A cryptosystem is generally a system that has to do with cryptography . The term is used as a fixed term in the name RSA cryptosystem . However, the term cryptosystem means different things in different contexts. Some authors limit the term cryptosystem to encryption methods . Others also use it for other cryptographic systems such as digital signatures .
Because of this ambiguity, the outdated RFC 2828 advised against the use of this term. In the current RFC 4949 , which replaced RFC 2828 , the term "cryptosystem" is defined as a contraction of "cryptographic system". The definition of a cryptographic system includes both possible meanings, but the more general one is preferred. Both RFCs are not an Internet standard, but are classified as informational.
Mathematically, a cryptosystem is defined as the tuple , which has the following properties.
- is the plain text. The elements of are the plaintext.
- is the encrypted text (or ciphertext). The elements of are the ciphertext.
- is defined as the key. The elements of are key
- with the function . Is the encryption function for .
- with the function . Is the decryption function for .
- Johannes Buchmann : Introduction to Cryptography . 4th enlarged edition. Springer, Berlin a. a. 2008, ISBN 978-3-540-74451-1 , pp. 59 .
- Bruce Schneier : Applied Cryptography . Protocols, Algorithms and Source Code in C . Addison-Wesley, Bonn a. a. 1996, ISBN 3-89319-854-7 , pp. 4 .
- Friedrich L. Bauer : Deciphered secrets. Methods and maxims of cryptology . 3rd, revised and expanded edition. Springer, Berlin a. a. 2000, ISBN 3-540-67931-6 , pp. 7 .
- Albrecht Beutelspacher : Kryptologie: An introduction to the science of encryption, concealment and concealment. Without any secrecy, but not without deceitful rogue, presented for the benefit and delight of the general public . 9th, updated edition. Vieweg + Teubner, Wiesbaden 2009, ISBN 978-3-8348-0253-8 , pp. 2 .
R. Shirey: RFC 2828 - Internet Security Glossary (2000-05)
- (D) ISDs SHOULD NOT use this term as an abbreviation for cryptographic system. (For rationale, see: crypto.)
- Except as part of certain long-established terms listed in this Glossary, ISDs SHOULD NOT use this abbreviated term because it may be misunderstood. Instead, use "cryptography" or "cryptographic".
R. Shirey: RFC 4949 - Internet Security Glossary, Version 2 (2007-08)
- (I) Contraction of the "cryptographic system".
- cryptographic system
- 1. (I) A set of cryptographic algorithms together with the key management processes that support use of the algorithms in some application context.
- Usage: IDOCs SHOULD use definition 1 because it covers a wider range of algorithms than definition 2.
- 2. (O) "A collection of transformations from plain text into cipher text and vice versa [which would exclude digital signature, cryptographic hash, and key-agreement algorithms], the particular transformation (s) to be used being selected by keys. The transformations are normally defined by a mathematical algorithm. " [X509]
- Johannes A. Buchmann: Introduction to Cryptography , 2nd. Edition, Springer ,, ISBN 0-387-20756-2 .