Editing Pike (cipher)

{{Short description|Stream cipher}}
The '''Pike''' [[stream cipher]] was invented by [[Ross J. Anderson|Ross Anderson]] to be a "leaner and meaner" version of [[FISH (cipher)|FISH]] after he broke FISH in 1994. Its name is supposed to be a humorous allusion to the [[Pike (fish)|pike fish]].

The cipher combines ideas from [[A5 (cryptography)|A5]] with the [[lagged Fibonacci generator]]s used in FISH. It is about 10% faster than FISH, yet believed to be much stronger. It potentially has a huge [[key length]], and no attacks have been published {{As of|2004|lc=on}}.

== Inner workings ==

Pike consists of three [[lagged Fibonacci generator]]s with relations
<math display="block"> \begin{align}
a_i = a_{i-55} + a_{i-24} \ (mod \ 2^{32}) \\[]
b_i = b_{i-57} + b_{i-7} \ (mod \ 2^{32}) \\[]
c_i = c_{i-58} + c_{i-19} \ (mod \ 2^{32})
\end{align}
</math>

The clock control is based on the carry bits.
If all carry bits agree we step all three LFG's, otherwise we step the two who do agree.

This control will be delayed 8 cycles.
The final output is the XOR of the least significant words of all three generators.

== External links ==
* [https://www.iacr.org/cryptodb/data/paper.php?pubkey=2963  ''Ross Anderson, «On Fibonacci Keystream Generators»''], 1994.
* [https://www.cl.cam.ac.uk/~rja14/Papers/fibonacci.pdf ''On Fibonacci Keystream Generators''], Ross Anderson, 27-Jul-2006.

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