After explaining what a hash function is, we will deal with MD5 and then the SHA family: SHA-1, SHA-2, and SHA-3. We will also acquire a bit of information about cracking hashes.
As mentioned earlier, one point of using hashes is to put a fingerprint on a file. You can take all the bytes in the file and combine them together with a hash algorithm, and this creates a fixed-links hash value. If you change any part of the file and recalculate the hash, you get a completely different value. So, the idea is that if you have two files that are supposed to be identical, you can calculate the hash of each file, and if the hash of both files match, then the files are identical.
A very common hash is MD5; it's been around for a couple of decades. It's 128 bits long, which is rather short for a hash function, and it's reliable enough for most purposes. People use it to put a fingerprint on downloads, and malware samples, and all sorts of things, and they are also sometimes...