Cryptographic hash functions are one way functions that take some input and produce a pseudorandom output.
We say pseudorandom because, while it appears random to us, it is actually always going to be the same output for some given input.
In other words, if I take the hash of “hello, world!” once, it will be the same if I do it a second time.
This is necessary for standardization between all parties.
A cryptographic hash function always outputs a message of some given size.
One note is that we call the output the image, and the input the pre image.
Cryptographic hash functions differ from regular hash functions in that they are built for security, but for convenience, we will now refer to cryptographic hash functions as hash functions.