Caesar Cipher Encoder and Decoder
The Caesar cipher replaces every letter with the one a fixed number of places further along the alphabet. Type your text and choose the shift to get the result instantly. If you do not know the shift, the solver tries all 25 possibilities and marks the most likely one.
Source: Wikipedia – Caesar cipher (Verfahren, ROT13, Brechen per Häufigkeitsanalyse). Updated: .
How it is calculated
The Caesar cipher is a shift cipher: every letter moves the same number of places along the alphabet. With a shift of 3, A becomes D, B becomes E, and at the end of the alphabet it wraps around, so X becomes A. “VENI” turns into “YHQL”. The Roman historian Suetonius reports that Julius Caesar protected his letters this way.
How the tool works
- Encode: enter your text and a shift. The mapping shows which letter is replaced by which.
- Decode with a key: the text is shifted back by the same number.
- Solve without a key: there are only 25 useful shifts, so trying them all is easy. The table lists every result, and a star marks the most likely one, found by comparing letter frequencies – in English, E is the most common letter at roughly 12.7 percent.
- Accents: the classic alphabet has only A to Z. By default the tool therefore converts letters like é or ü first; switch that off to leave them untouched.
ROT13 and the limits of the method
A shift of 13 makes encoding and decoding the same step, because the alphabet has 26 letters. ROT13 is used online to hide spoilers. As protection the Caesar cipher is worthless today: with only 25 keys it falls in seconds, and the letter frequencies survive the shift. For real secrecy use modern encryption, and for a strong password try the password generator. For puzzles and lessons, the Morse code translator and text to binary converter make good companions.
Frequently asked questions
How does the Caesar cipher work?
Each letter is moved a fixed number of places along the alphabet. With a shift of 3, “HELLO” becomes “KHOOR”. To decode, you shift back by the same number.
How do you break a Caesar cipher without the key?
There are only 25 possible shifts, so you can try them all. A faster way is frequency analysis: the most common letter in the ciphertext is usually the shifted E.
What is ROT13?
ROT13 is the Caesar cipher with a shift of 13. Since 13 is half of the 26-letter alphabet, the same operation both encodes and decodes.
What happens to numbers, spaces and punctuation?
Spaces and punctuation are left unchanged. Digits are only shifted if you switch that option on. Accented letters can be converted to plain A–Z first.
Is the Caesar cipher secure?
No. It is a historical method that can be broken with almost no effort. Use it for puzzles, teaching and games, never for confidential data.
Sources and legal basis
- Wikipedia – Caesar cipher (Verfahren, ROT13, Brechen per Häufigkeitsanalyse)
- Wikipedia – Letter frequency (letter frequencies by language, basis of the estimate)
As of: · Editorial policy
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