md6 message digest algorithm 6 with sizes up to 512 bits and sha n secure hash algorithm u2018 n u2019 with sizes up to 1024 bits the message digest is used as part of the validation to see if a particular file should be streamed to the client a practical issue is hash collision where two different files produce the same hash value sha 2 has no known hash collisions and is the default in a preferred embodiment to further reduce the risk of a hash collision possibly affecting the update caches the size of the file m_filesize and the time stamp of the most recent file change m_lastchangetime are also used in the comparing against the update cache all supported message digests algorithms are predefined as integers and the one used encoded in the field u2018 m_messagedigestalgorithm u201d another field u201c m_compressionon u201d determines if compression is used for the particular file corresponding to the cacheline depending on file size network bandwidth and available cpu cycles files may selectively be compressed prior to being streamed to the client all supported compression algorithms are pre defined as integers and the one used encoded in the field u201c m_compressionalgorithm u201d compression algorithms are provided as part.