The bifid cipher, a bipartite cipher, is a combination of a substitution cipher and a transposition cipher.
It was invented by Felix Delastelle. Delastelle was a French who invented several ciphers, including two, three and four square ciphers. The first presentation of the bifid appeared in the French Revue du Génie civil in 1895 under the name cryptographie nouvelle.
The Bifid cipher is considered more secure as it breaks the message into two separate streams and then reconnects them. It uses a table omitting one letter of the alphabet. Often the letter J is removed and replaced with the letter I.
The basic element of the bifid cipher is the classic Polibius chessboard. However, while encryption with its help consists in simply replacing letters with two-digit numbers - coordinates of the table cells in which these letters are located, bifid adds the next stage to it - switching.
For example, we want to encode the word CALCOOLATOR . We look for each letter in the table and assign it a column number and a row number.
letters: C A L C O O L A T O R
row: 1 1 3 1 3 3 3 1 4 3 4
column: 3 1 1 3 4 4 1 1 4 4 2
Put the numbers in pairs by reading the row first, then the column. Then, in the table, we search for letters that our pairs of digits will indicate in the order row, column.
pairs: 11 31 33 31 43 43 11 34 41 14 42
row: 1 3 3 3 4 4 1 3 4 1 4
column: 1 1 3 1 3 3 1 4 1 4 2
letters: A L N L S S A O Q D R
So the scrambled word CALCOOLATOR would beALNLSSAOQDR.
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