About

The Caesar Cipher is one of the oldest and simplest forms of encryption. It operates as a substitution cipher where each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a shift of 3, A would be replaced by D. The specific case of ROT13 uses a shift of 13, which is unique because it is its own inverse. Applying ROT13 to an already encrypted string restores the original text.

Accuracy in rotation ciphers depends on maintaining the case sensitivity and preserving non-alphabetic characters such as punctuation and whitespace. While ROT13 provides no real security against modern cryptanalysis, it remains a standard for obscuring spoilers in online forums or solving geocaching puzzles. This tool implements the full 26-character alphabet rotation using modular arithmetic to ensure precision across all n-shift variations.

Formulas

The encryption function E for a letter x with a shift n is defined by the modular congruence:

E(x) = (x + n) mod 26

To decrypt a letter y, the transformation is:

D(y) = (y − n) mod 26

Where:

x is the position of the character in the alphabet (0 to 25).
n is the rotation offset or key.
The result is wrapped using the modulo operator to ensure it remains within alphabet bounds.

Reference Data

Shift (n)	Name/Usage	A Maps To	M Maps To
1	Caesar (Standard)	B	N
5	Used in some puzzles	F	R
7	Common geocache variant	H	T
10	Decimal Shift	K	W
13	ROT13 (Standard)	N	Z
18	ROT5 + ROT13 mix	S	E
23	Reverse Shift (n-3)	X	J
25	Reverse Caesar	Z	L

Frequently Asked Questions

Standard ROT13 only affects the 26 letters of the Latin alphabet. Numbers, symbols, and spaces remain unchanged. This tool strictly follows that protocol to ensure maximum compatibility with existing geocaching and puzzle standards.

Absolutely not. ROT13 is a "weak" cipher that can be broken instantly via frequency analysis or brute force. It is intended for obfuscation (hiding spoilers) rather than true cryptographic security.

Because the English alphabet has 26 letters, shifting a letter by 13 and then by 13 again equals a shift of 26. Since 26 mod 26 is 0, the operation is symmetric. Shifting twice returns you to the original text.

If you find a cipher but don't know the shift key, Brute Force displays all 25 possible rotations at once. You can scan the results to see which one produces readable English text.