Is there also a protocol definition in X.509? In "Handbook of Applied Cryptography" by A. Menezes there is a reference to X.509 strong authentication protocol, nevertheless, I could not find the definition of the actual protocol, i.e. which massages are passing between the partners, in the source quoted, i.e. ITU-T X.509. Can any one help with this? Thanks

  • $\begingroup$ Doesn’t ring a bell. Could you share that quote (or page number) from HoAC? $\endgroup$ – StackzOfZtuff Apr 18 '18 at 12:16
  • $\begingroup$ Page 511 protocol 12.40 $\endgroup$ – Evgeni Vaknin Apr 18 '18 at 14:07

The strong authentication protocol referred to in the book is defined in the Annex N of "X.509 (10/16)" published by the ITU https://www.itu.int/rec/T-REC-X.509

Here is an excerpt of the standard for the two-way and strong three-way protocols:

Annex N

Considerations on strong authentication

Strong authentication makes use of PKI as specified by this Specification, which provides the basic approach to authentication. However, many authentication procedures employing this approach are possible. In general, it is the business of a specific application to determine the appropriate procedures, so as to meet the security policy of the application.

NOTE – This Specification does not specify the procedures in the detail required for implementation. However, additional standards could be envisaged that would do so, either in an application-specific or in a general-> purpose way.

  • Two-way authentication, described in clause N.3, involves, in addition, a reply from B to A. It establishes, in addition, the following:

    • that the authentication token generated in the reply actually was generated by B and was intended to be sent to A;
    • the origin, integrity and timeliness of the authentication token sent in the reply;
    • (optionally) the mutual confidentiality of part of the tokens.
  • Three-way authentication, described in clause N.4, involves, in addition, a further transfer from A to B. It establishes the same properties as the two-way authentication, but does so without the need for association timestamp checking.


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