SPKI analysis in strand space

1. SPKI analysis in strand space Alex Vidergar, 1Lt, USAFAir Force Institute of Technology Graduate School of Computer Science & Engineering Thesis Advisor: Robert Graham, Maj, USAF

2. Overview • SPKI • what it is and why we use it • Strand Space • How this tool was used effectively • Example Analysis • Transport Layer Security (TLS) • Conclusions about new security properties • Authorizations

3. Simple Public Key Infrastructure • Championed by Ron Rivest (RSA) and Carl Ellison (Intel) • Simple Distributed Security Infrastructure (SDSI) and SPKI merged in the 90s • Developed to overcome shortcoming in the currently deployed PKI (X.509) • Two types of certificates Name & Authorization

4. X.509 Shortcomings • Unrealistic Goals • Global reach of the x.500 directory • Single global standard • Unique names in one namespace • Privacy • Participation in the network may unwillingly revealing details about organization • Lack of Flexibility • Updated information impossible • Multiple keys unsupported

5. SPKI Solutions • Egalitarian Design • Every Principal acts as Certificate Authority (CA) • Local Names • Humans tend to relate well to things they name themselves • Local name space • Allows unique names to be applied as understood by the principals that will be using them • Fully qualified names act globally • Alice’s Bob’s Charlie ≠ Allison’s Bob’s Charlie

6. SPKI Solutions • Delegation of Authority • Delegation bit • University Example • University Enrollment • Course Enrollment • Department • School - student

7. SPKI: Authorization Tags • Customized to applications • Once again not standardized • Flexibility • Security through obscurity? • What is access of 10 mean? • More importantly, meaningful to the issuers of access to a resource

8. SPKI: Flexibility or Meager Design? • Constant theme of Flexibility • Very Vague Specification • Highly customizable • Requires diligence in implementation • Easily integrated into a system • Potential security issues may arise Solution: Strand space analysis

9. Strand Space • Existing Strand Space Model • Public Key Protocol • Diffie-Hellman • Injective hash function • Signatures in addition to encryptions • Mixed Strand Space • Disparate protocols operating in the same space • Respect • Disjoint Encryption

10. Strand Space : Merge • Mixed PKI Strand Space • Amalgamation of needed features of previous strand space models • Ideal environment for testing SPKI protocols being integrated into other systems

11. TLS : Analysis • Ideal analysis protocol: Transport Layer Security • Arguably the most widely used Internet protocol for secure transactions • Intrinsic use of certificates • Uses x.509 • Layered protocol execution • TLS > DH > Resume

12. TLS : modifications • TLS uses x.509 certificates • Mayweh implements SSL with SPKI • Substitute x.509 for SPKI name certs • Functionally identical • Limited Network security • Assumed operating in secure environment

13. TLS : the sweet Onion • TLS is a layer of protocols • TLS itself is a shell • Arranges for other protocols to run • Does not provide security • Security provided by sub protocols • Diffie-Hellman • RSA

14. TLS : Primary Protocols Server Authentication Protocol • Client unauthenticated

15. TLS : Primary Protocols Server & Client Authentication Protocol • Both principals authenticated

16. Mixed Strand Space : Resume Resume Protocol • Inherently uninteresting • Provides only a recount of a previously executed session • Relies on message digest for coordination and agreement

17. Mixed Strand Space : Certificate Chain Discovery • Certificate Chain Discovery Protocol • Designed from the ground up with TLS in mind • establish authentication of CA • validation of certificate • maintain security of primary protocol

18. Mixed Strand Space : Certificate Chain Discovery • Possible to assume disjoint set of keys • therefore disjoint encryption is trivial • Message formats designed disjointly • once again simple proof of respect if designed properly

19. Analysis • Respect • Concept born in paper Mixed Strand Spaces • Supplemented • Method for defining respect • Characterize test components • Identify sets of messages • Applied to Diffie-Hellman • Protocol design based on Respect • SPKI Certificate Chain Discovery • Disjoint Encryption • Respect of primary protocol’s test components • Necessary to Prove for each protocol as primary?

20. Analysis Disjoint Encryption • Protocol Independence through Disjoint Encryption • Better Refined concept of respect → Independence • Disjoint set of test components • Previous notion of Respect • covers naïve case of disjoint sets • Allows more complex secondary protocols to be designed • In the CCD Protocol Design Case • CCD design from respect is indeed Disjoint Encryption • Disjoint Outbound simple case: no shared terms • Disjoint Inbound • Visual representation of mixed strand spaces • Problematic with entwined sub-protocols

21. Simple and Powerful • Signed statements are certifications • An authority is an authority • Certificate Authorities traditionally are simply name authorities • Does not have to be limited to names • Authorizations are thus provided by an authorization principal • Already incorporated with authorization certificates in SPKI standard • Explicit Rely-Guarantee Functionality

22. Summary • SPKI • Vague specification makes it flexible • Requires diligence in implementation • Strand Space • Mixed-PKI strand space • TLS • Ideal testing ground for SPKI analysis • Authorization • Intrinsic to SPKI standard • CA are trusted to provide

23. Questions