+int sm2_compute_z_digest(uint8_t *out,
+ const EVP_MD *digest,
+ const uint8_t *id,
+ const size_t id_len,
+ const EC_KEY *key)
+{
+ int rc = 0;
+ const EC_GROUP *group = EC_KEY_get0_group(key);
+ BN_CTX *ctx = NULL;
+ EVP_MD_CTX *hash = NULL;
+ BIGNUM *p = NULL;
+ BIGNUM *a = NULL;
+ BIGNUM *b = NULL;
+ BIGNUM *xG = NULL;
+ BIGNUM *yG = NULL;
+ BIGNUM *xA = NULL;
+ BIGNUM *yA = NULL;
+ int p_bytes = 0;
+ uint8_t *buf = NULL;
+ uint16_t entl = 0;
+ uint8_t e_byte = 0;
+
+ hash = EVP_MD_CTX_new();
+ ctx = BN_CTX_new();
+ if (hash == NULL || ctx == NULL) {
+ SM2err(SM2_F_SM2_COMPUTE_Z_DIGEST, ERR_R_MALLOC_FAILURE);
+ goto done;
+ }
+
+ p = BN_CTX_get(ctx);
+ a = BN_CTX_get(ctx);
+ b = BN_CTX_get(ctx);
+ xG = BN_CTX_get(ctx);
+ yG = BN_CTX_get(ctx);
+ xA = BN_CTX_get(ctx);
+ yA = BN_CTX_get(ctx);
+
+ if (yA == NULL) {
+ SM2err(SM2_F_SM2_COMPUTE_Z_DIGEST, ERR_R_MALLOC_FAILURE);
+ goto done;
+ }
+
+ if (!EVP_DigestInit(hash, digest)) {
+ SM2err(SM2_F_SM2_COMPUTE_Z_DIGEST, ERR_R_EVP_LIB);
+ goto done;
+ }
+
+ /* Z = h(ENTL || ID || a || b || xG || yG || xA || yA) */
+
+ if (id_len >= (UINT16_MAX / 8)) {
+ /* too large */
+ SM2err(SM2_F_SM2_COMPUTE_Z_DIGEST, SM2_R_ID_TOO_LARGE);
+ goto done;
+ }
+
+ entl = (uint16_t)(8 * id_len);
+
+ e_byte = entl >> 8;
+ if (!EVP_DigestUpdate(hash, &e_byte, 1)) {
+ SM2err(SM2_F_SM2_COMPUTE_Z_DIGEST, ERR_R_EVP_LIB);
+ goto done;
+ }
+ e_byte = entl & 0xFF;
+ if (!EVP_DigestUpdate(hash, &e_byte, 1)) {
+ SM2err(SM2_F_SM2_COMPUTE_Z_DIGEST, ERR_R_EVP_LIB);
+ goto done;
+ }
+
+ if (id_len > 0 && !EVP_DigestUpdate(hash, id, id_len)) {
+ SM2err(SM2_F_SM2_COMPUTE_Z_DIGEST, ERR_R_EVP_LIB);
+ goto done;
+ }
+
+ if (!EC_GROUP_get_curve(group, p, a, b, ctx)) {
+ SM2err(SM2_F_SM2_COMPUTE_Z_DIGEST, ERR_R_EC_LIB);
+ goto done;
+ }
+
+ p_bytes = BN_num_bytes(p);
+ buf = OPENSSL_zalloc(p_bytes);
+ if (buf == NULL) {
+ SM2err(SM2_F_SM2_COMPUTE_Z_DIGEST, ERR_R_MALLOC_FAILURE);
+ goto done;
+ }
+
+ if (BN_bn2binpad(a, buf, p_bytes) < 0
+ || !EVP_DigestUpdate(hash, buf, p_bytes)
+ || BN_bn2binpad(b, buf, p_bytes) < 0
+ || !EVP_DigestUpdate(hash, buf, p_bytes)
+ || !EC_POINT_get_affine_coordinates(group,
+ EC_GROUP_get0_generator(group),
+ xG, yG, ctx)
+ || BN_bn2binpad(xG, buf, p_bytes) < 0
+ || !EVP_DigestUpdate(hash, buf, p_bytes)
+ || BN_bn2binpad(yG, buf, p_bytes) < 0
+ || !EVP_DigestUpdate(hash, buf, p_bytes)
+ || !EC_POINT_get_affine_coordinates(group,
+ EC_KEY_get0_public_key(key),
+ xA, yA, ctx)
+ || BN_bn2binpad(xA, buf, p_bytes) < 0
+ || !EVP_DigestUpdate(hash, buf, p_bytes)
+ || BN_bn2binpad(yA, buf, p_bytes) < 0
+ || !EVP_DigestUpdate(hash, buf, p_bytes)
+ || !EVP_DigestFinal(hash, out, NULL)) {
+ SM2err(SM2_F_SM2_COMPUTE_Z_DIGEST, ERR_R_INTERNAL_ERROR);
+ goto done;
+ }
+
+ rc = 1;
+
+ done:
+ OPENSSL_free(buf);
+ BN_CTX_free(ctx);
+ EVP_MD_CTX_free(hash);
+ return rc;
+}
+