ROT-13 Cipher

Encryption with Rot-13 replaces a letter by another one placed 13 ranks after in the alphabet. Each letter is therefore shifted by 13 positions in the English alphabet. The correspondance table is:

Example: DCODE is crypted QPBQR with ROT-13

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

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

Example: URYYB becomes HELLO.

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

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 a method of spoil.

Rot-13 is in fact a Caesar cipher with a shift of 13. As this code only works with letters, it was proposed to use it with the Rot5 for numbers or the Rot47 for ASCII values.

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.