# Tag Info

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. ...

0

Note: I won't recommend a specific library for these, because this would be off-topic and the risk would be there that this gets outdated sooner than later (especially as soon as CAESAR finishes). This is a very standard solution to the authentication problem although usually one does do both (e.g. passphrase and keyfile). On the conceptual level any ...

0

The security - assuming you can validate the correctness of $K$ - is 56 bits (not even counting any attacks on DES itself, assuming to test all keys). This is because you can brute force $K_{BT}$ without even looking at $K_{AT}$ in your particular scheme. 2 key triple DES on the other hand would at least offer over 80 bit security. So this scheme is ...

3

It's a matter of periods in the sequence of numbers generated by the PRNG. If the output of the PRNG has a single period that is of length $2^n$, then you can avoid repetition by appropriately recording the section that you have already used. Thus if you start from $0$ and get the first time to $g_1$, the next time you start from $g_1$ and get to $g_2$, etc. ...

0

It's still just a substitution cipher. The fact that it maps to a (somewhat) different alphabet doesn't change that. You could still perform frequency analysis to retrieve the plaintext. Of course you'd have a rather large (26 character) key if the attacker doesn't find out that you're using the QUERTY keyboard layout. But a bit of puzzling would be enough ...

0

I think the attack models establish constraints on the cipher parameters that allow you to confirm guesses in a brute force or probabilistic search. A simple way to look at it is that they let your write equations involving the cipher parameters. For example, in $c = enc(p,k)$, you can fix two of the parameters and solve for the third. Clearly $c$ ...

1

I did not know the scheme, so I had to google it to find the missing part of its description - here it is, in case someone else wants it. So, two keys are in the same equivalence class when they have the same $\gamma_1$ and $\gamma_2$, id est, when $\alpha^{a_1}\beta^{a_2} = \alpha^{a'_1}\beta^{a'_2} \bmod p$, and \$\alpha^{b_1}\beta^{b_2} = ...

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