EVP_PKT_SIGN
ret = EVP_PK_RSA | EVP_PKT_SIGN;
ret = EVP_PK_RSA | EVP_PKT_SIGN;
ret = EVP_PK_DSA | EVP_PKT_SIGN;
ret = EVP_PK_EC | EVP_PKT_SIGN | EVP_PKT_EXCH;
ret = EVP_PKT_SIGN;
ret = EVP_PKT_EXCH | EVP_PKT_SIGN;