In cryptography, decryption is the conversion of ciphertext into plaintext.

Decryption is an operation which transforms a ciphertext message into plaintext using a cryptographic algorithm called a cipher. Like encryption, decryption in modern ciphers is performed by using a specific algorithm and a secret, called the key.

The decryption primitive.

Decryption is the reverse process of encryption and if the key stays secret, is mathematically hard to perform. How hard it is depends on how secure the cryptographic algorithm is, and that in itself is subject to change as the study of cryptanalysis advances.

See also