[cryptography] Compositing Ciphers?

Tony Arcieri bascule at gmail.com
Sat Sep 14 00:53:18 EDT 2013

On Fri, Sep 6, 2013 at 5:53 PM, Natanael <natanael.l at gmail.com> wrote:

> Apparently it's called "cascade encryption" or "cascade encipherment"

More generally it's known as a product cipher, which underlies things like
Feistel Networks which were used to compose algorithms like DES:


If A1 and A2 are secure PRGs, and we encrypt message m under the keystream
of A1(k1) ⊕ A2(k2) [where k1 and k2 are unrelated randomly generated keys],
the resulting cipher is at least as strong as the strongest of the two
ciphers. This can provide a failsafe if a cryptanalysis is found for either
of the two ciphers.

Tony Arcieri
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