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144 BCE
Julius Caesar
Used a simple substitution with the normal alphabet (just shifting the letters a fixed amount) in government communications. He also used transliteration of Latin into Greek letters and a number of other simple ciphers. When Julius Caesar sent messages to his trusted acquaintances, he didn't trust the messengers. So he replaced every A by a D, every B by an E, and so on through the alphabet. Only someone who knew the ``shift by 3'' rule could decipher his message. -
Mar 31, 1379
Gabrieli di Lavinde
Compiled a combination substitution alphabet and small code. This class of code/cipher was to remain in general use among diplomats and some civilians for the next 450 years, in spite of the fact that there were stronger ciphers being invented in the meantime, possibly because of its relative convenience. -
Mar 31, 1466
Leon Battista Alberti
Invented and published the first polyalphabetic cipher, designing a cipher disk (known to us as the Captain Midnight Decoder Badge) to simplify the process. This class of cipher was apparently not broken until the 1800's. -
Mar 31, 1518
Johannes Trithemius
Wrote the first printed book on cryptology. He invented a steganographic cipher in which each letter was represented as a word taken from a succession of columns. The resulting series of words would be a legitimate prayer. -
Mar 31, 1553
Giovan Batista Belaso
Introduced the notion of using a passphrase as the key for a repeated polyalphabetic cipher. -
Blaise de Vigenère
Wrote a book on ciphers, including the first authentic plaintext and ciphertext autokey systems (in which previous plaintext or ciphertext letters are used for the current letter's key). -
Sir Francis Bacon
Described a cipher which now bears his name -- a biliteral cipher, known today as a 5-bit binary encoding. He advanced it as a steganographic device -- by using variation in type face to carry each bit of the encoding. -
Thomas Jefferson
Possibly aided by Dr. Robert Patterson (a mathematician at U. Penn.), invented his wheel cipher. -
Playfair Cipher
This cipher was actually invented by British scientist Sir Charles Wheatstone in 1854, but it bears the name of his friend Baron Playfair of St. Andrews, who championed the cipher at the British foreign office. The Playfair algorithm is based on the use of a 5 × 5 matrix of letters constructed using a keyword. -
Vernam Cipher
Developed techniques in cryptanalysis to choose a keyword that is as long as the plaintext and has no statistical relationship to it. Such a system was introduced by an AT&T engineer named Gilbert Vernam -
Hill Cipher
Multi-letter cipher developed by the mathematician Lester Hill -
Enigma
Was not a commercial success but it was taken over and improved upon to become the cryptographic workhorse of Nazi Germany. It was broken by the Polish mathematician, Marian Rejewski, based only on captured ciphertext and one list of three months worth of daily keys obtained through a spy. -
DES
A design by IBM based on the Lucifer cipher and with changes (including both S-box improvements and reduction of key size) by the US NSA, was chosen to be the U.S. Data Encryption Standard. It has since found worldwide acceptance, largely because it has shown itself strong against 20 years of attacks. -
New Directions in Cryptography
Whitfield Diffie and Martin Hellman introduced the idea of public key cryptography. -
RSA algorithm
Ronald L. Rivest, Adi Shamir and Leonard M. Adleman - It was a practical public-key cipher for both confidentiality and digital signatures, based on the difficulty of factoring large numbers. -
International Data Encryption Algorithm (IDEA)
Xuejia Lai and James Massey in Switzerland published ``A Proposal for a New Block Encryption Standard'', to replace DES. IDEA uses a 128-bit key and employs operations which are convenient for general purpose computers, therefore making software implementations more efficient. -
Phil Zimmermann
Released his first version of PGP (Pretty Good Privacy) in response to the threat by the FBI to demand access to the cleartext of the communications of citizens.