[Cryptography] What is the difference between a code and a cipher?

Dave Horsfall dave at horsfall.org
Fri Sep 5 00:01:13 EDT 2014


On Thu, 4 Sep 2014, Richard Outerbridge wrote:

> Codes can have variable length plaintext symbols, and also variable 
> length ciphertext symbols.
> 
> Ciphers have same length plaintext symbols, but can have variable length 
> ciphertext symbols.

And coming as I do from a military family, it's also a way of abbreviating 
your message.  Look at ships' flags, for example.

"I am carrying explosives" i.e. try not to ram me.
"I have lost control of all steering" i.e. I might ram you in turn.
"I am carrying infectious diseases" i.e. don't even think about it.

And of course, there's the "England expects" truncation.

It's crypto, in a way.

-- Dave


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