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seen Jan 7 at 16:10

Sep
16
awarded  Nice Answer
Aug
18
awarded  Yearling
Aug
29
awarded  Scholar
Aug
29
accepted Hamming Distance vs. Index of Coincidence
Aug
29
comment Hamming Distance vs. Index of Coincidence
I mean, given a single XOR, of course. Hamming's wouldn't work at all on a Vignere, because the CT would be all letters, the keys wouldn't affect the Hamming weights...
Aug
29
comment Hamming Distance vs. Index of Coincidence
Is length of CT another factor? Would Hamming distance perform better on shorter CTs, since you may not have enough columns to get a reliable IoC?
Aug
28
awarded  Student
Aug
28
asked Hamming Distance vs. Index of Coincidence
Aug
26
revised Is AES-XTS considered safe to encrypt multiple files with the same keys?
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Aug
26
answered Is AES-XTS considered safe to encrypt multiple files with the same keys?
Aug
26
awarded  Commentator
Aug
26
comment RC2, RC4, RC5 key length
I like this answer, because it gets right to the point, unlike that other long-winded guy. :)
Aug
26
revised RC2, RC4, RC5 key length
Edited for precision, in light of DW's comments. Related keys are not as scary as I made out. :)
Aug
26
comment RC2, RC4, RC5 key length
I appreciate the feedback, I def need to increase my precision here. For the record, both Grosul and Miyaji agree that the difficulty of finding related key families (under some definitions of related keys) is inversely proportional to the key size. It's a strange effect, I know, but it relates to the strange relationship between periodicity and key size, as well as the fact that small keys are repeated to fill the key array, such that any small change is actually propagated multiple times. I really recommend checking out their findings. Yeah, outside the scope, though I'll edit.
Aug
26
comment RC2, RC4, RC5 key length
"Proper" RC4 is so easy? Sure, hash your key + IVs, that's why I cited Rivest's recommendations originally. That's not going to be practical for all implementations though. Per the refs, shorter keys make key collision searches impractical (barring chosen PT, like in the WEP crack, ie, completely different). Even so, the related keys aren't the only issue here. The PRNG doesn't have as many initial states as there are keys. At best, long keys are just providing a false sense of security. It's the same as providing more than 2048 bits, most of your information is just getting tossed anyway.
Aug
25
comment RC2, RC4, RC5 key length
Also, for very long keys, there are families of related keys that produce similar results for the first several 100 Bytes of keystream. The recommended patch is to discard a bunch of your initial keystream bytes before that normalizes, though I think there's ongoing debate as to how many, or if there are similar families of related keys that are much smaller. pubs.cs.rice.edu/sites/pubs.cs.rice.edu/files/…
Aug
25
comment RC2, RC4, RC5 key length
It was practical, Chen and Miyaji recovered an 86 Byte key using a standard desktop computer in about 20 hours. The weakness comes from the fact that the number of possible states for the initialized array is so much smaller than the possible keys. So when you provide a long key, it is almost always producing the same initial state as some other key. Matsui's 'Key Collisions of the RC4 Stream Cipher' provides a good overview of this class of attacks.
Aug
25
answered Implementing a one-time pad without binary?
Aug
25
revised RC2, RC4, RC5 key length
removed hedging in order to correct an ambiguity
Aug
25
answered RC2, RC4, RC5 key length