3 ms·
> While there are also modes of operation (like OFB and CFB) that can produce self-synchronizing stream ciphers, these are far less common, and not discussed he
by Mindless2112 13y ago
> While there are also modes of operation (like OFB and CFB) that can produce self-synchronizing stream ciphers, these are far less common, and not discussed here.
Aw. :( Aren't there any noteworthy attacks against these modes?
- pbsd 13y agoWhile CFB can be considered a self-synchronizing stream cipher, OFB is a typical synchronous stream cipher. Being stream ciphers, these modes suffer from the usual bit-flipping attacks and nonce-reuse problems, same as CTR. One problem specific to these feedback modes (and also to sponge functions) is the possibility of falling into a short cycle. A random permutation is expected to have log n cycles, with one big cycle taking around half of the values and a few shorter ones. Falling into a short cycle would imply quickly repeating the stream, which is catastrophic. The good news is that for a good block cipher the probability of this happening is overwhelmingly small, i.e., 1/2^(n-1) for block size n.