SFV

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SFV is an abbreviation for simple file verification, a checksum format using the CRC32 algorithm to verify the integrity of files.

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Check sum

Files can become corrupted for a variety of reasons including: faulty storage media, errors in transmission, write errors during copying or moving, and so on. SFV allows a person to ensure that a file has not become corrupted by comparing a hash applied a file to see that they are equal. SFV also allows users to verify the authenticity of files, since if a file was changed (say, with the addition of malicious code) the hash 'fingerprint' of the file would change and alert the user that the authenticity of the file is in question.

One of the first programs to use the SFV format was WinSFV.

SFV uses a plain-text file containing one line for each file and its checksum in the format FILENAME CHECKSUM. Any line starting with a semicolon ';' is considered to be a comment line and is ignored for the purposes of file verification. A sample SFV file appears as follows: 

file1.zip c45ad668
file2.zip 7903b8e6
file3.zip e99a65fb
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Flaws

The hash function used by SFV, CRC32, is not a cryptographically secure hash function. It is easy to intentionally create a file with a given CRC32 checksum. The fact that a file's checksum corresponds with the checksum in the SFV file is therefore no guarantee that the file has not been tampered with. However, SFV is well suited to detect 'random' changes.

Other hash functions, such as SHA, are better suited for ensuring the authenticity of files. But this is only helpful if there is a secure second channel to get the checksums.


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External links

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