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    <p>Despite what other users answered, <strong>CRC32 is not a cryptographic hash function</strong>; it is meant for integrity checks (data checksums). Cryptographic hash functions are often described as "one-way hash functions", CRC32 lacks the "one-way" part.</p> <p>That being said, you should consider the following: since the set of all possible 25-characters-or-less filenames is more than 2^32, some file names are bound to have the same hash value. Therefore, it might be that for some of the CRC32 values you get - there will be several possible sources (file-names). You will need a way to determine the "real" source (i assume that human-decision would be the best choice, since our brain is a great pattern-recognition device, but it really depends on your scenario).</p> <p>Several methods can be used to partially achieve what you are asking for. <strong>Brute-force</strong> is one of them (although, with 25 characters long file names, brute-force may take a while). A modified <strong>dictionary attack</strong> is another option. Other options are based on analysis of the CRC32 algorithm, and will require that you dive into the implementation details of the algorithm (otherwise you'll have a hard time understanding what you're implementing). For example, see this <a href="http://www.codebreakers-journal.com/downloads/cbj/2004/CBJ_1_1_2004_Anarchriz_CRC_and_how_to_Reverse_it.pdf" rel="nofollow noreferrer">article</a>, or this <a href="http://sar.informatik.hu-berlin.de/research/publications/SAR-PR-2006-05/SAR-PR-2006-05_.pdf" rel="nofollow noreferrer">artice</a>.</p> <p>EDIT: definitions by Bruce Schneier (author of Applied Cryptography, among other things):</p> <blockquote> <p>One-way functions are relatively easy to compute, but significantly harder to reverse. … . In this context, "hard" is defined as something like: It would take millions of years to compute x from f(x), even if all the computers in the worlds were assigned to the problem.</p> <p>A hash function is a function, mathematical or otherwise, that takes a variable length input string and (called a pre-image) and converts it to a fixed length (generally smaller) output string (called a hash value).</p> <p>The security of a one-way hash function is its one-wayness.</p> </blockquote>
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    1. POcrc32 decrypt short string
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    1. COWith this description, all hash algorithms are "lacking the one-way part", as you can always run brute-force on data to find which one(s) are producing the desired outcome. I would very much like you to describe why CRC32 lacks the "one-way" part, and, say, SHA384, doesn't.
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      1. USLasse Vågsæther Karlsen
    2. COI didn't define the "one-way" part. If you consider brute-force, then everything is insecure except for One Time Pads and derived algorithms (like some secret-sharing schemes). The "one-way" part depends on the algorithm being "hard to reverse", meaning that given an image it is hard to learn anything about the source. Being "one-way" is not a well-defined criterion; it depends on current research and study of the algorithm. It can change, based on new knowledge spreading through the research community. CRC was never built to be "one-way", the designers didn't try to make it that way.
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    3. COhttp://en.wikipedia.org/wiki/Hash_function http://en.wikipedia.org/wiki/Cryptographic_hash_function see the difference?
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