Lessons

Secrecy for arbitrary data that can't be protected physically can be obtained by scrambling it so that you need to know some secret to unscramble it.

This is what most people think of when they think of cryptography, but it's only a solution to half of the problem. (Why?)

Authentication is a more complicated problem to get one's head around. The idea is to create a messaging system in which a given message can be absolutely identified as coming from a specific individual. Exactly how to go about doing that is a function of the system's design, though some variation of a hash is popular.

Does authentication necessarily mean a loss of privacy?

cryptography metaphors secrecy authentication
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