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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 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 . ROT13 can be referred by "Rotate13", "rotate by 13 places", hyphenated "ROT-13" or sometimes by its autonym "EBG13".
The following attack on the Caesar cipher allows full recovery of the secret key: Suppose the adversary sends the message: Attack at dawn, and the oracle returns Nggnpx ng qnja. The adversary can then work through to recover the key in the same way as a Caesar cipher. The adversary could deduce the substitutions A → N, T → G and so on. This ...
All polyalphabetic ciphers based on the Caesar cipher can be described in terms of the tabula recta. The tabula recta uses a letter square with the 26 letters of the alphabet followed by 26 rows of additional letters, each shifted once to the left from the one above it. This, in essence, creates 26 different Caesar ciphers. [1]
A well-known example of a substitution cipher is the Caesar cipher. To encrypt a message with the Caesar cipher, each letter of message is replaced by the letter three positions later in the alphabet. Hence, A is replaced by D, B by E, C by F, etc. Finally, X, Y and Z are replaced by A, B and C respectively.
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.
Classical ciphers are typically vulnerable to known-plaintext attack. For example, a Caesar cipher can be solved using a single letter of corresponding plaintext and ciphertext to decrypt entirely. A general monoalphabetic substitution cipher needs several character pairs and some guessing if there are fewer than 26 distinct pairs.
The cipher family was chosen as a finalist of the CAESAR Competition [3] in February 2019. NIST had announced its decision on February 7, 2023 [3] with the following intermediate steps that would lead to the eventual standardization: [2] Publication of NIST IR 8454 describing the process of evaluation and selection that was used;