对 msg rsa 签名, 然后使用 base64 encode 编码数据

def rsa_base64_sign_str(self, plain, b64=True):
        """
            对 msg rsa 签名, 然后使用 base64 encode 编码数据

        """
        with open(self.key_file) as fp:
            key_ = RSA.importKey(fp.read())
            # h = SHA.new(plain if sys.version_info < (3, 0) else plain.encode('utf-8'))
            plain = helper.to_bytes(plain)
            # if hasattr(plain, 'encode'):
            #     plain = plain.encode()
            h = SHA.new(plain)
            cipher = pkcs.new(key_).sign(h)
            cip = base64.b64encode(cipher) if b64 else cipher
            return helper.to_str(cip)