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PeaZip, free archiver utility, Open Source WinRar / WinZip alternative for Windows and Linux.
Compress to 7Z, ARC, BZ2, GZip, PAQ, PEA, self-extracting archives, TAR, WIM, XZ, ZIP files.
Open 150+ file types, including ACE, CAB, DMG, ISO, RAR, UDF, ZIPX format.
Extract, create and convert archives, split / join files, strong encryption, encrypted password manager, secure delete, find duplicate files, compute hash, export job definition as script to automate backup / restore.

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compute checksum hash algorithm

Find duplicate files, hash, checksum


How to detect identical files, calculate checksum and hash


How to detect identical files, calculate checksum and hash


PeaZip can be used as duplicate files finder, searching binary identical files in order to de-duplicate data for saving disk space occupation, or improving compression through elimination of redundancy of input information, using various detection methods:

Find duplicate files in the file manager


When browsing a filesystem (not inside a compressed archive) the file browser can show file checksum / hash value on demand in last column, allowing to identify binary identical files which have same checksum/hash value.
Clicking the name of the function (in context menu, "File tools" group) will display hash or checksum value for all (or selected) files.
Clicking "Find duplicates" will display size and hash or checksum value only for duplicate files - same binary identical content featured in two or more distinct files - and report the number of non-unique files identified.
In both cases, sorting for CRC column allows to group all files (in same folder, or same search filter) with identical hash or checksum.
The verification function can be set in main application's menu: Organize, Browser, Checksum/hash), a wide selection of algorithms can be selected, ranging from simple checksum functions as Adler32, CRC family (CRC16, CRC24, CRC32, and CRC64) to hash functions like eDonkey/eMule, MD4, MD5, and cryptographically strong hash as Ripemd160, SHA-1 and SHA-2 (SHA224, SHA256, SHA384, SHA512), and Whirlpool512.

indentify redundant data

When browsing an archive this on demand verification is not available, but (if supported by the archive format) the CRC column will display data integrity information, i.e. CRC32 in ZIP archives, allowing to sort archive content by CRC column to group identical files and find out duplicates.


Identify similar images in the file manager


When browsing a filesystem, PeaZip can display thumbnails of graphic files: context menu, organize, check show picture thumbnails, or select a file browser's preset style showing thumbnails.
While checksum/hash based inspection allows to find exactly identical files (and images), thumbnails allows the user to find similar images (i.e. same picture or graphic saved in different formats, or with different color depth or compression settings, or scaled to different sizes), to help in deciding if the (pseudo)duplication is acceptable, and what copy to keep.


Calculate multiple checksum and hash functions at once


Check files utility in "File tools" submenu (context menu) allows to verify multiple hash and checksum algorithms (same pool of algorithms supported in the file manager for data deduplication) on multiple files at once, e.g. to compare a group of file to identify redundant ones, or to check files for corruption when an original checksum or hash value is known.
Selected algorithms are performed in a single passage so reading the data from disk (usually the main performance bottleneck) occurs only one time, speeding up the disk-bound part of the process

The algorithms to be performed can be selected in Options > Settings, in File Tools tab; output value of hashes and checksums can be seen as exadecimal (HEX, either LSB or MSB) or encoded as Base64.

Hint: chose faster checksums like CRC32 to perform a quick comparison (e.g. to detect duplicate files of test for casual corruption data errors), but it is recommended to employ a cryptographically secure hash function (like SHA256, SHA512 or the AES-based Whirlpool512) to detect malicious corruption / forgery attacks that might be calculated in order to pass undetected to one (or some) of the non-secure algorithms exploiting collision - algorithm maps different input to same ouput digest.

Use of multiple functions, and especially relying on cryptographically strong hash functions as Ripemd, SHA-2 or Whirlpool, can defeat attempt of forging identical-looking files, as it is computationally feasible to find a collision (different input mapped to same output) for simpler checksum and hash functions.
This way, even a purposely crafted modification of a file would not pass unnoticed to most sophisticated detection algorithms.


Alternative: byte-to-byte comparison

Compare files utility in "File tools" submenu performs byte to byte comparison between two files; unlike checksum/hash method it is not subject of collisions under any circumstance, and can report what the different bytes are - so it not only tells if two files are not identical, but also what changes were made between the two versions.

Topics: how to find duplicate files on Microsoft Windows and Linux systems, compare and deduplicate content, detect redundant data, remove identical files, calculate checksum algorithm, compute hash value, identify similar images.

Related articles: How to improve file compression performances, How to encrypt archives, Extract encrypted archives, Protect files, Secure delete, Split and join files

FAQ > File management > Find file hash, calculate checksum, deduplicate data





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