Decrypt/verify file

        :param encrypted_file: File-like object containing encrypted data
        :param passphrase: Passphrase
        :param signer_key: Signer key ID. Sign will not be verifyed when None
        :param always_trust: Skip key validation and assume that used keys are always fully trusted
        :param output_filename: Decrypted data will be written to this file when not None
        :rtype: EncryptResult

def decrypt_file(self, encrypted_file, passphrase, signer_key=None,
                     always_trust=False, output_filename=None):
        '''
        Decrypt/verify file

        :param encrypted_file: File-like object containing encrypted data
        :param passphrase: Passphrase
        :param signer_key: Signer key ID. Sign will not be verifyed when None
        :param always_trust: Skip key validation and assume that used keys are always fully trusted
        :param output_filename: Decrypted data will be written to this file when not None
        :rtype: EncryptResult
        '''
        args = ['--decrypt']
        if signer_key:
            args += ('-u', signer_key)
        if output_filename:
            if os.path.exists(output_filename):
                # to avoid overwrite confirmation message
                os.remove(output_filename)
            args += ('--output', output_filename)
        if always_trust:
            #args.append ('--always-trust')
            args += ('--trust-model', 'always')
        return self.execute(DecryptResult(), args, passphrase, encrypted_file, True)