Comparison of file verification software

The following tables compare file verification software that typically use checksums to confirm the integrity or authenticity of a file.

General

There were several different file verification technologies, at this writing, including Simple File Verification (SFV), Message-Digest algorithm 5 (md5), Secure Hash Algorithm 1 (sha1), and Checksum. A number of computer programs incorporated these technologies, in various ways. The common goal, in general terms, was to use the data within a file to calculate a number. A very simple example, simpler than the one at the foregoing Wikipedia link for Checksum, would arise where one combined the numerical value of letters together. In the string "adb," for instance, the letter "a" would have a value of 1, because it comes first in the alphabet; "d" would have a value of 4; and "b" would have a value of two. If the algorithm in question called for adding the first two letters and subtracting the third, the result would be 1 + 4 - 2 = 3. If one of the letters got changed, the result would not be 3 anymore. A person could store the value of 3, with that "adb" string, and could re-run the calculation at any time to make sure the string's contents had not changed. More complex algorithms, based upon large quantities of data within a file, significantly reduced the possibility that part of a file could change without also changing the resulting value. So, for these technologies, the basic idea was that one would calculate the sum when the file was created; would keep that sum with the file; and would refer back to it whenever one wanted to verify that the file had not changed.