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The Playfair cipher or Playfair square or Wheatstone–Playfair cipher is a manual symmetric encryption technique and was the first literal digram substitution cipher. The scheme was invented in 1854 by Charles Wheatstone , but bears the name of Lord Playfair for promoting its use.
The Two-square cipher, also called double Playfair, is a manual symmetric encryption technique. [1] It was developed to ease the cumbersome nature of the large encryption/decryption matrix used in the four-square cipher while still being slightly stronger than the single-square Playfair cipher .
In this cipher, a 5 x 5 grid is filled with the letters of a mixed alphabet (two letters, usually I and J, are combined). A digraphic substitution is then simulated by taking pairs of letters as two corners of a rectangle, and using the other two corners as the ciphertext (see the Playfair cipher main article for a diagram). Special rules ...
The Polybius square is also used as a basic cipher called the Polybius cipher. This cipher is quite insecure by modern standards, as it is a substitution cipher with characters being substituted for pairs of digits, which is easily broken through frequency analysis .
Then divided up into pairs again, and the pairs turned back into letters using the square: 44 33 35 32 43 13 55 31 23 25 U A E O L W R I N S In this way, each ciphertext character depends on two plaintext characters, so the bifid is a digraphic cipher, like the Playfair cipher. To decrypt, the procedure is simply reversed.
The four-square cipher is a manual symmetric encryption technique. [1] It was invented by the French cryptographer Felix Delastelle.. The technique encrypts pairs of letters (digraphs), and falls into a category of ciphers known as polygraphic substitution ciphers.
Delastelle's other polygraphic substitution ciphers included the trifid [3] and four-square ciphers. [4] The last of these is a variant on the earlier Playfair cipher: Delastelle may have been unaware of Playfair, but he had certainly read of the fractionating cipher described by Pliny Chase in 1859. There are few biographical details.
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