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In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code, or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet .
ROT13 is a simple letter substitution cipher that replaces a letter with the 13th letter after it in the Latin alphabet. ROT13 is a special case of the Caesar cipher which was developed in ancient Rome, used by Julius Caesar in the 1st century BC. [1] An early entry on the Timeline of cryptography.
The Caesar cipher is an Affine cipher with a = 1 since the encrypting function simply reduces to a linear shift. The Atbash cipher uses a = −1 . Considering the specific case of encrypting messages in English (i.e. m = 26 ), there are a total of 286 non-trivial affine ciphers, not counting the 26 trivial Caesar ciphers.
ROT13 is a Caesar cipher, a type of substitution cipher.In ROT13, the alphabet is rotated 13 steps. Substitution of single letters separately—simple substitution—can be demonstrated by writing out the alphabet in some order to represent the substitution.
The ciphertext alphabet is rearranged according to a keyword, which then replaces the plaintext letters. K3 Cipher: This variation uses both a keyed plaintext and a keyed ciphertext alphabet, but the same keyword is used for both. K4 Cipher: Similar to the K3 Cipher, but different keywords are used for the plaintext and ciphertext alphabets.
in which c is the size of the alphabet (26 for English), N is the length of the text and n 1 to n c are the observed ciphertext letter frequencies, as integers. That is, however, only an approximation; its accuracy increases with the length of the text. It would, in practice, be necessary to try various key lengths that are close to the ...
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Now an alphabet of 32 characters can carry 5 bits of information per character (as 32 = 2 5). In general the number of bits of information per character is log 2 (N), where N is the number of characters in the alphabet and log 2 is the binary logarithm. So for English each character can convey log 2 (26) = 4.7 bits of information.