SPNEGO

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SPNEGO stands for Simple and Protected GSSAPI Negotiation Mechanism. SPNEGO is a standard GSSAPI pseudo-mechanism for peers to determine which GSSAPI mechanisms are shared, select one and then establish a security context with it. SPNEGO is sometimes pronounced or spelt "spengo".

SPNEGO's most visible use is in Microsoft's "HTTP Negotiate" authentication extension. It was first implemented in Internet Explorer 5.01 and IIS 5.0 and provided single sign-on capability later marketed as Windows Integrated Authentication. The negotiable sub-mechanisms included NTLM and Kerberos, both used in Active Directory.

The HTTP Negotiate extension was later implemented with similar support in Mozilla 1.7beta, Mozilla Firefox 0.9, and Konqueror 3.3.1.

[edit] History of the SPNEGO standard

19 February 1996 - Eric Baize and Denis Pinkas publish the internet draft Simple GSS-API Negotiation Mechanism (draft-ietf-cat-snego-01.txt).
17 October 1996 - The mechanism is assigned the object identifier 1.3.6.1.5.5.2 and is abbreviated snego.
25 March 1997 - Optimistic piggybacking of one mechanism's initial token is added. This saves a round trip.
22 April 1997 - The "preferred" mechanism concept is introduced. The draft standard's name is changed from just "Simple" to "Simple and Protected" (spnego).
16 May 1997 - Context flags are added (delegation, mutual auth, etc.). Defences are provided against attacks on the new "preferred" mechanism.
22 July 1997 - More context flags are added (integrity and confidentiality).
18 November 1998 - The rules of selecting the common mechanism are relaxed. Mechanism preference is integrated into the mechanism list.
4 March 1998 - An optimisation is made for an odd number of exchanges. The mechanism list itself is made optional.

Final December 1998 - DER encoding is chosen to disambiguate how the MIC is calculated. The draft is submitted for standardisation as RFC 2478.
October 2005 - Interoperability with Microsoft implementations is addressed. Some constraints are improved and clarified and defects corrected. Published as RFC 4178, although it is now non-interoperable with strict implementations of now-obsoleted RFC 2478.