EVP_DigestSignUpdate(mac_ctx, header, sizeof(header));
EVP_DigestSignUpdate(mac_ctx, rec->input, rec->length);
t = EVP_DigestSignFinal(mac_ctx, md, &md_size);
EVP_DigestSignUpdate(mac_ctx, header, sizeof(header));
EVP_DigestSignUpdate(mac_ctx, rec->input, rec->length);
t = EVP_DigestSignFinal(mac_ctx, md, &md_size);