
Baconian Cipher
To encode a message, each letter of the plaintext is replaced by a group of five of the letters 'A' or 'B'. This replacement is done according to the alphabet of the Baconian cipher, shown below. a AAAAA g AABBA m ABABB s BAAAB y BABBA b AAAAB h AABBB n ABBAA t BAABA z BABBB c AAABA i ABAAA o ABBAB u BAABB d AAABB j BBBAA p ABBBA v BBBAB e AABAA k ABAAB q ABBBB w BABAA f AABAB l ABABA r BAAAA x BABAB
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Affine Cipher
In the affine cipher the letters of an alphabet of size m are first mapped to the integers in the range 0..m  1. It then uses modular arithmetic to transform the integer that each plaintext letter corresponds to into another integer that correspond to a ciphertext letter. The encryption function for a single letter is where modulus m is the size of the alphabet and a and b are the key of the cipher. The value a must be chosen such that a and m are coprime. Considering the specific case of encrypting messages in English (i.e. m = 26), there are a total of 286 nontrivial affine ciphers, not counting the 26 trivial Caesar ciphers. This number comes from the fact there are 12 numbers that are coprime with 26 that are less than 26 (these are the possible values of a). Each value of a can have 26 different addition shifts (the b value) ; therefore, there are 12*26 or 312 possible keys. Plaintext: nests
The decryption function is where a  1 is the modular multiplicative inverse of a modulo m. I.e., it satisfies the equation The multiplicative inverse of a only exists if a and m are coprime. Hence without the restriction on a decryption might not be possible. It can be shown as follows that decryption function is the inverse of the encryption function, Read more ... 
ROT13 Cipher
Applying ROT13 to a piece of text merely requires examining its alphabetic characters and replacing each one by the letter 13 places further along in the alphabet, wrapping back to the beginning if necessary. A becomes N, B becomes O, and so on up to M, which becomes Z, then the sequence continues at the beginning of the alphabet: N becomes A, O becomes B, and so on to Z, which becomes M. Only those letters which occur in the English alphabet are affected; numbers, symbols, whitespace, and all other characters are left unchanged. Because there are 26 letters in the English alphabet and 26 = 2 * 13, the ROT13 function is its own inverse: ROT13(ROT13(x)) = x for any basic Latinalphabet text x An example plaintext to ciphertext using ROT13:
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Polybius Square
A Polybius Square is a table that allows someone to translate letters into numbers. To give a small level of encryption, this table can be randomized and shared with the recipient. In order to fit the 26 letters of the alphabet into the 25 spots created by the table, the letters i and j are usually combined.
Basic Form:
Extended Methods: Method #1 Plaintext: nests
Method #2 Bifid cipher The message is converted to its coordinates in the usual manner, but they are written vertically beneath: n e s t s 3 5 3 4 3 3 1 4 4 4They are then read out in rows: 3534331444 Then divided up into pairs again, and the pairs turned back into letters using the square:
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Permutation Cipher
In classical cryptography, a permutation cipher is a transposition cipher in which the key is a permutation. To apply a cipher, a random permutation of size E is generated (the larger the value of E the more secure the cipher). The plaintext is then broken into segments of size E and the letters within that segment are permuted according to this key. In theory, any transposition cipher can be viewed as a permutation cipher where E is equal to the length of the plaintext; this is too cumbersome a generalisation to use in actual practice, however. The idea behind a permutation cipher is to keep the plaintext characters unchanged, butalter their positions by rearrangement using a permutation This cipher is defined as: Let m be a positive integer, and K consist of all permutations of {1,...,m} For a key (permutation) , define: The encryption function The decryption function A small example, assuming m = 6, and the key is the permutation : The first row is the value of i, and the second row is the corresponding value of (i) The inverse permutation, is constructed by interchanging the two rows, andrearranging the columns so that the first row is in increasing order, Therefore, is: Total variation formula: e = 2,718281828 , n  plaintext length Plaintext: nests
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