[Cryptography] Why prefer symmetric crypto over public key crypto?

Jaap-Henk Hoepman jhh at cs.ru.nl
Sun Sep 8 08:10:09 EDT 2013

> Symetric cryptography does a much easier thing. It combines data and some mysterious data (key) in a way that you cannot extract data without the mysterious data from the result. It's like a + b = c. Given c you need b to find a. The tricks that are involved are mostly about sufficiently mixing data, to make sure there's enough possible b's to never guess it correctly and that all those b's have the same chance of being the one b. Preferably even when you have both A and C, but that's really hard. 
> So I'd say Bruce said that in an effort to move to more well understood cryptography. It is also a way to move people towards simply better algorithms, as most public key systems are very, very bad.

Funny. I would have said exactly the opposite: public key crypto is much better understood because it is based on mathematical theorems and reductions to (admittedly presumed) hard problems, whereas symmetric crypto is really a black art that mixes some simple bit wise operations and hopes for the best (yes, I know this is a bit of caricature...)


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