Cryptosystem
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Because of this ambiguity, the outdated RFC 2828 advised against the use of this term.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.
Formal definition
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 .
that .
See also
Individual evidence
 ↑ Johannes Buchmann : Introduction to Cryptography . 4th enlarged edition. Springer, Berlin a. a. 2008, ISBN 9783540744511 , pp. 59 .
 ↑ Bruce Schneier : Applied Cryptography . Protocols, Algorithms and Source Code in C . AddisonWesley, Bonn a. a. 1996, ISBN 3893198547 , pp. 4 .
 ↑ Friedrich L. Bauer : Deciphered secrets. Methods and maxims of cryptology . 3rd, revised and expanded edition. Springer, Berlin a. a. 2000, ISBN 3540679316 , 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 9783834802538 , pp. 2 .

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R. Shirey: RFC 2828  Internet Security Glossary (200005)
 cryptosystem
 (D) ISDs SHOULD NOT use this term as an abbreviation for cryptographic system. (For rationale, see: crypto.)
 crypto
 Except as part of certain longestablished terms listed in this Glossary, ISDs SHOULD NOT use this abbreviated term because it may be misunderstood. Instead, use "cryptography" or "cryptographic".

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R. Shirey: RFC 4949  Internet Security Glossary, Version 2 (200708)
 cryptosystem
 (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 keyagreement 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 0387207562 .