So ever since I first took a stab at understanding stream Ciphers, not one stood out more than RC4, because it's so fantastically simple. As most people reading this will know, with its fantastic simplicity comes with easily done cryptanalysis and RC4 has certainly been subject to plenty of it (leading to RC4's total failure, more or less).
Now, when breezing over the wikipedia article on alternative constructions of the PRGA stage of RC4, we get this rather neat little alteration, dubbed spritz:
#// All arithmetic is performed modulo 256 while GeneratingOutput: i := i + w j := k + S[j + S[i]] k := k + i + S[j] swap values of S[i] and S[j] output z := S[j + S[i + S[z + k]]] endwhile
Now a bunch of things spring to mind about this alteration (that is seemingly far stronger, albeit, unfortunately much slower) but what's at the forefront of my mind is:
THREE Specific questions I'd like to know the answer to are:
Can we safely assume that from any given setup of S, we can get to another set up of s? Or does it follow, that there will be some impossible states, like the Finney States of RC4?
Can anybody actually link me to any paper attempting any cryptanalysis of spritz, being as a DRBG, Stream Cipher or Cryptographically Secure Hash?
Finally: I know the question should be more specific: But given it's similarity to RC4? How many problems from RC4 could we expect to pop-up in Spritz?
There's a few questions here, the reality is I'd be grateful to get an answer on any of these, as papers on this algorithm, don't seem to be an easy google search away... but my own limited tests (and thought experiments), make me think we're certainly onto a better version the PRGA for RC4 (apart from the fact, it's 40-50% of the speed).
All input appreciated!
(edit: I removed the question about what values of W can we use: the answer is 1..3..5..7, up to 255, presuming the range of S, is 256)