Symmetric-key algorithm

A symmetric cryptosystem is a cryptosystem in which, in contrast to an asymmetric encryption system, both parties use the same key. In some symmetrical procedures (eg IDEA ) are the two keys are not identical, but can be calculated easily apart. This article is limited to the representation of encryption methods. Sometimes called message authentication codes are called symmetric cryptosystem.

Formally, a symmetric encryption method, a tuple, where the set of possible plaintexts, the set of possible ciphers and the amount of possible keys. is the encryption function and decryption function. The process must be correct in the sense that applies to everyone.

It splits the symmetric methods in block ciphers and stream ciphers based methods. With stream ciphers, the plaintext is encrypted character by character, in order to obtain the ciphertext, or decrypted to obtain the plaintext. A block cipher operates with a fixed block size and encrypt or decrypt multiple characters in one step. To encrypt your texts of any length, operating modes are defined, which determine how the block cipher is being used.

The big disadvantage of symmetric methods is the use of one and the same key for encryption and decryption, ie in addition to the encrypted information and the key needs to be transmitted. The problem with the use of symmetric method is that the key has to be transmitted over a secure channel, for the security of the method depends on the secrecy of the key. Previously, the key is typically delivered by a messenger personally. Since the 1970s, with the Diffie -Hellman key exchange asymmetric key exchange protocols are known with which keys can be transmitted securely via a wiretapped channel. Another possibility is the use of asymmetric encryption method to the symmetric key to encrypt itself and to transfer him so protected over an insecure channel. When communicating so they can be exploited with these hybrid encryption the benefits ( for example, the higher speed) symmetric encryption, while the key is protected by the asymmetric encryption before accessing an attacker.

Symmetric method has been around since ancient times. Until the 1970s, only symmetric methods were ever known.

Method

  • AES ( Advanced Encryption Standard) or Rijndael: the U.S. encryption standard, the successor of the DES; developed by Joan Daemen and Vincent Rijmen block encryption method
  • DES (Data Encryption Standard ) or Lucifer: by October 2000, the encryption standard of the United States. Lucifer, the method was developed in 1974 by IBM. The version for the home called the Data Encryption Algorithm ( DEA).
  • Triple DES: a further development of the DES method; three times slower, but safer by orders of magnitude
  • IDEA (International Data Encryption Algorithm ): a 1990 developed at the ETH Zurich block encryption method; Software patented by Ascom Systec; Application in PGP
  • Blowfish: developed by Bruce Schneier in 1993 block encryption method unpatented,
  • QUISCI ( Quick Stream Cipher ): very fast stream cipher method by Stefan Müller developed unpatented 2001
  • Twofish: Block encryption method from Counterpane Team; will, inter alia, used in Microsoft Windows.
  • CAST -128, CAST -256: Block encryption method of Carlisle M. Adams, unpatented
  • RC2, RC4, RC5, RC6 ( " Rivest Cipher " ): several encryption methods of Ronald L. Rivest
Public-key cryptography Ancient history Lucifer (cipher) Blowfish (cipher) Ron Rivest Integrated Authority File
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