Caesar Cipher

Caesar Cipher - How does it work?

The Caesar cipher is one of the oldest ciphers - each letter is replaced by a letter a fixed number of positions away in the alphabet (classically by 3). Our tool encrypts and decrypts text at any shift, and in addition to the Caesar cipher, it also supports related substitution ciphers.

Supported ciphers

• Caesar cipher – shift by selected number (key),
• ROT13 – shift by 13, symmetric (encrypt = decrypt),
• Atbash – reverse alphabet (A↔Z, B↔Y…),
• GA-DE-RY-PO-LU-KI – a popular scout cipher, replaces letters in pairs.

Encryption step by step - example

The principle is simple: replace each letter of the plaintext with a letter separated by a fixed number of positions (key) in the alphabet. With the classic shift by 3 (ROT3) in the Latin alphabet: A→D, B→E, C→F... and the letters from the end of the alphabet "wrap" to the beginning (X→A, Y→B, Z→C). The password ATTACK AT DAWN after reducing Polish characters to basic ones (Ś→S) gives the ciphertext DWDN R VZLFLH. Decryption is the same operation in the opposite direction - shifting back 3 positions.

History: Julius Caesar and Suetonius' account

The name of the cipher comes from Julius Caesar, who - as the Roman historian Suetonius writes in "Lives of the Caesars" - encrypted private correspondence by replacing each letter with a letter three positions apart. His successor, Octavian Augustus, used a simpler version with a shift of 1, and instead of the last letter of the alphabet he wrote a double A. At a time when most people could not read, this protection was completely sufficient - today the Caesar cipher is a classic cryptography for learning and fun, not for data protection.

Classical cipher family

ROT13

Caesar cipher with shift 13. Since the Latin alphabet has 26 letters, the same operation encrypts and decrypts - which is why ROT13 has been used for years on Internet forums to hide spoilers and solutions to puzzles.

Atbash

A cipher older than Caesar, known from Hebrew texts: the alphabet simply reverses (A↔Z, B↔Y, C↔X…). There is no key, so anyone who knows the rules will read the message.

GADERYPOLUKI - scout cipher

The most popular Polish substitute cipher, used in scouting. The key GA-DE-RY-PO-LU-KI consists of six pairs of letters: G↔A, D↔E, R↔Y, P↔O, L↔U, K↔I. The letters from the pairs are swapped and the rest are written unchanged. Example: SCOUT → HGYCDYZ (A→G, R→Y, E→D, and H, C and Z remain). There are also variants with other keys, e.g. PO-LI-TY-KA-RE-NU or KO-NI-EC-MA-TU-RY - the principle of operation is identical.

How to break the Caesar cipher?

The Caesar Cipher is vulnerable to two simple attacks. The first is brute force: there are only 25 possible offsets, so just try them all and choose the one that gives you the text that makes sense - in our tool it will take less than a minute. The second is frequency analysis: in each language the letters appear with a characteristic frequency (in Polish the most common are A, I, O and E). Just find the most common letter of the ciphertext and assume that it corresponds to one of them - we immediately know the probable key. The longer the text, the more reliable the result.

Popular shifts (ROT)