The particular message digest will change if the file changes. Not only can message digests help determine file changes, but can also assist in locating duplicate files.
Message digests can be produced on UNIX systems with the MD5 command. MD5s are securely stored on systems and can reveal if an unauthorized user has accessed a file. It has been shown that MD5 is unreliable with problems relating to collision (where 2 keys for different data are the same) and it is no longer used.
File sharing programs, such as peer-to-peer (P2P), utilize message digests to warn users when downloading identical files. It can also pinpoint the origin of duplicate downloads. Besides MD5, SHA and CRC32 are other message digest algorithms.
Message digests are encrypted with private keys creating a digital signature. This results in a type of validation ensuring that the appropriate user is accessing protected information. Message digests protect one-way hash algorithms taking random data and transmitting a set length hash value.
To begin the process a message digest is initialized. Then the data is processed through the message digest by using updates. Final operations include padding, during which the message digest completes the hash computation and resets itself. However, the digest can be reset at any time during the process.
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