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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 .
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.
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.
An early substitution cipher was the Caesar cipher, in which each letter in the plaintext was replaced by a letter three positions further down the alphabet. [23] Suetonius reports that Julius Caesar used it with a shift of three to communicate with his generals. Atbash is an example of an early Hebrew cipher.
As depicted, the Caesar cipher uses a substitution method much like the Aristocrat, however, instead of inserting a keyword into the ciphertext, you shift the ciphertext by three to the left. Coined in 1929 by a group of friends, a part of the American Cryptogram Association (ACA), the Aristocrat Cipher's name was a play on words intended to ...
The remaining two rows are labeled with one of the two digits that were not assigned a letter in the second row, and then filled out with the rest of the alphabet, plus the two symbols '.' and '/'. The period '.' is used as a full stop or decimal separator ,
The cipher alphabet on the second row uses B for A and C for B etc. That is cipher alphabet 'B'. Each cipher alphabet is named by the first letter in it. For example, if the keyword is LEMON and the message to encode is ATTACKATDAWN, then the encoding is: