Cryptography is the art or science of secret writing or more exactly of storing information for a shorter or longer period of time in a form which allows it to be revealed to those you wish to see it yet hides it from all others A cryptosystem is a method to accomplish this Cryptanalysis is the practice of defeating such attempts to hide information Cryptology includes both cryptography and cryptanalysis The original information to be hidden is called plaintext The hidden information is called ciphertext Encryption is any procedure to convert plaintext into ciphertext Decryption is any procedure to convert ciphertext into plaintext Plaintext is converted into ciphertext by means of an encryption engine again generally a computer program whose operation is fixed and determinate the encryption method but which functions in practice in a way dependent on a piece of information the encryption key which has a major effect on the output of the encryption process A cryptosystem could be designed which made use of several different methods of encryption the particular method chosen for a particular encryption process being keydependent The combination of encryption methods results again in an encryption method which is just as deterministic as a simpler cryptosystem although probably harder for a cryptanalyst to crack A good cryptosystem should in fact vary the details of its encryption method in a keydependent way though high security does not require the combination of distinct encryption algorithms The result of using the decryption method and the decryption key to decrypt ciphertext produced by using the encryption method and the encryption key should always be the same as the original plaintext except perhaps for some insignificant differences