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2013-10-15T14:38:03Z

167.236.248.70: /* Velocity */ typo 'geven' - 'given'

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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 [[Needham-Schroeder]].

== Protocol description ==
If [[Alice and Bob|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
* <math>K_{AS}</math> is a [[symmetric key]] known only to A and S
* <math>K_{BS}</math> is a symmetric key known only to B and S
* <math>N_A</math> and <math>N_B</math> are [[cryptographic nonce|nonces]] generated by A and B respectively
* <math>K_{AB}</math> is a symmetric, generated key, which will be the [[session key]] of the session between A and B

<math>A \rightarrow B: A, N_A</math>
:Alice sends a message to Bob requesting communication.
<math>B \rightarrow S: B,\{A, N_A, N_B\}_{K_{BS}}</math>
:Bob sends a message to the Server encrypted under <math>K_{BS}</math>.
<math>S \rightarrow A: \{B, K_{AB}, N_A, N_B\}_{K_{AS}}, \{A, K_{AB}\}_{K_{BS}}</math>
:The Server sends to Alice a message containing the generated session key <math>K_{AB}</math> and a message to be forwarded to Bob.
<math>A \rightarrow B: \{A, K_{AB}\}_{K_{BS}}, \{N_B\}_{K_{AB}}</math>
:Alice forwards the message to Bob and verifies <math>N_A</math> has not changed. Bob will verify <math>N_B</math> has not changed when he receives the message.


== See also ==
* [[Kerberos (protocol)|Kerberos]]
* [[Otway-Rees]]
* [[Neuman-Stubblebine protocol|Neuman-Stubblebine]]

==References==
* {{cite book
|last = Schneier
|first = Bruce
|authorlink = Bruce Schneier
|title = Applied Cryptography
|publisher = [[John Wiley & Sons]]
|year = 1996
|pages = 57–58
|isbn = 0-471-12845-7}}
* M. Burrows, M. Abadi, R. Needham [http://www.hpl.hp.com/techreports/Compaq-DEC/SRC-RR-39.pdf A Logic of Authentication], Research Report 39, Digital Equipment Corp. Systems Research Center, Feb. 1989
* M. Burrows, M. Abadi, R. Needham [http://portal.acm.org/citation.cfm?id=77649 A Logic of Authentication]. ACM Transactions on Computer Systems, v. 8, n. 1, Feb. 1990, pp. 18—36

<references/>

[[Category:Cryptographic protocols]]
[[Category:Computer access control protocols]]

{{crypto-stub}}

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