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100 BCE
Caesar Cipher
The Caesar Cipher, also known as a substitution cipher is a method of substituting letters for different letters, and only those with knowledge of the substitution used could decipher the message.
It is one of the earliest methods of secure communication recorded for military use. As commander of the Roman Army, Julius Caesar used this method for secure communications with his troops by substituting each letter with a letter three positions forward. -
1361
Subh al-a 'sha
A list of ciphers written by Ahmad al-Qalqashandi as part of a 14-voulme encyclopedia. This list consisted of substitution and transposition methods, as well as marking the first instance of a cipher with multiple substitutions for each plaintext letter. -
1467
Alberti-Vigenère Cipher
The Alberti-Vigenère Cipher is based on a variation of the Caesar Cipher where a series of different Caeser Ciphers are applied on a plaintext, based on the letters of a keyword. The keyword determines the number of shifts. This polyalphabetic cipher was first well-documented around 1467 by Leon Battista Alberti, reinvented by Giovan Battista Bellaso in the 16th century, and misattributed to Blaise de Vigenère in the 19th century. It would be used later in the American Civil War. -
Babington Plot
Sir Francis Walsingham used cryptanalysis to expose a plot to murder Queen Elizabeth I of England by the Queen of Scots, Mary. -
Wheel Cipher
The Wheel Cipher was invented by Thomas Jefferson while serving as George Washington's secretary of state, which he began working on when he was America's minister to France. The wheel consisted of thirty-six cylindrical wooden pieces inscribed with the letters of the alphabet threaded onto an iron spindle in a random order. This method prevented Jefferson's communications with Washington from being read by the European postmasters. -
The Kasiski Test
Charles Babbage developed a method to analyze and statistically decrypt messages that had been encrypted by the Vigenere square in 1854. However, due to his lack of organization, his papers were often incomplete. As a result, the honor would go to Friedrich Kasiski who developed and documented the same statistical method to crack Vigenere in 1863. The technique was later named the "Kasiski Test". -
Kerckhoffs's principle
It is a list of six design principles written by Auguste Kerckhoffs in the French publication La Cryptographie Militaire. Kerckhoffs believes that even if everything about a system is not secured, including the key, its cryptosystem must completely be. This approach is very popular with modern-day cryptographers. -
The Dreyfus affair
Cryptography played a major part in convicting French Army Captain Alfred Dreyfus of treason, which marked the beginning of the scandal. Dreyfus was accused of sharing secret government files to a foreign government after a shredded letter was discovered at the German Embassy in Paris. -
The Zimmerman Telegram
British cryptographers deciphered a telegram from the German Foreign Secretary, Arthur Zimmerman, to the German ambassador in Mexico, Heinrich von Eckart, and changed the history of cryptanalysis. The telegram detailed Germany's plan to broke the Sussex pledge, which limited submarine warfare, as well as proposing military and financial support for Mexico to attack the US and reclaim Arizona, New Mexico, and Texas. The US declared war on Germany once presented with the telegram. -
Vernam Cipher
It is a polyalphabetic stream cipher, which would later be used to invent the one-time pad. Developed by Gilbert Sanford Vernam, the cipher calls for a prepared key that is kept on paper tape to be combined with characters of the plaintext message to produce the ciphertext. Cryptographers have called this approach one of the most important in cryptography history. -
Choctaw Code talkers
Due to constant interceptions of American military's communications by the German in WWI, the US decided to encrypt its communications by using American Indian soldiers to communicate movements in their native and unique languages. This accidental discovery gave the Americans a huge advantage and was a major turning point of the war. -
M-94/CSP-488
Re-inventing Thomas Jefferson's Wheel Cipher, the US Army began developing a similar method of cryptography in 1917 and officially adopted it in 1922. Instead of Jefferson's 36 wooden wheels, the Army's version consisted of 24. The US military utilized the M-94(Army)/CSP-488(Navy) at the beginning of WWI and remained until 1945. -
Enigma Machines
The Enigma machine is a series of electro-mechanical cipher machine used heavily and overconfidently by the German military during WWII because of its seemingly endless possible configurations. It was virtually unbreakable with brute force methods. It was eventually compromised by the Allied forces mainly because of human errors by its operators and weakness in its substitution algorithm. -
M-209/CSP-1500/C-38
This cipher machine is an improvement on the earlier machine, the C-36. The C-38 is a lunchbox size portable cipher machine developed by the Swedish cryptographer Boris Hagelin in 1944, which consisted of six adjustable key wheels, each displaying a letter of the alphabet. The key wheels advance one letter after each enciphered message. A ciphertext that is printed on a paper tape at the end of an encipher cycle were then commonly transmitted via Morse code. -
Information Theory and Entropy
Information Theory was proposed by Claude E. Shannon in a paper titled "A Mathematical Theory of Communication". He sought to identify the fundamental limits of signal processing and communications. This theory is widely used in cryptography among other fields in the form of "Entropy", which helps put a value on a number of possibilities present in a random process or variable, such as a coin flip, or a roll of a die. Low entropy(two) on the coin. Six equal outcomes on the die. -
Gulf of Tonkin Incident
Misinterpretation of signals by the NSA led the US deeper into conflict with North Vietnam. Because of the previous confrontation between a US navy vessel and one from the North Vietnamese two days earlier where the two exchanged fire, a false reading of radar images, which was later discovered to be so was to blame for the August 4 incident that triggered the United States' response to engage deeper in the conflict. -
Data Encryption Standard (DES)
DES is an improvement based on IBM and Horst Feistel's designs, selected by the National Bureau of Standards (NBS) in consultation with the NSA in establishing a standard method of protecting sensitive and unclassified government electronic data. This was as a result of the US government widespread use of new commercial systems. It would later be replaced because of its weakness against brute force attacks. Its 56-bit key size is too small for modern computing, therefore deemed unsecured. -
Exportation of Cryptography
The US government announced the relaxation of restrictions on the export of cryptography. Though the move was not a complete reversal of previous policies, it helped alleviate some burden on US software makers on having to create different copies for US and International markets. -
Advanced Encryption Standard (AES)
Established by the National Institute of Standards and Technology (NIST) after requesting proposals from cryptographers. Vincent Rijmen and Joan Daemen developed the family of ciphers with various key and block sizes, also known as the Rijndael Cipher, which would later be selected by the NIST and renamed the AES. This cipher is now considered the standard worldwide (ISO/IEC 18033-3) since being adopted and deployed for use on US government systems.
