ROT Cipher

Reference

What is a ROT cipher?

A ROT cipher (rotation cipher) is a simple letter substitution cipher that shifts each letter by a fixed number of positions in the alphabet. ROT13 is the most well-known variant — it shifts letters by 13 positions, making it self-reciprocal: encoding and decoding use the same operation. ROT ciphers are a specific case of the Caesar cipher, one of the oldest encryption techniques attributed to Julius Caesar.

ROT cipher variants

ROT1 — shifts letters by 1 (A→B, B→C). The simplest rotation. ROT5 — rotates digits only (0→5, 1→6, …, 5→0). Leaves letters unchanged. ROT13 — shifts letters by 13. Self-reciprocal: applying it twice returns the original text. The most commonly used variant. ROT18 — combines ROT13 (letters) + ROT5 (digits). Both letters and numbers are rotated. ROT47 — rotates all printable ASCII characters (! through ~) by 47 positions. Covers letters, digits, and symbols. Also self-reciprocal. Custom — any shift from 1 to 25 for letters.

Common use cases

Spoiler hiding — ROT13 is traditionally used to hide spoilers in forums and newsgroups. Obfuscation — lightly obscure text like email addresses from simple scrapers. Puzzles & games — create or solve simple substitution cipher challenges. Education — learn about classical cryptography and substitution ciphers. CTF challenges — ROT ciphers frequently appear in capture-the-flag competitions.

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