Key exchange protocol

A key exchange protocol is used in cryptography to make a shared, secret key accessible to two or more communication partners. This can be done by someone transferring a key to all partners involved or by generating a new key while the protocol is being carried out. The key exchange protocol defines the exact procedure. The key is then used to encrypt and decrypt messages using symmetric encryption methods .

Key exchange protocols to solve the so-called key distribution problem , which consists in making a shared secret key accessible to the communication partners.

Originally the only way to solve the key distribution problem was to exchange a key in person or sealed by a messenger. With the advent of communication networks, protocols were developed to exchange or negotiate a session key between two parties on a public path.

Well-known protocols are

• Merkle's puzzle was discovered in 1974, but was not published until 1978, here a symmetric key is exchanged between both parties.
• Diffie-Hellman key exchange was published in 1976 by Whitfield Diffie with Martin Hellman , the first system based on asymmetric procedures
• Needham-Schroeder Protocol , published 1978, here everyone with the same trusted third party has a shared secret key

literature

• Steve Burnett Stephen Paine: RSA Security's Cryptography Official Guide. 1st edition. RSA Press, Bonn 2001, ISBN 3-8266-0780-5
• Simon Singh: Secret Messages . 4th edition. dtv, Munich 2001, ISBN 3-423-33071-6