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FAQ: Find duplicate files, compare and checksum files

Topics: find duplicate files, deduplicate files, detect corrupted files, calculate checksum program, calculate hash, cryptographically secure hash functions, compare files software, freeware duplicate finder application, find duplicates.

How to find duplicate files using checksum, hash and file compare?

PeaZip can be used as duplicate files finder, or to spot differences between two files, using its "File tools" features:

Calculate checksum and hash
PeaZip's "Check files" tool in "File tools" submenu can perform multiple, user selected hash find duplicate hash

and checksum file compare

algorithms on multiple files at once.

This function supports many algorithms ranging from fast checksums to cryptographically strong hashes: Adler32, CRC family (CRC16, CRC24, CRC32, CRC64), eDonkey/eMule, MD4, MD5, Ripemd160, SHA families (SHA1; SHA224, SHA256, SHA384, SHA512), and Whirlpool512.
The algorithms to be performed can be selected in Options > Settings, in File Tools tab.

Hint: Chose faster checksums like CRC32 to perform a quick comparation to detect duplicate files of test for casual corruption, but it is recommended to switch to a cryptographically secure hash function (like SHA 256, SHA512 or the AES-based Whirlpool512) to detect malicious corruption attempt that might be calculated in order to pass undetected to one (or some) of the non-secure algorithms.

Selected algorithms are performed in a single passage so reading the disk (usually the main performance bottleneck) occours only one time.
Calculating file hash or checksum is useful in example to find duplicate files and to check files for corruption when an original checksum or hash value is known.
Output value of hashes and checksums can be seen as exadecimal (HEX, either LSB or MSB) or encoded as Base64.

Byte to byte file comparison
"Compare files" tools in "File tools" submenu, instead, performs byte to byte comparison between two files.
Unlike checksum or hash based comparison, byte to byte comparison can spot exactly what are the different bytes and it is not susceptible of collisions under any circumstance - even if this condition is highly ulikely if the chosen algorithm is adequately strong for the scenario where it is intended to be used.

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