Cryptosystem

There are two different meanings of the word cryptosystem. 
 One is used by the cryptographic community.
 The other is a general meaning which is how the word cryptosystem is understood by the public.

 General meaning 

In this meaning, the term cryptosystem is used as shorthand,  or as an abbreviation for "cryptographic system". A cryptographic system is any computer system that involves cryptography. Such systems include for instance, a system for secure electronic mail which might include methods for digital signatures, cryptographic hash functions, key management techniques, and so on.

 Meaning in the cryptographic community 

In this meaning, a cryptosystem refers to a set of algorithms needed to implement a method of encryption and decryption. 

Typically, a cryptosystem consists of three algorithms: 
 Key generation algorithm.
 Encryption algorithm.
 Decryption algorithm.  

The term cipher (sometimes cypher) is often used to refer to a pair of (encryption/decryption) algorithms. Therefore, the term "cryptosystem" is most often used when the key generation algorithm is important.  For this reason, the term "cryptosystem" is commonly used to refer to public key techniques; however both "cipher" and "cryptosystem" are used for symmetric key techniques.

 "Cryptographic system" vs. "cryptosystem" 

The Internet Security Glossary RFC 2828 advises against using the term "cryptosystem", giving the following definitions.
cryptosystem
(D) ISDs SHOULD NOT use this term as an abbreviation for cryptographic system. (For justification, see: crypto.)
crypto
ISDs SHOULD NOT use this abbreviated term because it may be misunderstood. Instead, use "cryptography" or "cryptographic".

References

Category:Cryptography