4 ms·
Cipher cascades have been proven to be at least as strong as the strongest cipher, but only if you use commutative encryption - multiple stream ciphers (and/or
by ryan-c 11y ago
Cipher cascades have been proven to be at least as strong as the strongest cipher, but only if you use commutative encryption - multiple stream ciphers (and/or block ciphers in counter mode) xor'd together. Truecrypt did not use this construction.
- nickpsecurity 11y agoThere we go! Been a while since the last positive comment on this. :)
- ryan-c 11y agoMy opinion on cascade ciphers is currently neutral. If done properly, they are a nice hedge against currently unknown weaknesses, but a more complicated construction means more places to make mistakes.
- nickpsecurity 11y agoThat's why I used them. There could be obscure, mathematical interactions that they introduce that are problematic. We might eventually figure those out. The enemy might be able to exploit those without knowing which ciphers, which order, and which initial data. Meanwhile, there's a steady stream of problems in regular ciphers, modes, and protocols that justify mitigating any one in a design. So, yeah, my polyciphers are a hedge. They also exploit combinatorial explosion by randomizing extra, large numbers. Used to by resources required to simulate the combos of algorithms themselves but FPGA's made that obsolete. :(
- baby 11y agoSo it should be AT LEAST as strong as the first cipher used in the chain. This is still a good reason to use cascade.
- ryan-c 11y agoThe paper that proves this, is actually called "Cascade Ciphers: The Importance of Being First". http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.36.5309&rep=rep1&type=pdf http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.36....