Cryptography Unit 
Cryptography, the use of codes and ciphers to protect secrets, began thousands of years ago. Until recent decades, it consisted of methods of encryption that used pencil and paper.  In the early 20th century, the invention of complex mechanical and electromechanical machines provided more sophisticated and efficient means of encryption.
 
By World War II, mechanical and electromechanical cipher machines were in wide use.  The Germans made heavy use, in several variations, of an electromechanical rotor machine known as Enigma
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The Enigma Machine used by Nazi Germany during WWII.
Marian Adam Rejewski was the first Polish mathematician and cryptologist who reconstructed the Nazi German military Enigma cipher machine sight-unseen in 1932.  The cryptologic achievements of Rejewski and his colleagues enabled the British to begin reading German Enigma-encrypted messages at the start of World War II.
 
However, by 1939, Enigma decryption had become dominated by the British and Americans.  The Polish mathematicians who had laid the foundation for Enigma decryption were now excluded from making further contributions in this area.  In due course, the British cryptographers at Bletchley Park – whose ranks included many chess masters and mathematicians such as Gordon Welchman, Max Newman and Alan Turing (the conceptual founder of modern computing) – substantially advanced the scale and technology of Enigma decryption.
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Marian Adam Rejewski (1905 - 1980)
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Alan Mathison Turing (1912 - 1954)
Lecture Notes & Other Resources