In the USA, the National Institute for Standards and Technology (NIST) have been looking for a replacement for the now ageing Data Encryption Standard algorithm (DES). I suspect that they thought when DES was first introduced that it would last for most of their lifetimes. However the increasing computing power available to even the private citizen makes the days of DES providing acceptable security very much numbered.

The process instigated by NIST to find AES (Advanced Encryption Standard) is a multi-round one in which candidates are eliminated and the remainder have time to refine their work. The Twofish Encryption Algorithm is one of the contenders.

As a lot hangs on becoming the successful candidate, each team spends much time trying to find weaknesses in their rivals algorithms. This is actually a desirable feature of this competition because the ultimate winner needs to be robust against attacks from hardware a couple of orders of magnitude faster than anything available today. Even the hint of a route to successfully cracking a cipher needs to be known. Ultimately other criteria will also be taken into account including the ready availability of software and experience in using the algorithm.

If you want to find out about Twofish, read this book. If you want a copy of its implementation in C go tohttp://www.counterpane.com/twofish.html. Do not bother with this book if you are not competent in the theory of encryption algorithms.