Caesar Cipher
Encode and decode text using the Caesar cipher (ROT shift cipher). Supports custom shift values and brute-force all 25 possible decryptions at once.
113 (ROT13)25
Shift visualization (shift = 13)
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
A
B
C
D
E
F
G
H
I
J
K
L
M
Plain → Cipher
How to Use Caesar Cipher
- 1Enter the text you want to encode or decode.
- 2Choose a shift value (1–25) or use the ROT13 shortcut.
- 3Toggle between encode and decode mode.
- 4Use "Show all shifts" to brute-force decrypt unknown ciphertext.
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Frequently Asked Questions
What is the Caesar cipher?▾
The Caesar cipher is one of the oldest and simplest encryption techniques, named after Julius Caesar who used it to protect military messages. It is a substitution cipher where each letter in the plaintext is shifted a fixed number of positions down the alphabet. With a shift of 3, A becomes D, B becomes E, Z becomes C (wrapping around). Non-alphabetic characters (numbers, punctuation, spaces) are typically left unchanged.
What is ROT13?▾
ROT13 is a Caesar cipher with a shift of 13 — exactly half the 26-letter alphabet. It is self-inverse: applying ROT13 twice returns the original text. ROT13 is commonly used in online forums to hide spoilers or puzzle answers, since it is trivially reversible. It provides no cryptographic security and is purely an obfuscation technique.
How do you decrypt a Caesar cipher without knowing the shift?▾
Since there are only 25 possible shifts (1-25), brute force is trivial. Try all 25 shifts and identify which one produces readable English text. Alternatively, use frequency analysis: in English, E is the most common letter (~13%), followed by T, A, O, I, N. Find the most frequent letter in the ciphertext — it likely corresponds to E. The shift difference between that letter and E is the cipher key.
Is the Caesar cipher secure?▾
No. The Caesar cipher offers essentially zero security by modern standards. With only 25 possible keys, it can be broken in seconds by exhaustive search (brute force). Even without a computer, frequency analysis can break it in minutes. It is a valuable educational tool for understanding classical cryptography, but should never be used for actual security purposes. Modern encryption uses algorithms like AES, RSA, and ChaCha20.
What are other classical ciphers?▾
Classical ciphers include: Vigenère cipher (uses a keyword for polyalphabetic substitution, harder to break), Atbash (reverses the alphabet: A↔Z, B↔Y), ROT47 (shifts all printable ASCII characters by 47), Playfair cipher (digraph substitution using a 5×5 key square), Rail fence cipher (transposition cipher using zigzag pattern), and One-time pad (theoretically unbreakable but impractical). All are now obsolete for security applications.