Unlocking an 18th century Italian safe - GIF

[mklotz]

Secure safes, secret messages, computer passwords - the secret is the algorithm, not the key elements.

Here having all the keys doesn't immediately grant access; one has to know the algorithm, how and where to use the keys and the order in which they are employed.

The German Enigma machine was similar. The keys were the letters of the alphabet; known to everyone. The secret was the algorithm the machine employed to translate a plain text letter into an encrypted one. Changing the algorithm with each letter just makes it incredibly more difficult to analyze.

A similar algorithmic approach can be used to generate passwords that are easy for the user to remember but difficult to decipher, even if a fragment of the password is known to the intruder.