Nicolas Tadeusz Courtois is a cryptographer, a senior lecturer in computer science at University College London

University College London

University College London is a public research university located in London, United Kingdom and the oldest and largest constituent college of the federal University of London...

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Courtois was one of the co-authors of both the XSL attack

XSL attack

In cryptography, the XSL attack is a method of cryptanalysis for block ciphers. The attack was first published in 2002 by researchers Nicolas Courtois and Josef Pieprzyk. It has caused some controversy as it was claimed to have the potential to break the Advanced Encryption Standard cipher—also...

 against block cipher

Block cipher

In cryptography, a block cipher is a symmetric key cipher operating on fixed-length groups of bits, called blocks, with an unvarying transformation. A block cipher encryption algorithm might take a 128-bit block of plaintext as input, and output a corresponding 128-bit block of ciphertext...

s such as the Advanced Encryption Standard

Advanced Encryption Standard

Advanced Encryption Standard is a specification for the encryption of electronic data. It has been adopted by the U.S. government and is now used worldwide. It supersedes DES...

 and the XL system for solving systems of algebraic equations, used in the attack. Other cryptographic results of Courtois include algebraic attacks on 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...

s, attacks on the KeeLoq

KeeLoq

KeeLoq is a proprietary hardware-dedicated NLFSR-based block cipher. The uni-directional command transfer protocol was designed by Frederick Bruwer, PhD, CEO at Nanoteq Ltd and the cryptographic algorithm was created by Professor Gideon Kuhn with the silicon implementation by Willem Smit, PhD, at...

 and Hitag 2 systems used for remote keyless automobile entry systems

Remote keyless system

A remote keyless system is a system designed to permit or deny access to premises or automobiles. While the "remote" system is portable and has locking capabilities, the exact phrase "keyless entry" is solely reserved for the numeric dials or keypads that are located on or near the driver side door...

, and an analysis of cryptographic weaknesses in public transit smart card

Smart card

A smart card, chip card, or integrated circuit card , is any pocket-sized card with embedded integrated circuits. A smart card or microprocessor cards contain volatile memory and microprocessor components. The card is made of plastic, generally polyvinyl chloride, but sometimes acrylonitrile...

s including the London Underground

London Underground

The London Underground is a rapid transit system serving a large part of Greater London and some parts of Buckinghamshire, Hertfordshire and Essex in England...

 Oyster card

Oyster card

The Oyster card is a form of electronic ticketing used on public transport services within the Greater London area of the United Kingdom. It is promoted by Transport for London and is valid on a number of different travel systems across London including London Underground, buses, the Docklands...

 and the Dutch

Netherlands

The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

 OV-chipkaart

OV-chipkaart

The OV-chipkaart is a contactless smart card system which is in the process of being introduced on all public transport in the Netherlands, including train, metro, tram and bus...

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Courtois graduated from University of Paris VI: Pierre et Marie Curie

University of Paris

The University of Paris was a university located in Paris, France and one of the earliest to be established in Europe. It was founded in the mid 12th century, and officially recognized as a university probably between 1160 and 1250...

, where he got his doctoral degree in cryptography.