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ROT-13 Cipher

Tool to decrypt/encrypt with rot13. ROT-13 cipher is a particular case of the Caesar cipher, where the shift is equal to 13, this allow the cipher to be reciprocal.

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ROT-13 Cipher -

Tag(s) : Substitution Cipher

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# ROT-13 Cipher

## ROT13 Encoder

### What is Rot-13? (Definition)

Rot-13 (short for Rotation 13) is the name given to a mono-alphabetical substitution cipher which has the property of being reversible and very simple.

Combining the French/Latin alphabet of 26 letters and an offset of 13, Rot-13 replaces a letter with another located 13 places further down the alphabet.

Rot-13 coding is popular because it is easily reversible, indeed, if it is applied twice, then the original message reappears.

This is a special case of the Caesar cipher (and more generally shift ciphers).

### How to encrypt using Rot-13?

From an alphabet, usually the classic 26-letter alphabet ABCDEFGHIJKLMNOPQRSTUVWXYZ, each letter is shifted by 13 positions in the English alphabet. The correspondence table is:

 ABCDEFGHIJKLMNOPQRSTUVWXYZ NOPQRSTUVWXYZABCDEFGHIJKLM

Example: DCODE is encrypted QPBQR with ROT-13

This is a special case of the Caesar cipher (and more generally shift ciphers)

### How to decrypt a Rot-13 cipher?

Rot-13 decryption is identical to encryption, due to the reciprocal substituting alphabet used:

 NOPQRSTUVWXYZABCDEFGHIJKLM ABCDEFGHIJKLMNOPQRSTUVWXYZ

Example: URYYB becomes HELLO.

Rot-13 has the same function for encryption and decryption, it is said to be involutive.

### How to recognize ROT-13 ciphertext?

Frequency analysis shows a shift of 13 letters (The E is replaced by an R, which should be the most present letter).

A message encoded by Rot13 has an index of coincidence similar to the language of the plain text.

The ROT13 code has been widely popularized on Usenet groups and discussion forums, for example as an anti-spoil method.

### What are the variants of the Rot-13 cipher?

Rot-13 is in fact a Caesar cipher with a shift of 13. As this code only works with letters, it is possible to add the Rot5 to it for the digits (in this case it is sometimes called ROT13.5) or even to use the Rot47 to manage all the ASCII characters.

### What is the particularity of the ROT13 Cipher?

An offset of 13 allows the encryption to be reversible. The encryption and decryption method are identical. Applying 2 consecutive encryptions (2 shifts of 13) heads to find the original text.

### Why does 2 encryption with ROT13 cancel each other?

Applying 2 shifts of 13 represents a shift of 26, and for the Latin alphabet of 26 letters, this amounts to shifting all the letters to their starting point, so in the end, not undergoing any transformation.

ROT13(ROT13(letter)) = letter

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