sm2签名结果长度不一致

[cqchengdan]

sm2几次签名结果长度不一致问题
代码：
`EC_KEY *ec_key = NULL;
ec_key = EC_KEY_new_by_curve_name(NID_sm2p256v1);
EC_KEY_generate_key(ec_key);

unsigned char buf[20] = {0};
memcpy(buf, "encryption standard", 19);

size_t zlen;
unsigned char z[33] = {0};
SM2_compute_message_digest(EVP_sm3(), EVP_sm3(), buf, sizeof(buf),
                           SM2_DEFAULT_ID_GMT09, SM2_DEFAULT_ID_LENGTH, z, &zlen, ec_key);
for(int i=0; i<zlen; i++)
    printf("%02x", z[i]);
printf("\n");
cout << "zlen=" << zlen << endl;

unsigned int signlen;
//SM2_sign(NID_sm3, z, zlen, NULL, &signlen, ec_key);
//cout << "signlen=" << signlen << endl;
//unsigned char *signMsg = new unsigned char[signlen+1];
//memset(signMsg, 0, signlen+1);

unsigned char signMsg[SM2_MAX_SIGNATURE_LENGTH] = {0};
SM2_sign(NID_sm3, z, zlen, signMsg, &signlen, ec_key);
cout << "signlen=" << signlen << endl;
for(int i=0; i<signlen; i++)
    printf("%02x", signMsg[i]);
printf("\n");

EC_KEY_free(ec_key);`

两次执行结果，一次长度71，一次70
[root@localhost Desktop]# ./sig
2e6c09837e3eab76ac9c61bd6a8a3053caf3c3f80dc3fbb4abbe4ce65dcd0cff
zlen=32
signlen=71
304502205c4e47e7c240c2bc71d42ee5d9f59002f36b51b233d2f35884c31edff6bc4a06022100e3d8c43fe32677697938c953040aa7f874cfe0dbad18a50e53f9f3bd18fdd7f8
[root@localhost Desktop]# ./sig
0329b63f13e9fe1f94876d7f7fd399d79750979eee16a07196de8a06d21b37f1
zlen=32
signlen=70
304402204105aaf3b0a9d6dfe817cca6f15f5d408ecb3d1626107a553f8775556d3b649402203bcec2d239c90b03b8536f2d3f037ac3de7cef6bfc8b18fa815f625c70357584

[wumingyuan]

刚做完这个，你需要的是R||S模式，要在上述基础上做转换：
`
sig = d2i_ECDSA_SIG(NULL, &p, sig_len);
if (sig)
{
ECDSA_SIG_get0(sig, &sig_r, &sig_s);
sig_len = BN_bn2bin(sig_r, sig_bin);
sig_len += BN_bn2bin(sig_s, sig_bin + sig_len);

ECDSA_SIG_free(sig);

}
`
上述p和sig_len分别为sm2_sign返回的签名和长度

[strongbug]

SM2签名值做了der编码，格式是
SM2Signature :== SEQUENCE{
INTEGER r,
INTEGER s,
}
在大数INTEGER做der编码时，如果首字节的第一个二进制位为1时，前面需要补00字节，所以导致der编码长度为多一个字节，这种情况下SM2签名值得编码长度最大会有两个字节的差距。

[github-actions]

Marked as stale issue. Will be closed later if no activity for a while.