RSA_padding_add_PKCS1_type_1返回一个空值

Question

我想添加块类型01填充来签名哈希

当我使用RSA_padding_add_PKCS1_type_1函数时，它在缓冲区变量中返回空值

这是我的代码

    size_t buflen = EVP_PKEY_size(pkey)/8;
    unsigned char * buffer = (unsigned char *)OPENSSL_malloc(buflen);
    RSA_padding_add_PKCS1_type_1(buffer, buflen, digestmsg,digestLen );