The hash function is means a function that can be used to map data of a random size to data of a fixed size. That’s what it means when you hear people referring to “hashes”, “hash value” or “hash codes.” A hash function can be used in a hash table, which is a way to structure information so that software can have quick access to it. The hash function makes database access faster by detecting duplicated records in big files. Hash functions are also useful in cryptography. The cryptographic hash allows data that’s been entered to be verified by mapping it to certain hash values, and so when the input data isn’t known it’s very difficult to put it back together.
Hashing means the transformation of character strings into shorter character strings or keys of a fixed length which go in place of the original characters. This is what makes hashing so useful for database lookups, and obviously why it lends itself well to data encryption.
The hashed version of any text will always take up less space than the original. It’s constructed using a formula in such a way that the chances of another text ever resulting in the same hash value are vanishingly small. This is exactly why anyone sending a message to a security system that uses hashing can effectively render it immune to tampering.
In this case the person sending the message creates a hash of it that encrypts it. The hash and the message are sent to the recipient, who then needs to decrypt the hash and the message. They will then generate another hash from this received message and compare the two hashes. If they both match, then this proves that there is virtually no chance that the message was tampered with en route.