fff302ul, 0x6badac71ul, 0x07c5b7f1ul,
0x9701e2eful, 0x2a72ecf8ul, 0x201a4c7bul, 0xab148a38ul
};
secp256k1_sha256_initialize_midstate(sha, 64, midstate);
}
/* Computes pks_hash = tagged_hash(pk[0], ..., pk[np-1]) */
@@ -97,17 +91,11 @@ static int secp256k1_musig_compute_pks_hash(const secp256k1_context *ctx, unsign
/* Initializes SHA256 with fixed midstate. This midstate was computed by applying
* SHA256 to SHA256("KeyAgg coefficient")||SHA256("KeyAgg coefficient"). */
static void secp256k1_musig_keyaggcoef_sha256(secp256k1_sha256 *sha) {
secp256k1_sha256_initialize(sha);
sha->s[0] = 0x6ef02c5aul;
sha->s[1] = 0x06a480deul;
sha->s[2] = 0x1f298665ul;
sha->s[3] = 0x1d1134f2ul;
sha->s[4] = 0x56a0b063ul;
sha->s[5] = 0x52da4147ul;
sha->s[6] = 0xf280d9d4ul;
sha->s[7] = 0x4484be15ul;
sha->bytes = 64;
static const uint32_t midstate[8] = {
0x6ef02c5aul, 0x06a480deul, 0x1f298665ul, 0x1d1134f2ul,
0x56a0b063ul, 0x52da4147ul, 0xf280d9d4ul, 0x4484be15ul
};
secp256k1_sha256_initialize_midstate(sha, 64, midstate);
}
/* Compute KeyAgg coefficient which is constant 1 for the second pubkey and

45
src/modules/musig/session_impl.h
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@@ -309,31 +309,21 @@ static void secp256k1_nonce_function_musig_helper(secp256k1_sha256 *sha, unsigne
/* Initializes SHA256 with fixed midstate. This midstate was computed by applying
* SHA256 to SHA256("MuSig/aux")||SHA256("MuSig/aux"). */
static void secp256k1_nonce_function_musig_sha256_tagged_aux(secp256k1_sha256 *sha) {
secp256k1_sha256_initialize(sha);
sha->s[0] = 0xa19e884bul;
sha->s[1] = 0xf463fe7eul;
sha->s[2] = 0x2f18f9a2ul;
sha->s[3] = 0xbeb0f9fful;
sha->s[4] = 0x0f37e8b0ul;
sha->s[5] = 0x06ebd26ful;
sha->s[6] = 0xe3b243d2ul;
sha->s[7] = 0x522fb150ul;
sha->bytes = 64;
static const uint32_t midstate[8] = {
0xa19e884bul, 0xf463fe7eul, 0x2f18f9a2ul, 0xbeb0f9fful,
0x0f37e8b0ul, 0x06ebd26ful, 0xe3b243d2ul, 0x522fb150ul
};
secp256k1_sha256_initialize_midstate(sha, 64, midstate);
}
/* Initializes SHA256 with fixed midstate. This midstate was computed by applying
* SHA256 to SHA256("MuSig/nonce")||SHA256("MuSig/nonce"). */
static void secp256k1_nonce_function_musig_sha256_tagged(secp256k1_sha256 *sha) {
secp256k1_sha256_initialize(sha);
sha->s[0] = 0x07101b64ul;
sha->s[1] = 0x18003414ul;
sha->s[2] = 0x0391bc43ul;
sha->s[3] = 0x0e6258eeul;
sha->s[4] = 0x29d26b72ul;
sha->s[5] = 0x8343937eul;
sha->s[6] = 0xb7a0a4fbul;
sha->s[7] = 0xff568a30ul;
sha->bytes = 64;
static const uint32_t midstate[8] = {
0x07101b64ul, 0x18003414ul, 0x0391bc43ul, 0x0e6258eeul,
0x29d26b72ul, 0x8343937eul, 0xb7a0a4fbul, 0xff568a30ul
};
secp256k1_sha256_initialize_midstate(sha, 64, midstate);
}
static void secp256k1_nonce_function_musig(secp256k1_scalar *k, const unsigned char *session_secrand, const unsigned char *msg32, const unsigned char *seckey32, const unsigned char *pk33, const unsigned char *agg_pk32, const unsigned char *extra_input32) {
@@ -543,16 +533,11 @@ int secp256k1_musig_nonce_agg(const secp256k1_context* ctx, secp256k1_musig_aggn
/* Initializes SHA256 with fixed midstate. This midstate was computed by applying
* SHA256 to SHA256("MuSig/noncecoef")||SHA256("MuSig/noncecoef"). */
