When is CRC more appropriate to use than MD5/SHA1?

Question

When is it appropriate to use CRC for error detection versus more modern hashing functions such as MD5 or SHA1? Is the former easier to implement on embedded hardware?

Answer 1

Only use CRC if computation resources are very tight (i.e. some embed environments) or you need to store/transport many output values and space/bandwidth is tight (as CRCs are usually 32-bit where an MD5 output is 128-bit, SHA1 160 bit, and other SHA variants up to 512 bit).

Never use CRC for security checks as a CRC is very easy to "fake".

Even for accidental error detection (rather than malicious change detection) hashes are better than a simple CRC. Partly because of the simple way a CRC is calculated (and partly because CRC values are usual shorter than common hash outputs so have a much smaller range of possible values) it is much more likely that, in a situation where there are two or more errors, one error will mask another so you end up with the same CRC despite two errors.

In short: unless you have reason not to use a decent hash algorithm, avoid simple CRCs.