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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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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)