The Random cipher is a type of substitution cipher, specifically a monoalphabetic substitution cipher. This means that you replace a letter in the plaintext with the same letter every time. For example, if you replace the letter "A" with "H", you must do that for every "A" in the entire plaintext.

The random cipher is a table that maps each letter of the plaintext to a unique letter in the ciphertext. But there's no rhyme or reason to what letters map to. Consider the following substitution table. There's no pattern to how the plaintext maps to the ciphertext. This is why it's called a Random substitution.


Consider the following random substitution table.

Original Alphabet (Plaintext)

Substitution (Ciphertext)


Based on the table "A" -> "S", "B" -> "B", "C" -> "X", "D" -> "E", "E" -> "M", etc. Let's use this to encrypt the message "ATTACK AT DAWN."

Plaintext A T T A C K   A T   D A W N
Ciphertext S A A S X Z   S A   E S Q L


To decrypt we go from the ciphertext back to the plaintext. Based on the table "S" -> "A", "B" -> "B", "X" -> "C", "E" -> "D", "M" -> "E", etc. Let's use this to decrypt the message "QSCA LKA FMA"

Ciphertext Q S C A   L K A   F M A
Plaintext W A I T   N O T   Y E T

Random Substitution Tool

Below is a random substitution generator. When you press "Randomize" it will shuffle the letters of the alphabet to create a mapping from the plaintext to the ciphertext. You can use this to encrypt/decrypt messages below the generator.

Original Alphabet (Plaintext)

Substitution (Ciphertext)

Encrypt your message

Use the tool above to set your key. When you encrypt you replace with letters in the plaintext table with the corresponding letter in the ciphertext table.

How to decrypt?

When you decrypt you replace the letters from the ciphertext table with the corresponding letter from the plaintext table.

Decrypt your message:

Use the shift tool from above.