Create and solve substitution ciphers

On this page you can create and solve simple substitution ciphers. In a substitution cipher, each letter of the alphabet is replaced with a different letter.

A Caesar cipher is the simplest type of substitution cipher. Each letter of the alphabet is shifted by a fixed number of places. For example, with a shift of 1, every occurrence of the letter A becomes a B, every B becomes a C, and so on. The sequence "wraps around", so Z gets shifted to A. The reason this cipher is so simple is that in English there are only 25 possible ways to shift the alphabet, so it takes a maximum of 25 decoding attempts to find the original text. 

For example, using a Caesar cipher with a shift of 1, HELLO becomes IFMMP. With a shift of 2, it's JGNNQ.

An alphabet reversal cipher is another special case of a substitution cipher, where A becomes Z, B becomes Y, C becomes X, and so on. The encoding/decoding key looks like this:

ABCDEFGHIJKLMNOPQRSTUVWXYZ
ZYXWVUTSRQPONMLKJIHGFEDCBA

Other substitution ciphers are more complicated and harder to decode. Every letter A-Z is replaced uniquely by some other letter A-Z, but it is done randomly, not by a simple shifting of the alphabet. You have to decode one letter at a time. 

The programs on this page are JavaScript translations of my original encoding and decoding programs for Microsoft Visual C++ and Borland C++.

The text you enter here is processed by JavaScript in your browser. It's not sent back to this website, so I don't see it.

However, substitution ciphers, and Caesar ciphers in particular, don't provide any real security. They are very easy to break and are best viewed only as fun puzzles.

Create a cipher

Enter your plain text here:

Read your ciphered text here:

Decode a cipher

Enter your enciphered text here:

To test for a Caesar cipher, Start Without Help, then click Rotate 26 times.
If that fails, Start With ETAOIN, which tries to assign the highest frequency letters to ETAOIN.

Letter frequencies in the ciphered text:

Decoded text, color coded to show locked letters, but in one long paragraph:

Decoded plain text, formatted same as the input:

Command Line. Enter the letters to change and click an action button below:

• You can enter uppercase or lowercase letters. All are converted to upper case.
• To change all T to E, enter TE in the box, then click Swap.
• To lock the phrase THIS IS, enter THIS IS in the box, then click Lock. Duplicated letters don't matter.
• Unlock works the same way.
• Rotate is mostly for doing an initial Caesar Cipher test after Start Without Help, but it can also help you get new ideas later in the decoding process. Locked letters also rotate.
• For security reasons, some characters in the input text are converted to dots (.) in the output.

Ciphers to solve. Random difficulty. Copy and paste above. One of them is a Caesar cipher.