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In cryptography, Woo–Lam refers to various computer network authentication protocols designed by Simon S. Lam and Thomas Woo.[1][2] The protocols enable two communicating parties to authenticate each other's identity and to exchange session keys, and involve the use of a trusted key distribution center (KDC) to negotiate between the parties. Both symmetric-key and public-key variants have been described. However, the protocols suffer from various security flaws, and in part have been described as being inefficient compared to alternative authentication protocols.[3]

Public-key protocol[edit]


The following notation is used to describe the algorithm:

- network nodes.
- public key of node .
- private key of .
- nonce chosen by .
- unique identifier of .
- public-key encryption using key .
- digital signature using key .
- random session key chosen by the KDC.
- concatenation.

It is assumed that all parties know the KDC's public key.

Message exchange[edit]

The original version of the protocol[4] had the identifier omitted from lines 5 and 6, which did not account for the fact that is unique only among nonces generated by A and not by other parties. The protocol was revised after the authors themselves spotted a flaw in the algorithm.[1][3]

See also[edit]


  1. ^ a b T.Y.C. Woo, S.S. Lam (March 1992). "Authentication Revisited". Computer. IEEE. 25 (3). doi:10.1109/2.121502.
  2. ^ Colin Boyd, Anish Mathuria (2003). Protocols for authentication and key establishment. Springer. p. 78 and 99. ISBN 978-3-540-43107-7.
  3. ^ a b Stallings, William (2005). Cryptography and Network Security Principles and Practices, Fourth Edition. Prentice Hall. p. 387. ISBN 0-13-187316-4.
  4. ^ Thomas Y.C. Woo, Simon S. Lam (January 1992). "Authentication for Distributed Systems". 25 (1). IEEE: 39–52. doi:10.1109/2.108052.