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Security: Basics and Security Analytics
Published in Rakesh M. Verma, David J. Marchette, Cybersecurity Analytics, 2019
Rakesh M. Verma, David J. Marchette
The two basic techniques for encryption are substitution and permutation. For example, the so-called Caesar Cipher is a substitution cipher in which every letter is encoded by the third letter after it, treating the English alphabet circularly, so that the letters, A, B, C, “follow” the letter Z. If we encode the 26 letters using numbers 0 to 25 with 0 representing letter A and 25 representing Z, then we can write that the ciphertext number Nc = Np + 3 mod 26 when the plaintext number is Np. Similarly the equation for decryption is straightforward. The Caesar Cipher is called a monoalphabeticencryption!monoalphabetic cipher since each letter is encoded by a single letter and the encoding is fixed. Polyalphabeticencryption!polyalphabetic cipher schemes may encode several letters together or use different letters as encodings of the same letter or both. Polyalphabetic ciphers use a set of related monoalphabetic ciphers. Examples of polyalphabetic ciphers are the Vignere cipher and the Vernam cipher in which the user selects a key, which is then repeated if it is shorter than the message. Each letter of the key is an index into a monoalphabeticencryption!monoalphabetic cipher and the substitution for the plaintext letter is done using the substitution rule of the chosen monoalphabetic cipher.
Deciphering the Hermeticae Philosophiae Medulla: Textual Cultures of Alchemical Secrecy
Published in Ambix, 2023
Megan Piorko, Sarah Lang, Richard Bean
In modern cryptological scholarship polyalphabetic substitution ciphers are known as Vigenère types after the sixteenth-century French cryptographer Blaise de Vigenère, who published this type of cipher in 1586. The polyalphabetic method of encryption was pioneered by Giovani Battista Bellaso in 1552, first published as a series of pamphlets between 1553–1564. Despite earlier publications by Bellaso, polyalphabetic substitution ciphers were not widely used until the mid-seventeenth century, when they were popularised as Della Porta ciphers following his 1563 publication De Furtivis, which illustrated the use of this type of cipher without crediting Bellaso. While Vigenère did acknowledge the work of Bellaso in his publication, Vigenère remains the cipher’s namesake today.30 Both Della Porta and Vigenère borrow from Bellaso the concept of employing a key word in combination with a cipher table (tabula recta or “Porta table”) to create a polyalphabetic cipher, which became characteristic of the “Vigenère type” of polyalphabetic ciphers thereafter. Della Porta also published alchemical treatises (such as De distillatione libri XI, 1608), which may have drawn alchemical practitioners to his previous publications on polyalphabetic encryption. Thus, the inclusion of Hermeticae Philosophiae Medulla cipher in Sloane MS 1902 is a relatively early and rare example of a Bellaso/Della Porta polyalphabetic type.31