Cryptosystem

A cryptosystem refers to a suite of algorithms needed to implement a particular form of encryption and decryption.

Typically, a cryptosystem consists of three algorithms: one for key generation, one for encryption, and one for decryption. The term cipher (or sometimes cypher) is often used to refer to a pair of algorithms, one for encryption and one for decryption. Therefore, the term "cryptosystem" is most often used when the key generation algorithm is important. For this reason, the term "cryptosystem" is almost always used to refer to public key techniques, while "cipher" and "cryptosystem" are both used for symmetric key techniques.

The term cryptosystem is also used as shorthand for "cryptographic system," which means something quite different. A cryptographic system is any computer system that involves cryptography; here, secrecy is not necessarily the aim, and many more algorithms and protocols may be needed. For instance, a system for secure electronic mail may include methods for digital signatures, cryptographic hash functions, key management techniques, and so on. It is cryptographic systems that users interact with directly.