Write a short note on Message Digest (MD) hash function.

A Message Digest (MD) hash function is like a secret code for messages. It takes in any message and turns it into a fixed-size jumble of letters and numbers, called a digest. This digest is like a unique fingerprint for the original message, making it useful for checking if the message has been altered or tampered with.

Think of it like a digital signature for your message. You can use this digest to verify if the message is authentic, just like you might use a signature to confirm the identity of a person.

Now, MD hash functions are good at this authentication job, especially for digital signatures. However, the older versions of MD have been retired for most security tasks, except for simple jobs like checking if data got messed up by accident.

The main goal of these hash functions is to make the digest seem random. This randomness is crucial for security. To be super secure, a hash function needs to meet two big rules: first, it should be practically impossible for someone to create a fake message that matches a specific digest, and second, it should also be practically impossible for someone to create two different messages that end up with the same digest.