About Cipher Tools
Classical ciphers are letter-substitution schemes that predate computers. Caesar shifts each letter by a fixed number of places, ROT13 is a Caesar shift of 13, Atbash mirrors the alphabet (A becomes Z), and Vigenère shifts each letter by the matching letter of a repeating keyword. This tool changes only the letters A to Z and keeps case, digits, and punctuation. None of these ciphers is secure: all can be broken quickly by hand.
How to use Cipher Tools
- Type or paste into the "Input text" box, or press "Use example" to try it with sample data.
- Set "Cipher", "Shift" and "Direction" if the defaults do not fit.
- The result appears below and updates as you type.
- Copy the result with the copy button, or download it as a file where that is offered.
Questions about Cipher Tools
Why is ROT13 the same for encoding and decoding?
The alphabet has 26 letters, and ROT13 shifts by exactly half of it. Applying the shift twice moves each letter 26 places, back to where it started, so one operation does both jobs.
How is a Caesar cipher broken?
There are only 25 possible shifts, so trying each one takes seconds. Letter frequency also gives it away: the most common letter in the ciphertext usually stands for E in English text.
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