Re: the meaning of linearity, was Re: picking a hash function to be encrypted

2006-05-18 Thread Travis H.
On 5/18/06, Travis H. <[EMAIL PROTECTED]> wrote: ... There's 255 "other" permutations, so the chance that there is at least one k' such that f_k'(x)=y is 255/256 = 99.6%. The chance that there is exactly one such k' is sampling with replacement and if I am not mistaken P(|K|=1) = (255/256)^255 =

Re: the meaning of linearity, was Re: picking a hash function to be encrypted

2006-05-18 Thread Travis H.
On 5/17/06, Kuehn, Ulrich <[EMAIL PROTECTED]> wrote: Given known plaintext and corresponding ciphertext, there should not be too many keys that map the plaintext to the ciphertext. I don't have the probability at hand how many such 'collisions' you would expect from 256 random permutations, bu

RE: the meaning of linearity, was Re: picking a hash function to be encrypted

2006-05-17 Thread Kuehn, Ulrich
> -Original Message- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > > The thing I've always wondered about stream ciphers is why we only > talk about linear ones. A stream cipher is fundamentally constructed > of two things: A stream of bits (alleged to be unpredictable) as > lo

Re: the meaning of linearity, was Re: picking a hash function to be encrypted

2006-05-15 Thread James Muir
Travis H. wrote: - Stream ciphers (additive) This reminds me, when people talk about linearity with regard to a function, for example CRCs, exactly what sense of the word do they mean? I can understand f(x) = ax + b being linear, but how exactly does XOR get involved, and are there +-linear fu

Re: the meaning of linearity, was Re: picking a hash function to be encrypted

2006-05-15 Thread Travis H.
On 5/15/06, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: Other than post by a guy - Terry someone or another - on sci.crypt a number of years ago - I've never seen any work in this direction. Is there stuff I'm not aware of? That would probably be Terry Ritter, www.ciphersbyritter.com. He call

Re: the meaning of linearity, was Re: picking a hash function to be encrypted

2006-05-15 Thread leichter_jerrold
| > - Stream ciphers (additive) | | This reminds me, when people talk about linearity with regard to a | function, for example CRCs, exactly what sense of the word do they | mean? I can understand f(x) = ax + b being linear, but how exactly | does XOR get involved, and are there +-linear function

the meaning of linearity, was Re: picking a hash function to be encrypted

2006-05-14 Thread Travis H.
- Stream ciphers (additive) This reminds me, when people talk about linearity with regard to a function, for example CRCs, exactly what sense of the word do they mean? I can understand f(x) = ax + b being linear, but how exactly does XOR get involved, and are there +-linear functions and xor-li