Ciphertext

In cryptography, ciphertext or cyphertext is the result of encryption performed on plaintext using an algorithm, called a cipher. Ciphertext is also known as encrypted or encoded information because it contains a form of the original plaintext that is unreadable by a human or computer without the proper cipher to decrypt it. Decryption, the inverse of encryption, is the process of turning ciphertext into readable plaintext. Ciphertext is not to be confused with codetext because the latter is a result of a code, not a cipher.

Symmetric key example

Let be the plaintext message that Alice wants to secretly transmit to Bob and let be the encryption cipher, where is a secret key. Alice must first transform the plaintext into ciphertext, , in order to securely send the message to Bob.

Both Alice and Bob must know the choice of key, , or else the ciphertext is useless. Once the message is encrypted as ciphertext, Alice can safely transmit it to Bob (assuming no one else knows the key). In order to read Alice's message, Bob must decrypt the ciphertext using which is known as the decryption cipher, .