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Hot answers tagged alternating-step

12

A stream cipher, RSA, or whatever you designate by the expression "discrete logarithm system", are not "one-way functions". In particular, asymmetric encryption algorithms and digital signature algorithms provide functionality which is not doable (or not with the same usability) with only the "scrambling" techniques of symmetric cryptography. Let's not ...

4

Okay, I had a look at your source [12], e.g. ON EDIT DISTANCE ATTACK TO ALTERNATING STEP GENERATOR. The original ASG defines the key stream Z = {z_i} from three shift registers X = {x_i}, Y = {y_i} and C = {c_i} via these steps: Initially, l = 0, t = 1. If ct = 1, then l = l + 1; Output z_t = x_l ⊕ y_(t−l) , where ⊕ is XOR operator; t = t + 1 ...

4

Some points on the Wikipedia entry: in the overview: However, they cannot be used as-is because their output can be predicted easily. and in the security section: In Reduced Complexity Attacks on the Alternating Step Generator, Shahram Khazaei, Simon Fischer, and Willi Meier give a cryptanalysis of the ASG allowing various tradeofs between time ...

4

But he did get a US patent for it: Generator for generating binary ciphering sequences In fact, it looks very similar to A5/1 and 2 which were used in the GSM spec. The designers of A5/1 were doubtless aware of the ASG paper as it was presented in Europe the very same year. It would be really interesting to find out if they licensed it or simply worked ...

3

If it hasn't been cracked since 1987, why is it not considered to be a candidate for a "one way function" like the RSA crypto system, the discrete logarithm system, etc.? This generator looks like suitable for a stream cipher, i.e. it is a one-way function (of type N -> *, i.e. fixed length input, variable-length output.) Other common ...

2

A de Bruijn Sequence, as defined in N.G. de Bruijn's A combinatorial problem, Proc. K. Ned. Akad. Wet., vol. 49, pp 758-764, 1946 (with attribution to Ir. K. Posthumus) is an ordered cycle of $2^n$ digits 0 or 1, such that the $2^n$ possible ordered sets of $n$ consecutive digits of that cycle are all different. The example given for $n=3$ is the ...

1

The question as stated has some serious issues: The alternating step generator works with 3 LFSRs. If the output of R1 is 1, then R3 is clocked, otherwise R2 is clocked, so at each clock period exactly one of those two is clocked. The output of R2 and R3 is added modulo 2 to form the keystream. The initial loadings of the 3 LFSRs is essentially the key. ...

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