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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:

A,B - network nodes.
KU_x - public key of node x.
KR_x - private key of x.
N_x - nonce chosen by x.
ID_x - unique identifier of x.
E_k - public-key encryption using key k.
S_k - digital signature using key k.
K - random session key chosen by the KDC.
|| - concatenation.

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

Message exchange[edit]

1) A \rightarrow KDC : ID_A || ID_B
2) KDC \rightarrow A : S_{KR_{KDC}}[ID_B||KU_B]
3) A \rightarrow B : E_{KU_B}[N_A||ID_A]
4) B \rightarrow KDC: ID_B||ID_A||E_{KU_{KDC}}[N_A]
5) KDC \rightarrow B : S_{KR_{KDC}}[ID_A||KU_A]||E_{KU_B}[S_{KR_{KDC}}[N_A||K||ID_B||ID_A]]
6) B \rightarrow A : E_{KU_A}[S_{KR_{KDC}}[N_A || K ||  ] || N_B]]
7) A \rightarrow B : E_{K}[N_B]

The original version of the protocol[4] had the identifier ID_A omitted from lines 5 and 6, which did not account for the fact that N_A 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. pp. 39–52. doi:10.1109/2.108052.