SPKI (stands for "Simple PKI") was an effort, now defunct, to streamline traditional PKI.
The SPKI Working Group of the IETF worked in the late 1990s but was disbanded around 2001.
"The task of the SPKI working group [was] to develop Internet standards for an IETF sponsored public key certificate format, associated signature and other formats, and key acquisition protocols. The key certificate format and associated protocols [were] to be simple to understand, implement, and use. For purposes of the working group, the resulting formats and protocols [are] known as the Simple Public Key Infrastructure, or SPKI.
"The SPKI is intended to provide mechanisms to support security in a wide range of internet applications, including IPSEC protocols, encrypted electronic mail and WWW documents, payment protocols, and any other application which will require the use of public key certificates and the ability to access them. It is intended that the Simple Public Key Infrastructure will support a range of trust models.]
In the view of this author at least, the sorts of things that need simplifying in traditional PKI are not related to certificate format or key acquisition protocols. Rather, it is the needless complexity of trying to create a legal basis for general purpose identity certificates, and "stranger-to-stranger" e-business that has made orthodox PKI so difficult. Embedded PKI, with focussed applications and usage agreements, has proven to be simple without the formal low level approaches anticipated by SPKI in the late 1990s.
Some important SPKI drafts include:
RFC 2692 - SPKI Requirements. The SPKI Working Group first established a list of things one might want to do with certificates (attached at the end of this document), and then summarized that list of desires into requirements. This document presents that summary of requirements.
RFC 2693 - SPKI Certificate Theory. This memo defines an Experimental Protocol for the Internet community. It does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested.