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File Checksums

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Duplicate File Detective can compare the contents of files by computing the file's content checksum. This checksum is a numerical representation of the file's contents derived through a series of mathematical computations - a process known as hashing.


Duplicate File Detective offers a range of hashing algorithms:


CRC32 - Quick checksum (32 bits)

ADLER32 - Quick checksum (32 bits)

MD5 - Medium strength, slower checksum (128 bits)

SHA1 - Stronger, slower checksum (160 bits)

SHA256 - Even stronger, slower checksum (256 bits)

SHA512 - Even stronger, slower checksum (512 bits)


Generally speaking, the "stronger" the checksum / hashing method, the more likely it is that two files compared with the resulting checksum will be identical. Stronger hashing algorithms are also generally a bit slower than weaker ones.


Note that file content hashing algorithms such as MD5 and SHA are extremely unlikely to produce false positives (e.g. mistakenly identify two files as being identical to one another when they actually different). Even the smallest differences in file contents will (with overwhelming probability) result in completely different hashes due to a cryptographic concept known as the avalanche effect. If you must be absolutely certain that two files are identical, use the byte-for-byte content match confirmation option.


Tip: Duplicate File Detective provides a File Hash Calculator feature that you can use to experiment with the computation of file checksums.



See also:

File Matching