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Introduce hash context to support pluggable SHA256 compression

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This is purely a mechanical change with no behavior change.

It introduces a secp256k1_hash_ctx struct inside secp256k1_context
and propagates it to all SHA256-related operations.

This sets up the ability to provide a hardware-optimized SHA256
compression function at runtime in a follow-up commit.
This commit is contained in:
furszy
2025-12-17 11:15:33 -05:00
parent 95e6815843
commit fdb6a91a5e
21 changed files with 313 additions and 238 deletions
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12
src/ecmult_gen_impl.h
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@@ -14,8 +14,8 @@
#include "hash_impl.h"
#include "precomputed_ecmult_gen.h"
static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context *ctx) {
secp256k1_ecmult_gen_blind(ctx, NULL);
static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context *ctx, const secp256k1_hash_ctx *hash_ctx) {
secp256k1_ecmult_gen_blind(ctx, hash_ctx, NULL);
ctx->built = 1;
}
@@ -282,7 +282,7 @@ static void secp256k1_ecmult_gen(const secp256k1_ecmult_gen_context *ctx, secp25
}
/* Setup blinding values for secp256k1_ecmult_gen. */
static void secp256k1_ecmult_gen_blind(secp256k1_ecmult_gen_context *ctx, const unsigned char *seed32) {
static void secp256k1_ecmult_gen_blind(secp256k1_ecmult_gen_context *ctx, const secp256k1_hash_ctx *hash_ctx, const unsigned char *seed32) {
secp256k1_scalar b;
secp256k1_scalar diff;
secp256k1_gej gb;
@@ -309,17 +309,17 @@ static void secp256k1_ecmult_gen_blind(secp256k1_ecmult_gen_context *ctx, const
*/
VERIFY_CHECK(seed32 != NULL);
memcpy(keydata + 32, seed32, 32);
secp256k1_rfc6979_hmac_sha256_initialize(&rng, keydata, 64);
secp256k1_rfc6979_hmac_sha256_initialize(hash_ctx, &rng, keydata, 64);
secp256k1_memclear_explicit(keydata, sizeof(keydata));
/* Compute projective blinding factor (cannot be 0). */
secp256k1_rfc6979_hmac_sha256_generate(&rng, nonce32, 32);
secp256k1_rfc6979_hmac_sha256_generate(hash_ctx, &rng, nonce32, 32);
secp256k1_fe_set_b32_mod(&f, nonce32);
secp256k1_fe_cmov(&f, &secp256k1_fe_one, secp256k1_fe_normalizes_to_zero(&f));
ctx->proj_blind = f;
/* For a random blinding value b, set scalar_offset=diff-b, ge_offset=bG */
secp256k1_rfc6979_hmac_sha256_generate(&rng, nonce32, 32);
secp256k1_rfc6979_hmac_sha256_generate(hash_ctx, &rng, nonce32, 32);
secp256k1_scalar_set_b32(&b, nonce32, NULL);
/* The blinding value cannot be zero, as that would mean ge_offset = infinity,
* which secp256k1_gej_add_ge cannot handle. */