Are [crc] questions on-topic here, and should they be?

Question

Thanks to a recent question, I realized that we have a crc tag, with 17 questions and the following tag wiki excerpt (quoted verbatim):

The Cyclic Redundant Check is non-cryptographic error-detecting code commonly used to detect accidental changes to raw data.

Given that even the tag wiki describes CRC as "non-cryptographic", the question arises whether any of these questions are really on-topic here, and (even if some of them are) whether we really should have a tag for something that seems to be explicitly off-topic here.

Now, granted, I can certainly imagine CRCs appearing as a part of a cryptosystem, or otherwise being tangentially mentioned in a valid, on-topic question. But, even though error-checking codes certainly are a pretty close topic to crypto, and even though some of the past CRC questions have received good answers here, I don't really see how a question primarily about CRCs could be on-topic here. Unless, of course, we just decide that they are — after all, the scope of the site is ultimately up to the community.

Given all that, I'd like to ask the community's opinion on the following issues:

1. Should most of the questions currently tagged with crc be closed as off-topic (and what are the exceptions, if any)?

2. If the answer to the previous question is "yes", what should we do with the tag itself? Should we remove it, to keep it from attracting further off-topic questions, or should we leave it in place and just add a warning that "questions primarily about CRCs may be off-topic here"? Or something else?

Answer 1

CRC is a non-cryptographic checksum function, so it actually doesn't belong on Crypro.SE.

Our help center currently states:

Cryptography Stack Exchange is for asking questions about the mathematics and properties of cryptographic systems, their analysis ("cryptanalysis") and subsidiary topics that generally make up cryptology, such as random number generation. As such, we welcome questions on topics such as:

• Asymmetric and symmetric cryptographic algorithms
• Cryptographic protocols
• Cryptanalysis techniques
• Cryptographic hash functions, cryptographically secure hashing
• Cryptography- and/or cryptanalysis-related Entropy and information theory
• Cryptographically Secure (Pseudo-)Random Number Generation

I don't really see how CRC (being a non-cryptographic checksum function) would fit it there. Only when questions go (for example) "CRC vs SHA1", mentioning/handling CRC makes sense.

If we want to generally include all questions about error detection functions and other non-cryptographic types of checksums, we should reconsider our general theme (currently being cryptography) as well as several related help-center descriptions. Something tells me we don't want to go there... we're a site dedicated to cryptography and cryptanalysis; not a mixed-purpose Stack Overflow kind of site. If we were, we would most probably have been called "Algorithms.SE" or something alike. Yet, we're Crypto.SE - a clear name that says it all!

Last but not least, it should be noted that questions about CRC tend to find a nice home at Stack Overflow, just like checksums in general.

Edit: As the recent migration shows, people like Mark Adler tend to check such Q&As at SO - so, things like CRC definitely have a safe haven at Stack Overflow!

Answer 2

I think it is pretty obvious that questions that are just about CRC are not on topic here. The problem is of course that it would not even be clear to me where they should belong. Definitely not on math, security or cryptography. StackOverflow maybe, but it isn't directly related to programming sometimes. Computer Science could be a good last option.

There are quite a few questions for the tag that are related to cryptography. E.g. when CRC is mixed with crypto or when CRC is used as a poor mans authentication tag then sure, by all means, please post here. And that's in my opinion a good reason to keep the tag as well. It would for such topics of course be a good idea to make sure that this kind of requirement is clearly documented within the tag description.

Some other questions should have been closed already, and I would invite the mods to take a good look at a few of them. Even if they don't do much harm in themselves they do lead to fingerpointing by authors of questions that become closed.

Answer 3

I present a counterexample to the proposition that the concept of CRCs is inherently non-cryptographic.

(This does not imply the cryptographic application is useful, of course! But who knows, maybe there are CRC circuits admitting arbitrary generator polynomials out of which one must implement a protocol on a tiny hardware device.)

Answer 4

It's part of a wider debate.

Some might argue that the design of TRNGs has nothing to do with cryptography either but they are often discussed here in great, lengthy detail. If you're willing to accept TRNGs , you'd have to accept CRC functions here too as they're often used as either the sole entropy extraction algorithm, or in combination with others. The TrueRNG uses Galois field mixing which is similar to CRCs. And NIST supports TrueRNG in their entropy measurement tool set so that must be pretty official given the thrall of NIST. IDQ Quantique uses similar matrix methods. OneRNG, NeuG and other more DIYey efforts use CRC16/32. But most importantly, the mathematics of entropy mean that CRC computation is a perfectly valid form of extraction, especially if you're not a NIST fanboi.

So if crypto.SE -> TRNG -> entropy -> extraction, I say leave it in.