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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) {