In this tutorial we'll build a cyclic redundancy check (CRC) hashing function. More specifically, its 32 bit variant called "CRC-32". I bumped into it in the PNG specification, but it's also used in Gzip and bunch of other formats and protocols. In short, it makes a tiny (4 bytes) hash out of whatever binary data you feed to it and changes significantly if data changes even slightly. Of course, such a tiny function is not even close to be crypto secure, therefore it's only used to check if data was transferred correctly.