File containing its own checksum

Question

Is it possible to create a file that will contain its own checksum (MD5, SHA1, whatever)? And to upset jokers I mean checksum in plain, not function calculating it.

Answer 1

You can of course, but in that case the SHA digest of the whole file will not be the SHA you included, because it is a cryptographic hash function, so changing a single bit in the file changes the whole hash. What you are looking for is a checksum calculated using the content of the file in way to match a set of criteria.