Certificate Policy Equivalence in Cross-Certification

1. Determining Equivalence between Certificate Policies for Purposes of Cross-Certification Jimmy C. Tseng Assistant Professor of Electronic Commerce Rotterdam School of Management Erasmus University Rotterdam Tel: +31-10-408-2854 Fax: +31-10-408-9010 Email: jtseng@fbk.eur.nl

2. I. Cross-certification • The certification of one CA by another in order for a verifier to construct and verify certification paths across PKI domains • Construction of certification paths • Level of directory support • Scalability across organisations • Harmonise certificate policies TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

3. Sub-ordinated Hierarchies • Top-down from Root CA • Simple path construction • Low directory dependency • Weak scalability across organisations TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

4. Cross-certified meshes • Pair-wise between CAs • Difficult path construction • High directory dependency • Medium scalability across organisations TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

5. Hybrid model • Top-down or pair-wise • Multiple paths may exist, but simple path known • Moderate directory dependency • Medium scalability across organisations TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

6. Bridge CA • Pairwise with Bridge CA • Simple, all non-local paths traverse bridge • Medium directory dependency • Scaleable across organisations TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

7. Trust list • Recognition by verifiers • Simple but limited to paths that begin within the trust list • Low directory dependency • Fair scalability, requires intensive management TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

8. II. Certificate Policy • CP defines “applicability of a certificate to a particular community and/or class of application with common security requirements” • CP used by “certificate users to decide whether or not to trust a certificate for a particular purpose” • “Any one certificate will typically declare a single certificate policy or, possibly, be issued consistent with a small number of different policies.” – RFC2527 TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

9. Object Identifiers • “A certificate policy, which needs to be recognized by both the issuer and user of a certificate, is represented in a certificate by a unique, registered Object Identifier. The registration process follows the procedures specified in ISO/IEC and ITU standards.” – RFC2527 TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

10. Looking up a Certificate Policy • Currently no standard means of looking up an OID • How to use OIDs to represent different policy dimensions? • “The party that registers the Object Identifier also publishes a textual specification of the certificate policy, for examination by certificate users.” • Is the certificate user forced to revert back to the CPS? TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

11. Domain A Domain B (3) CA A CA B (2) Application A Application B (1) (1) Trust Entity A Entity B III. PKI Interoperation • Component-level Interoperation (standards) • Application-level Interoperation (cross platform compatibility) • Inter-domain Interoperation (harmonise certificate policies) TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

12. PKI Interdomain Interoperation • Interworking of CAs across different administrative and trust domains • Requires common or equivalent certificate policies (CP) and certification practices (CPS) • Harmonising CP and CPS are fraught with difficulties (e.g. cross-certification, policy constraints, certificate path validation) • CAs operate from different jurisdictions TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

13. IV. The Fiducia Project • Modelling the risks in interoperable public key infrastructures • Working Together • Spreading Trust • Securing Value

14. Contractual arrangements Interoperability CA A CA B Agreement CPS A CPS B Subscriber Subscriber Agreement B Agreement A Subject B Good and services Subject A RP A Payment Goverance Structure Relying Party Agreement A Modelling Contractual Risk in PKI Relationships • Modelling Business Risk in Electronic Transacting • Modelling Contractual Obligations and Liability in PKI • Non-legislative standards governing provision and use of PKI TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

15. CA Database • Database of 110 public facing CAs from 33 countries in 16 languages TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

16. CPS Database • Full-text collection of CPs and CPSs TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

17. Model Framework Legislation CPS1 CPS2 CPS3 Coding scheme Specification language Semantic Schema - entities and rules Semantic elements Substantive rules Procedural rules Support for retrieval, query, and modelling Legal Analysis • Legal and Semantic Analysis • Clarifying Roles, Obligations and Liabilities of all parties in PKI TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

18. TTP # CA# RA# IA# vets State# Digital Certificate # (subscriber certificate) (verified subject) Issued to (certificate holder) Subject# Person# Corporate# Server# contains assigned (public key) cryptographic key# pair# (private key) Semantic Analysis • Ontology of affordances (possible behaviours) • Norms (that trigger actual behaviours) TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001

19. Tools for Determining Equivalence between Certificate Policies • From certificate path validation to determining certificate policy equivalence • Textual database of certificate policy dimensions • Specification of similarities and differences across certificate policy dimensions • Basis for policy mapping and cross-certification TERENA PKI-COORD Meeting, Amsterdam, 26 Nov, 2001