static void secp256k1_musig_compute_noncehash_sha256_tagged(secp256k1_sha256 *sha) {
secp256k1_sha256_initialize(sha);
sha->s[0] = 0x2c7d5a45ul;
sha->s[1] = 0x06bf7e53ul;
sha->s[2] = 0x89be68a6ul;
sha->s[3] = 0x971254c0ul;
sha->s[4] = 0x60ac12d2ul;
sha->s[5] = 0x72846dcdul;
sha->s[6] = 0x6c81212ful;
sha->s[7] = 0xde7a2500ul;
sha->bytes = 64;
static const uint32_t midstate[8] = {
0x2c7d5a45ul, 0x06bf7e53ul, 0x89be68a6ul, 0x971254c0ul,
0x60ac12d2ul, 0x72846dcdul, 0x6c81212ful, 0xde7a2500ul
};
secp256k1_sha256_initialize_midstate(sha, 64, midstate);
}
/* tagged_hash(aggnonce[0], aggnonce[1], agg_pk, msg) */

47
src/modules/schnorrsig/main_impl.h
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@@ -14,33 +14,21 @@
/* Initializes SHA256 with fixed midstate. This midstate was computed by applying
* SHA256 to SHA256("BIP0340/nonce")||SHA256("BIP0340/nonce"). */
static void secp256k1_nonce_function_bip340_sha256_tagged(secp256k1_sha256 *sha) {
secp256k1_sha256_initialize(sha);
sha->s[0] = 0x46615b35ul;
sha->s[1] = 0xf4bfbff7ul;
sha->s[2] = 0x9f8dc671ul;
sha->s[3] = 0x83627ab3ul;
sha->s[4] = 0x60217180ul;
sha->s[5] = 0x57358661ul;
sha->s[6] = 0x21a29e54ul;
sha->s[7] = 0x68b07b4cul;
sha->bytes = 64;
static const uint32_t midstate[8] = {
0x46615b35ul, 0xf4bfbff7ul, 0x9f8dc671ul, 0x83627ab3ul,
0x60217180ul, 0x57358661ul, 0x21a29e54ul, 0x68b07b4cul
};
secp256k1_sha256_initialize_midstate(sha, 64, midstate);
}
/* Initializes SHA256 with fixed midstate. This midstate was computed by applying
* SHA256 to SHA256("BIP0340/aux")||SHA256("BIP0340/aux"). */
static void secp256k1_nonce_function_bip340_sha256_tagged_aux(secp256k1_sha256 *sha) {
secp256k1_sha256_initialize(sha);
sha->s[0] = 0x24dd3219ul;
sha->s[1] = 0x4eba7e70ul;
sha->s[2] = 0xca0fabb9ul;
sha->s[3] = 0x0fa3166dul;
sha->s[4] = 0x3afbe4b1ul;
sha->s[5] = 0x4c44df97ul;
sha->s[6] = 0x4aac2739ul;
sha->s[7] = 0x249e850aul;
sha->bytes = 64;
static const uint32_t midstate[8] = {
0x24dd3219ul, 0x4eba7e70ul, 0xca0fabb9ul, 0x0fa3166dul,
0x3afbe4b1ul, 0x4c44df97ul, 0x4aac2739ul, 0x249e850aul
};
secp256k1_sha256_initialize_midstate(sha, 64, midstate);
}
/* algo argument for nonce_function_bip340 to derive the nonce exactly as stated in BIP-340
@@ -104,16 +92,11 @@ const secp256k1_nonce_function_hardened secp256k1_nonce_function_bip340 = nonce_
/* Initializes SHA256 with fixed midstate. This midstate was computed by applying
* SHA256 to SHA256("BIP0340/challenge")||SHA256("BIP0340/challenge"). */
static void secp256k1_schnorrsig_sha256_tagged(secp256k1_sha256 *sha) {
secp256k1_sha256_initialize(sha);
sha->s[0] = 0x9cecba11ul;
sha->s[1] = 0x23925381ul;
sha->s[2] = 0x11679112ul;
sha->s[3] = 0xd1627e0ful;
sha->s[4] = 0x97c87550ul;
sha->s[5] = 0x003cc765ul;
sha->s[6] = 0x90f61164ul;
sha->s[7] = 0x33e9b66aul;
sha->bytes = 64;
static const uint32_t midstate[8] = {
0x9cecba11ul, 0x23925381ul, 0x11679112ul, 0xd1627e0ful,
0x97c87550ul, 0x003cc765ul, 0x90f61164ul, 0x33e9b66aul
};
secp256k1_sha256_initialize_midstate(sha, 64, midstate);
}
static void secp256k1_schnorrsig_challenge(secp256k1_scalar* e, const unsigned char *r32, const unsigned char *msg, size_t msglen, const unsigned char *pubkey32)