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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 footer_length(header):
 """Calculates the ciphertext message footer length, given a complete header. :param header: Complete message header object :type header: aws_encryption_sdk.structures.MessageHeader :rtype: int """

    footer_length = 0
    if header.algorithm.signing_algorithm_info is not None:
        footer_length += 2  # Signature Length
        footer_length += header.algorithm.signature_len  # Signature
    return footer_length