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File hashing utility, verify CRC MD5 SHA256 hash values

Open Source file hash utility, compute CRC, MD5, SHA256 tool
Calculate hash, checksum to detect data corruption and forgery






PeaZip is a free, Open Source file hashing utility which provides primitives to compute multiple hash and checksum algorithms.
File hash computation can be used either to find duplicate files (which have identical checksum/hash value), and to detect corrupted files which have different checksum / hash values from a known one.

Why it is needed to verify data integrity

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Data corruption may arise by simple technical issues - transmission faults, degradation of memory support - which can usually be detected with ease by quick and computationally light functions (often integrated at various levels of transmission protocols and memory technologies), or may arise from forgery, purposely crafted modifications of data created by a malicious attacker to exploit weakness of simpler error detection mechanisms - which requires calculation of more powerful verification functions like cryptographically strong hash algorithms.

Compute error detection algorithms

Check files tool in "File tools" submenu (context menu) allows to verify multiple hash and checksum algorithms 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 (or when it can be calculated for reference from a known safe copy of the data).
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; calculated output value of hashes and checksums can be seen as exadecimal (HEX, either LSB or MSB) or encoded as Base64.

CRC and hashing algorithms supported by PeaZip

15 checksum and hash algorithms are currently supported:
  • checksum functions Adler32, CRC16, CRC24, CRC32, CRC64

  • general-purpose hash functions as eDonkey/eMule, MD4, MD5

  • cryptographically strong hash:

    • Ripemd160

    • SHA-1

    • SHA-2 family (SHA256, SHA512)

    • SHA-3 family (SHA-3 256, SHA-3 512)

    • BLAKE2S and BLAKE2B
    • AES-based Whirlpool512

File hash verification best practices

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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 BLAKE2S or BLAKE2B, SHA256, SHA-3 algorithms, 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.

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Use multiple hash functions at once
Employing multiple functions at once, and especially relying on cryptographically strong hash functions as Ripemd160, SHA-2, SHA-3 or Whirlpool, can defeat attempt of forging identical-looking files, as it is computationally feasible to find a collision (different input files mapped to same output digest) for simpler checksum and hash functions, while finding digest value collisions is currently not computationally feasible for more robust cryptographic hash functions.

This way, even a purposely crafted modification of a file would not pass unnoticed to most sophisticated error / forgery detection algorithms, making possible to identify not only plain data corruption (e.g. communication or device fault) but also to avoid certain classes of attacks relying on replacing original content with forged data.

Byte-to-byte file comparison

Compare files tool in "File tools" submenu performs byte to byte comparison between two files, a slower process in which all single bytes of one file are verified and matched with the same offset byte of the other file.
Unlike checksum / hash comparison, this method it is not subject to collisions under any circumstance, and can effectively tell what the different bytes are, providing not only a way to verify if two files are identical or different, but also to find in details what changes were made between the two versions.

Test archive files for errors

Most archive formats can be tested for errors using PeaZip Open Source file hash utility routines (Test button), detecting if data is correctly readable and matches file format specification's standards, either testing archive table of content and single archive items.

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Some archive types (7z, rar, tar, zipx...) improves error detection storing pre-computed checksum values (usually CRC32, RAR format can optionally use 256-bit BLAKE2sp hash) of archived data.
Data errors can be due to random corruption (faulty support, troubles during download), out of standard archiving processes (bug, obsolete specifications), or in worst case purposeful alteration of original content. In some cases corruption or alteration of data can lead to an unreadable archive as result.
Testing archives for errors is an useful good practice sufficient for low risk scenarios, but if there is a reasonable suspicion of the data being purposely manipulated it is preferable to test the file with a cryptographically strong hash function (SHA family, Ripemd, Whirlpool) against a known value, using aforementioned "Check files" tool.

Integrity checking in PEA archives

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PEA file format provides a wide array of strong hash functions and authenticated encryption options, saving inside the archive the calculated digest values - Adler, CRC32, CRC64, MD5, SHA1, Ripemd, SHA2 (SHA256, SHA512) and SHA3 (SHA-3 256, SHA-3 512), Whirlpool, plus OMAC or HMAC for authenticated encryption (default EAX AES256 CTR+OMAC).
In this way the data integrity can be thoroughly tested during extraction, reducing needs of relying on external file hashing tools, for verification both of integrity and autenticity of the content.

Read more about error detection and related topics: definitions of data integrityverify file content, checksumvalidate data integrity, hashfind hash value, cryptographically secure hash functioncryptographic hash algorithms, and data deduplicationidentify duplicates on Wikipedia, sha-2-familyfips certified hash standard.

Synopsis: Error detection, how to verify data integrity with PeaZip, freeware Open Source file hashing utility. Calculate CRC checksum and MD5, SHA256 file hash values to detect corrupt files.

Topics: how to compute crc, verify md5, sha256 hash values, detect corrputed files, test files for data errors

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