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Block Ciphers
Published in Alfred J. Menezes, Paul C. van Oorschot, Scott A. Vanstone, Handbook of Applied Cryptography, 2018
Alfred J. Menezes, Paul C. van Oorschot, Scott A. Vanstone
The Playfair cipher (Example 7.51), popularized by L. Playfair in England circa 1854 and invented by the British scientist C. Wheatstone, was used as a British field cipher [648, p.6]. J. Mauborgne (see also the Vernam and PURPLE ciphers below) is credited in 1914 with the first known solution of this digram cipher.
Hybrid lightweight cryptography with attribute-based encryption standard for secure and scalable IoT system
Published in Connection Science, 2022
Mounika Jammula, Venkata Mani Vakamulla, Sai Krishna Kondoju
The Playfair cypher is a multi-alphabet letter encryption cypher that treats plaintext letters as separate units and converts them to ciphertext letters. The Playfair cipher was the first effective digraph substitution cipher. A cipher that uses a digraphic substitution from a single alphabet square that starts with the letters of a keyword and continues with the letters of the remaining alphabet, excluding J. In contrast to standard ciphers, we encrypt a pair of alphabets (digraphs) rather than a single alphabet in playfair cipher. The Playfair cypher utilises Polybius Square for performing the encryption operation, which acts as a key. Alphabet characters are placed in a square matrix for the Polybius square cypher. The row x column concept is used to protect the message by replacing every character with a two-digit integer (every of varies from 1 to 5 owing to the alphanumeric characters being put in a 5 × 5 grid). In the polybius square, the alphabets should not be repeated and the matrix size is 5 × 5 with 25 elements. Further, the polybius square does not contain the letter J, which causes overlapping of bits in plain text. Therefore, if the letter “J” is present in the keystream, then it is replaced with the letter “I”. In addition, the letters in the polybius square should not be repeated. Then, the encryption process is performed as follows: