openssl - 调用函数 EVP_DigestSignFinal 时出错

Question

我正在尝试使用客户引擎实现 ECDSA，但在 EVP_DigestSignFinal(mdctx, sig, slen)) 这一行遇到错误。谁能指导我。

引擎部分-->

EVP_PKEY_meth_set_sign(dasync_ec, dasync_ec_signinit,
           dasync_ec_sign);

static int dasync_ec_sign(EVP_PKEY_CTX *ctx, unsigned char *sig, size_t *siglen, const unsigned char *tbs, size_t tbslen)
{
    static int (*psign)(EVP_PKEY_CTX *ctx, unsigned char *sig, size_t *siglen, const unsigned char *tbs, size_t tbslen);
    if (psign == NULL)
        EVP_PKEY_meth_get_sign(dasync_ec_orig, NULL, &psign);    
    return psign(ctx,sig,siglen,tbs,tbslen);
}

测试端-->

 EVP_MD_CTX *mdctx=NULL;
 EVP_PKEY *pkey =  EVP_PKEY_new(); 
 EC_KEY *eckey=NULL;
 eckey=EC_KEY_new();
 size_t *slen;
 EVP_PKEY_assign_EC_KEY(pkey,eckey);

if(!(mdctx = EVP_MD_CTX_create())) 
   goto err;
if(1 != EVP_DigestSignInit(mdctx, NULL, EVP_sha256(), my_engine, pkey)) 
   goto err; 
if(1 != EVP_DigestSignUpdate(mdctx, msg, strlen(msg))) 
   goto err;
if(1 != EVP_DigestSignFinal(mdctx, NULL, slen)) 
   goto err;
if(!(*sig = OPENSSL_malloc(sizeof(unsigned char) * (*slen)))) 
   goto err;
if(1 != EVP_DigestSignFinal(mdctx, sig, slen)) 
 goto err;