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Ciphers, Codes and Encryption Technologies


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Public Key Cryptography Explained A basic metaphorical explanation of a specific type of authentication process commonly used in civilian cryptography. Also explains the basics of ‘Modular Arithmetic’, a fundamental tool of traditional cryptography.

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On Cryptography, Coding and Information Theory

The word ‘Cryptography’ is in fact Greek and denotes ‘Secret Writing’ in that language. Essentially, Cryptography is the means by which two parties may communicate without having their message understood by a third party. The three necessary components for a ‘Cryptogram’ – also called a ‘Cipher’ are Authentication (the handshake and verification of the message source), Data Integrity (the ability to convey the message with no loss to it’s meaning or content) and Confidentiality (preventing third party adversaries from being able to understand it).

Since the Industrial Revolution and especailly World War I the means by which Cryptography was done has become increasingly complex. The Lorenz cipher machine, or ‘Enigma’ as it was called, used by the German High Command, was the very first machine to employ switching technology as an integral part of it’s special linguistic mechanism, or encryption.

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lorenz cipher machine - or 'enigma' machine used by the nazis  

at left: The infamous German ‘Enigma’ machine


image courtesy of the BBC.

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In 1948 , a scientist working for Bell Laboratories in New Jersey named Claude Shannon wrote a paper called "A Mathematical Theory of Communication" for the Bell System Technical Journal. This paper built on his earlier interest in the Boolean (logical) analysis of electrical (in fact digital) signals studied in his thesis, titled An Algebra for Theoretical Genetics. By also substantially using the probability theory of mathematician Norbert Wiener, Shannon was able to exploring the intricacies of the best means of encoding information being sent electronically – not only for the purpose of secrecy and electrical efficacy – but this body of work also dealt with the problems of how to reconstruct messages due to lost information with no apparent loss of security to the sender. By adopting a special application of the concept of ‘entropy’, or ‘information entropy’.

By applying these tools – Shannon was able to establish mathematically, the level of security of (breakability) of various types and forms of encrypted messages and their ‘keys’ (a set of instructions for deciphering a given code). In his 1949 paper "Communication Theory of Secrecy Systems" Shannon devoted himself to a fuller mathematical study to the innate properties of digital cryptography. The results of this work had significant applications in many fields; Cryptography, Natural Language Processing, Data Compression and many others.

Years earlier, in 1940, Alan Turing (also known as the father of the logical machine and modern digital computer) worked with similar concepts as Shannon in the breaking of the German Enigma Machine cipher (or ‘code’). In this case, Turing was able to reverse engineer the actual structure of the German device based on it’s own electromechanical language of dials and switches, based on the logic of it’s transmissions. There was no currently existing theory or field of study which would have allowed for this insight – except for the mathematical work of Boltzmann and Gibbs, whose work on thermodynamics and predictive analyses – gave some insight into the problems faced by Turing.

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VIDEO: The Enigma Secret, 1998

In December 1932, the Polish Cipher Bureau first broke Germany’s Enigma ciphers.
Five weeks before the outbreak of World War II, on 25 July 1939, in Warsaw, the Polish Cipher Bureau gave Enigma-decryption techniques and equipment to French and British military intelligence. Thanks to this, during the war, Allied codebreakers were able to decrypt a vast number of messages that had been enciphered using the Enigma. The intelligence gleaned from this source, codenamed "Ultra" by the British, was a substantial aid to the Allied war effort.


LECTURE: The Science of Secrecy

Join Imperial’s Institute for Security Science and Technology for an informative presentation on codes, ciphers and computers. Professor Richard Aldrich, Dr Martin Knight, Professor Sir Peter Knight and Dr Simon Singh take you on a tour of cryptography through the ages. From its beginnings in pen and paper to its future in quantum computing.





VIDEO: Bletchley Park’s Lost Heroes

Documentary that reveals the secret story behind one of the greatest intellectual feats of World War II, a feat that gave birth to the digital age. In 1943, a 24-year-old maths student and a GPO engineer combined to hack into Hitler’s personal super-code machine – not Enigma but an even tougher system, which he called his ‘secrets writer’. Their break turned the Battle of Kursk, powered the D-day landings and orchestrated the end of the conflict in Europe. But it was also to be used during the Cold War – which meant both men’s achievements were hushed up and never officially recognised.

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The history of ARPA leading up to the ARPANET

Birth of the Internet: The Arpanet – General Overview

An Introduction to Information Theory: Symbols, Signals & Noise , John Robinson Pierce

Claude Shannon on Wikipedia

‘Information Theory, Wikipedia

Simon Mason’s Shortwave Espionage Page

Wikipedia’s article "Outline of the Internet"


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