Simple file verification (SFV) is a file format for storing CRC32checksums of files to verify the integrity of files. SFV is used to verify that a file has not been corrupted, but it does not otherwise verify the file's authenticity. The .sfvfile extension is usually used for SFV files.[1]
Files can become corrupted for a variety of reasons, including faulty storage media, errors in transmission, write errors during copying or moving, and software bugs. SFV verification ensures that a file has not been corrupted by comparing the file's CRChash value to a previously calculated value.[1] Due to the nature of hash functions, hash collisions may result in false positives, but the likelihood of collisions is usually negligible with random corruption. (The number of possible checksums is limited though large, so that with any checksum scheme many files will have the same checksum. However, the probability of a corrupted file having the same checksum as its original is exceedingly small, unless deliberately constructed to maintain the checksum.)
SFV cannot be used to verify the authenticity of files, as CRC32 is not a collision resistant hash function; even if the hash sum file is not tampered with, it is computationally trivial for an attacker to cause deliberate hash collisions, meaning that a malicious change in the file is not detected by a hash comparison. In cryptography, this attack is called a collision attack. For this reason, the md5sum and sha1sum utilities are often preferred in Unix operating systems, which use the MD5 and SHA-1cryptographic hash functions respectively.
Even a single-bit error causes both SFV's CRC and md5sum's cryptographic hash to fail, requiring the entire file to be re-fetched. The Parchive and rsync utilities are often preferred for verifying that a file has not been accidentally corrupted in transmission, since they can correct common small errors with a much shorter download.
Despite the weaknesses of the SFV format, it is popular due to the relatively small amount of time taken by SFV utilities to calculate the CRC32 checksums when compared to the time taken to calculate cryptographic hashes such as MD5 or SHA-1.
SFV uses a plain text file containing one line for each file and its checksum[1] in the format FILENAME<whitespaces>CHECKSUM. Any line starting with a semicolon ';' is considered to be a comment and is ignored for the purposes of file verification. The delimiter between the filename and checksum is always one or several spaces; tabs are never used. A sample SFV file is:
; This is a comment file_one.zip c45ad668 file_two.zip 7903b8e6 file_three.zip e99a65fb
Total Commander - supports creation and verification of SFV files
hkSFV - supports creation and verification of SFV files (crashes on massive SFV files check)
DySFV - Open Source (free) application for large files
ilSFV - free and open-source SFV, MD5 and SHA-1 file verification utility.
December 18, 2023
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This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Simple file verification news newspapers books scholar JSTOR September 2018 Learn how and when to remove this template message This article may require cleanup to meet Wikipedia s quality standards The specific problem is Needs refocussing on sfv extension rather than overlapping with File verification Relevant discussion may be found on Talk File verification Please help improve this article if you can November 2022 Learn how and when to remove this template message Simple file verification SFV is a file format for storing CRC32 checksums of files to verify the integrity of files SFV is used to verify that a file has not been corrupted but it does not otherwise verify the file s authenticity The sfv file extension is usually used for SFV files 1 Simple file verificationFilename extension sfvInternet media typetext x sfvType of formatPlain text list of CRC32 checksums Contents 1 Checksum 1 1 Command line utility 2 See also 3 References 4 Further reading 5 External links 5 1 Windows onlyChecksum editFiles can become corrupted for a variety of reasons including faulty storage media errors in transmission write errors during copying or moving and software bugs SFV verification ensures that a file has not been corrupted by comparing the file s CRC hash value to a previously calculated value 1 Due to the nature of hash functions hash collisions may result in false positives but the likelihood of collisions is usually negligible with random corruption The number of possible checksums is limited though large so that with any checksum scheme many files will have the same checksum However the probability of a corrupted file having the same checksum as its original is exceedingly small unless deliberately constructed to maintain the checksum SFV cannot be used to verify the authenticity of files as CRC32 is not a collision resistant hash function even if the hash sum file is not tampered with it is computationally trivial for an attacker to cause deliberate hash collisions meaning that a malicious change in the file is not detected by a hash comparison In cryptography this attack is called a collision attack For this reason the md5sum and sha1sum utilities are often preferred in Unix operating systems which use the MD5 and SHA 1 cryptographic hash functions respectively Even a single bit error causes both SFV s CRC and md5sum s cryptographic hash to fail requiring the entire file to be re fetched The Parchive and rsync utilities are often preferred for verifying that a file has not been accidentally corrupted in transmission since they can correct common small errors with a much shorter download Despite the weaknesses of the SFV format it is popular due to the relatively small amount of time taken by SFV utilities to calculate the CRC32 checksums when compared to the time taken to calculate cryptographic hashes such as MD5 or SHA 1 SFV uses a plain text file containing one line for each file and its checksum 1 in the format FILENAME lt whitespaces gt CHECKSUM Any line starting with a semicolon is considered to be a comment and is ignored for the purposes of file verification The delimiter between the filename and checksum is always one or several spaces tabs are never used A sample SFV file is This is a comment file one zip c45ad668 file two zip 7903b8e6 file three zip e99a65fb Command line utility edit An example of an open source cross platform command line utility that outputs crc32 checksums is 7 Zip 2 Many Linux distributions include a simple command line tool cksfv to verify the checksums See also editCyclic redundancy check CRC File verification ParchiveReferences edit a b c Wang Wallace 2004 Steal this file sharing book what they won t tell you about file sharing ISBN 9781593270940 h Hash command 7 Zip May 23 2016Further reading edit SFV FAQ from isonews com SourceForge retrieved and archived 29 August 2021 External links editOnline SFV Calculator QuickSFV SFV checksum verifier Windows Vista or earlier and Linux wxChecksums Opensource Windows Linux application Check SFV SFV software for UNIX systems checkSum Mac OS X MD5 compatible free isfv sfv checksum verifier for Mac OS XWindows only edit RapidCRC Freeware application RekSFV SFV MD5 SHA1 utility Multi Language Unicode with batch mode for checking a huge amount of folders RapidCRC Unicode RapidCRC with Unicode support v0 3 4 as of 05 27 2012 supports UTF 8 with or without BOM and UTF 16 LE AmoK SFV Utility CRC32 and MD5 Compatible SFV Ninja SFV MD5 SHA 1 256 384 512 utility Freeware for personal use SFV Checker SFVManager SlavaSoft FSUM Fast File Integrity Checker HashCheck Shell Extension SFV MD4 MD5 SHA 1 Multi Language Total Commander supports creation and verification of SFV files hkSFV supports creation and verification of SFV files crashes on massive SFV files check DySFV Open Source free application for large files ilSFV free and open source SFV MD5 and SHA 1 file verification utility Retrieved from https en wikipedia org w index php title Simple file verification amp oldid 1184731682, wikipedia, wiki, book, books, library,
