Yahalom (protocol)

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Yahalom is an authentication and secure key-sharing protocol designed for use on an insecure network such as the Internet. Yahalom uses a trusted arbitrator to distribute a shared key between two people. This protocol can be considered as an improved version of Wide Mouth Frog protocol (with additional protection against man-in-the-middle attack), but less secure than the Needham–Schroeder protocol.

Protocol description[edit]

If Alice (A) initiates the communication to Bob (B) with S is a server trusted by both parties, the protocol can be specified as follows using security protocol notation:

  • A and B are identities of Alice and Bob respectively
  • is a symmetric key known only to A and S
  • is a symmetric key known only to B and S
  • and are nonces generated by A and B respectively
  • is a symmetric, generated key, which will be the session key of the session between A and B

Alice sends a message to Bob requesting communication.

Bob sends a message to the Server encrypted under .

The Server sends to Alice a message containing the generated session key and a message to be forwarded to Bob.

Alice forwards the message to Bob and verifies has not changed. Bob will verify has not changed when he receives the message.

See also[edit]