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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def deserialize_tag(stream, header, verifier=None):
 """Deserialize the Tag value from a non-framed stream. :param stream: Source data stream :type stream: io.BytesIO :param header: Deserialized header :type header: aws_encryption_sdk.structures.MessageHeader :param verifier: Signature verifier object (optional) :type verifier: aws_encryption_sdk.internal.crypto.Verifier :returns: Tag value for body :rtype: bytes """

    (data_tag,) = unpack_values(
        format_string=">{auth_len}s".format(auth_len=header.algorithm.auth_len), stream=stream, verifier=verifier
    )
    return data_tag