In Cryptography, encryption is the process of encoding messages (or information) in such a way that eavesdroppers or hackers cannot read it, but only authorized parties can. The Encryption Model defines the encryption of plaintext into ciphertext and decryption of ciphertext into plaintext.

Plaintext is the message that is to be encrypted. It is transformed by a function that is parameterized by a key.  CipherText is the output of the encryption process that is transmitted often by a messenger or radio.  

Encryption Model

In an encryption scheme, the intended information or message, referred to as plaintext, is encrypted using an encryption algorithm – a cipher – generating ciphertext that can be read only if decrypted. For technical reasons, an encryption scheme usually uses a pseudo-random encryption key generated by an algorithm.

The intruder may hear and accurately copies down the complete ciphertext. However, unlike the intended recipient, he does not know what the decryption key is and so cannot decrypt the ciphertext easily. Sometimes the intruder can not only listen to the communication channel (passive intruder) but can also record messages and play them back later, inject his own messages, or modify legitimate messages before they get to the receiver (active intruder). The art of breaking ciphers is known as Cryptanalysis, and the art of devising them (Cryptography) are collectively known as Cryptology.