The FISH stream cipher

Stream cipher

In cryptography, a stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream . In a stream cipher the plaintext digits are encrypted one at a time, and the transformation of successive digits varies during the encryption...

 is a fast software based stream cipher using Lagged Fibonacci generator

Lagged Fibonacci generator

A Lagged Fibonacci generator is an example of a pseudorandom number generator. This class of random number generator is aimed at being an improvement on the 'standard' linear congruential generator...

s, plus a concept from the shrinking generator

Shrinking generator

In cryptography, the shrinking generator is a form of pseudorandom number generator intended to be used in a stream cipher. It was published in Crypto 1993 by Don Coppersmith, Hugo Krawczyk, and Yishay Mansour....

 cipher. It was published by Siemens

Siemens AG

Siemens AG is a German multinational conglomerate company headquartered in Munich, Germany. It is the largest Europe-based electronics and electrical engineering company....

 in 1993. FISH is quite fast in software and has a huge key length. However, in the same paper where he proposed Pike

Pike (cipher)

The Pike stream cipher was invented by Ross Anderson to be a "leaner and meaner" version of FISH after he broke FISH in 1994; the name is a humorous allusion to the Pike fish. The cipher combines ideas from A5 with the Lagged Fibonacci generators used in FISH. It is about 10% faster than FISH, yet...

, Ross Anderson showed that FISH can be broken with just a few thousand bit

Bit

A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...

s of known plaintext

Plaintext

In cryptography, plaintext is information a sender wishes to transmit to a receiver. Cleartext is often used as a synonym. Before the computer era, plaintext most commonly meant message text in the language of the communicating parties....

.