Decrypts encrypted data message
        @param key - symmetic key to decrypt
        @param flags - OR-ed combination of Flags constant

def decrypt(self, key, flags=0):
        """
        Decrypts encrypted data message
        @param key - symmetic key to decrypt
        @param flags - OR-ed combination of Flags constant
        """
        bio = Membio()
        if libcrypto.CMS_EncryptedData_decrypt(self.ptr, key, len(key), None,
                                               bio.bio, flags) <= 0:
            raise CMSError("decrypt data")
        return str(bio)