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CryptologyHISTORYEarly cryptographic systems and applications. |
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People have probably tried to conceal information in written form from the time that writing developed. Examples survive in stone inscriptions, cuneiform tablets, and papyruses showing that the ancient Egyptians, Hebrews, Babylonians, and Assyrians all devised protocryptographic systems both to deny information to the uninitiated and to enhance its significance when it was revealed. The first recorded use of cryptography for correspondence, however, was by the Spartans, who as early as 400 BC employed a cipher device called the scytale for secret communications between military commanders. The scytale consisted of a tapered baton, around which was spirally wrapped a strip of parchment or leather on which the message was written. When unwrapped, the letters were scrambled in order and formed the cipher; however, when the strip was wrapped around another baton of identical proportions to the original, the plaintext reappeared. Thus, the Greeks were the inventors of the first transposition cipher. During the 4th century BC Aeneas Tacticus wrote a work entitled On the Defense of Fortifications, one chapter of which was devoted to cryptography, making it the earliest treatise on the subject. Another Greek, Polybius, devised a means of encoding letters into pairs of symbols by a device called the Polybius checkerboard, which is a true biliteral substitution and presages many elements of later cryptographic systems. Similar examples of primitive substitution or transposition ciphers abound in the history of other civilizations. The Romans used monoalphabetic substitution with a simple cyclic displacement of the alphabet. Julius Caesar employed a shift of three positions so that plaintext A was encrypted as D, while Augustus Caesar used a shift of one position so that plaintext A was enciphered as B. |
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The first people to clearly understand the principles of cryptography and to elucidate the beginnings of cryptanalysis were the Arabs. They devised and used both substitution and transposition ciphers and discovered the use of both letter frequency distributions and probable plaintext in cryptanalysis. As a result, by about 1412, al-Kalka-shandi could include a respectable, if elementary, treatment of several cryptographic systems in his encyclopaedia Subh al-a'sha and give explicit instructions on how to cryptanalyze ciphertext using letter frequency counts complete with lengthy examples to illustrate the technique. |
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European cryptology dates from the Middle Ages, during which it was developed by the Papal States and the Italian city-states. The earliest ciphers involved only vowel substitution (leaving consonants unchanged). The first European manual on cryptography (c. 1379) was a compilation of ciphers by Gabriele de Lavinde of Parma, who served Pope Clement VII. This manual, now in the Vatican archives, contains a set of keys for 24 correspondents and embraces symbols for letters, nulls, and several two-character code equivalents for words and names. The first brief code vocabularies, called nomenclators, were gradually expanded and became the mainstay for several centuries for diplomatic communications of nearly all European governments. In 1470 Leon Battista Alberti published Trattati in cifra, in which he described the first cipher disk; he prescribed that the setting of the disk should be changed after enciphering three or four words, thus conceiving of the notion of polyalphabeticity. Giambattista della Porta provided a modified form of square table and the earliest example of a digraphic cipher in De furtivis literarum notis (1563). The Traicté des chiffres published in 1586 by Blaise de Vigenère contains the square table commonly attributed to him (Figure 2) and descriptions of the first plaintext and ciphertext autokey systems. |
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By 1860 large codes were in common use for diplomatic communications, and cipher systems had become a rarity for this application. Cipher systems prevailed, however, for military communications except for high-command communications because of the difficulty of protecting codebooks from capture or compromise in the field. In the early history of the United States, codes were widely used, as were book ciphers. During the Civil War the Federal Army made extensive use of transposition ciphers, in which a key word indicated the order in which columns of the array were to be read and in which the elements were either plaintext words or code word replacements for plaintext. The Confederate Army primarily used the Vigenère cipher and on occasion monoalphabetic substitution. While the Union cryptanalysts solved most of the intercepted Confederate ciphers, the Confederacy in desperation sometimes published Union ciphers in newspapers, appealing for help from readers in cryptanalyzing them. (see also Index: American Civil War) |
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To cite this page:
"Cryptology: HISTORY" Britannica Online. <http://www.eb.com:180/cgi-bin/g?DocF=macro/5001/60/14.html> [Accessed 15 February 1999]. |
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