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FAQ / SUPPORTED FILE FORMATS > 7Z FILES
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Verify file integrity (hash, checksum)



COMPUTE CRC, MD5, SHA, RIPEMD HASH TO DETECT DATA CORRUPTION

MORE INFORMATION ABOUT INTEGRITY CHECKING

detect file corruption



PeaZip provides primitives to compute multiple hash and checksum algorithms, and this feature can be used either to find duplicate files (which have identical checksum/hash value), and to detect corrupted files which have different checksum/hash value from a known one.


Compute error detection algorithms


Check files entry 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; output value of hashes and checksums can be seen as exadecimal (HEX, either LSB or MSB) or encoded as Base64.

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)

    • AES-based Whirlpool512


error detection algorithm

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 sha-2-family SHA256, SHA512, 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.

calculate file hash


Using multiple functions at once, and especially relying on cryptographically strong hash functions as Ripemd160, 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, 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 entry in "File tools" submenu performs byte to byte comparison between two files, a slower process in which all single bytes of one file are matched with the same offset byte of the other one.
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 for errors


Most archive formats can be tested for errors using PeaZip 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.
Some archive types (7z, rar, tar, zipx...) improves error detection storing pre-computed checksum values (usually CRC32) 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, Ripemd, Whirlpool) against a known value, using aforementioned "Check files" tool.
PEA file format provides a wide array of strong hash functions and authenticated encryption options so the archive integrity can be thoroughly tested during extraction.

More information about integrity checking


External online resources: 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.

Topics and serach suggestions: how to detect corrupted or forged files, verify hash value, identify data corruption computing checksum and hash functions, FIPS, CRC32, Adler, MD5, SHA, SHA2 algorithms, file integrity checker tool, compute cryptographic hash function, software detecting modified data, test file for data errors.


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