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The experience in the cryptanalysis field shows that evaluating the security level of a cryptosystem involves not only understanding the mathematical concept, but also applying the best possible cryptographic attacks on this cryptosystem by using the best available techniques. By applying the appropriate attack on the appropriate hardware platform, we can determine the security limits of the studied cryptographic algorithm, and this will enable us to recommend adjustments to the related parameters of this algorithm. On the other hand, although ordinary computers are capable of performing security services, cryptanalytical tasks may require massive computations that go beyond the capabilities of the available computing platforms and this raises the need of using high-performance platforms. In this paper, we will present a comparison between the most popular high-performance computing systems used to perform cryptanalytical tasks. This study will be of a particular interest to researchers who are interested in using high-performance computing units for testing cryptographic systems.

Cryptography can be defined as the art of secret writing or protecting information by transforming it (encrypting it) into an unreadable format, called cipher text and then transmitting it across insecure networks, so that it cannot be read by anyone except the intended recipient. Only those who possess a secret key can decipher (or decrypt) the message into plain text. Encrypted information can sometimes be broken by cryptanalysis, also called code breaking, although modern cryptography techniques are virtually unbreakable. Various algorithms help achieve flawless encryption results which are mostly unbreakable. This paper is an attempt to improve one such algorithm, i.e. RC6 by adding on to its existing functionalities.

We investigate the use of Markov Chain Monte Carlo (MCMC) methods to attack classical ciphers. MCMC has previously been used to break simple substitution ciphers. Here, we extend this approach to transposition ciphers and to substitution-plus-transposition ciphers. Our algorithms run quickly and perform fairly well even for key lengths as high as 40.

In 1944 a computer was commissioned at Bletchley Park in England. This computer was designed specifically to find the settings used by German cipher machines to encrypt messages, which it did very effectively. Before "Colossus" the Polish and British military had developed mechanical machines to aid with cryptography. All of this work was top secret and only with the recent release of documents has the true significance of these machines and the people who created them been appreciated.

Detta arbete är ett examensarbete i matematik på kandidatnivå vid Växjö universitet. Det är en studie av kodningsteori i allmänhet med fokusering på cykliska koder och Reed-Solomon-koder i synnerhet. Reed-Solomon-koderna används för att skapa McElieces kryptosystem. En kortfattad analys av McElieces kryptosystems säkerhet görs tillsammans med en genomgång av kända sätt att forcera denna typ av kryptosystem. Här visar det sig att användning av Reed-Solomon-kod försvagar kryptosystemet i förhållande till om den ursprungligt föreslagna Goppa-koden används. För att kunna göra denna säkerhetsanalys görs också en kortfattad genomgång av komplexitetsteori och vad det innebär att ett problem är NP-fullständigt. Nyckelord: Kodningsteori, Kodteori, Cykliska koder, BCH-koder, Reed-Solomon-koder, McElieces kryptosystem, Kryptering, Kodforcering, Komplexitetsteori, NP-fullständigt This work is produced on bachelor level in mathematics at University of Växjö. It is a study of coding theory with focus on cyclic codes in general and Reed-Solomon codes in detail. Reed-Solomon codes are used for implementing McEliece's crypto system. A short analysis of McEliece's crypto system security is also made together with a description of some known ways to break this type of cryptosystem. It is shown that using Reed-Solomon codes weaken this cryptosystem compared to using the original supposed Goppa codes. The security analyse also need a short summary of complexity theory and what it means that a problem is NP-complete. Keywords: Coding theory, Cyclic codes, BCH codes, Reed-Solomon codes, McEliece's cryptography system, Cryptography, Code breaking, Complexity theory, NP-complete

It is demonstrated that some problems can be solved inexpensively using widely distributed computers instead of an expensive supercomputer. This is illustrated by discussing how to make a simple fault-tolerant exhaustive code-breaking machine. The solution, which uses distributed processors is based on some elementary concepts of probability theory (lotto). The need for communication between processors is almost nil. Two approaches-deterministic and random-are compared. How to hide such a machine and how to build larger versions are discussed. >

1. Girolamo Cardano, De Subtilitate libri XXI, 1550. 2. Whitfield Diffie and Martin E. Hellman, New Directions in Cryptography, IEEE Transactions on Information Theory, Vol. IT-22 (November 1976), pp. 29-40. 3. Martin Gardner, Codes, Ciphers and Secret Writing, Dover Publications, Inc., New York, 1972. 4. Charlie Kaufman, Radia Perlman, and Mike Speciner, Network Security: PRIVATE Communication in a PUBLIC World, Prentice Hall, 1995. 5. Rudolf Kippenhahn, Code Breaking: A History and Exploration (English version translated from German), Overlook Press, Woodstock, N.Y., 1999. 6. National Institute of Standards and Technology (NIST), Digital Signal Standard, Federal Information Processing Standards (FIPS) Publication 186-2, 2000. 7. Bruce Schneier, Applied Cryptography (2nd Edition), John Wiley & Sons, Inc., 1996. 8. Simon Singh, The Code Book, Doubleday, 1999.