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perf: optimize pubkey generation by removing unnecessary constant-tim… #793

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25 changes: 17 additions & 8 deletions secp256k1-sys/depend/secp256k1/src/secp256k1.c
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Original file line number Diff line number Diff line change
Expand Up @@ -544,30 +544,39 @@ int rustsecp256k1_v0_11_ec_seckey_verify(const rustsecp256k1_v0_11_context* ctx,

static int rustsecp256k1_v0_11_ec_pubkey_create_helper(const rustsecp256k1_v0_11_ecmult_gen_context *ecmult_gen_ctx, rustsecp256k1_v0_11_scalar *seckey_scalar, rustsecp256k1_v0_11_ge *p, const unsigned char *seckey) {
rustsecp256k1_v0_11_gej pj;
int ret;

ret = rustsecp256k1_v0_11_scalar_set_b32_seckey(seckey_scalar, seckey);
rustsecp256k1_v0_11_scalar_cmov(seckey_scalar, &rustsecp256k1_v0_11_scalar_one, !ret);
int overflow;

/* Fast path: directly set scalar from bytes without constant-time ops */
rustsecp256k1_v0_11_scalar_set_b32(seckey_scalar, seckey, &overflow);
if (overflow || rustsecp256k1_v0_11_scalar_is_zero(seckey_scalar)) {
return 0;
}

/* Public key generation doesn't need constant time ops */
rustsecp256k1_v0_11_ecmult_gen(ecmult_gen_ctx, &pj, seckey_scalar);
rustsecp256k1_v0_11_ge_set_gej(p, &pj);

/* Convert jacobian to affine coordinates directly */
rustsecp256k1_v0_11_ge_set_gej_var(p, &pj);
rustsecp256k1_v0_11_gej_clear(&pj);
return ret;

return 1;
}

int rustsecp256k1_v0_11_ec_pubkey_create(const rustsecp256k1_v0_11_context* ctx, rustsecp256k1_v0_11_pubkey *pubkey, const unsigned char *seckey) {
rustsecp256k1_v0_11_ge p;
rustsecp256k1_v0_11_scalar seckey_scalar;
int ret = 0;

VERIFY_CHECK(ctx != NULL);
ARG_CHECK(pubkey != NULL);
memset(pubkey, 0, sizeof(*pubkey));
ARG_CHECK(rustsecp256k1_v0_11_ecmult_gen_context_is_built(&ctx->ecmult_gen_ctx));
ARG_CHECK(seckey != NULL);

ret = rustsecp256k1_v0_11_ec_pubkey_create_helper(&ctx->ecmult_gen_ctx, &seckey_scalar, &p, seckey);
rustsecp256k1_v0_11_pubkey_save(pubkey, &p);
rustsecp256k1_v0_11_memczero(pubkey, sizeof(*pubkey), !ret);
if (ret) {
rustsecp256k1_v0_11_pubkey_save(pubkey, &p);
}

rustsecp256k1_v0_11_scalar_clear(&seckey_scalar);
return ret;
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