From Wikipedia, the free encyclopedia

Simple and Protected GSSAPI Negotiation Mechanism (SPNEGO), often pronounced "spenay-go", is a GSSAPI "pseudo mechanism" used by client-server software to negotiate the choice of security technology. SPNEGO is used when a client application wants to authenticate to a remote server, but neither end is sure what authentication protocols the other supports. The pseudo-mechanism uses a protocol to determine what common GSSAPI mechanisms are available, selects one and then dispatches all further security operations to it. This can help organizations deploy new security mechanisms in a phased manner.

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 Integrated Windows 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:


  • 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 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.). Defenses 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.
  • December 1998 (Final) – 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.


  1. ^ Mozilla bug 17578: I want Kerberos authentication and TGT forwarding
  2. ^ "Konqueror has SPNEGO support". Apache and Kerberos tutorial. Archived from the original on 19 April 2005. Retrieved 30 May 2005.
  3. ^ "Support for SPNEGO authentication". Google Chrome Enhancement Request. Archived from the original on 11 November 2012. Retrieved 20 November 2010.


External links[edit]

  • RFC 4178 The Simple and Protected GSS-API Negotiation Mechanism (obsoletes RFC 2478).
  • RFC 4559 SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows