Determining Equivalence between Certificate Policies for Purposes of Cross-Certification
Jimmy C. TsengAssistant Professor of Electronic Commerce
Rotterdam School of Management Erasmus University Rotterdam
Tel: +31-10-408-2854 Fax: +31-10-408-9010 Email: [email protected]
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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 pathsLevel of directory supportScalability across organisationsHarmonise certificate policies
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Sub-ordinated HierarchiesTop-down from Root CASimple path constructionLow directory dependencyWeak scalability across organisations
Root CA
Subordinate CA(level 2)
Subordinate CA(level 1)
Subordinate CA(level 1)
Subordinate CA(level 2)
Subordinate CA(level 2)
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Cross-certified meshesPair-wise between CAsDifficult path constructionHigh directory dependencyMedium scalability across organisations
Local CA ELocal CA BLocal CA A Local CA DLocal CA C
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Hybrid modelTop-down or pair-wiseMultiple paths may exist, but simple
path knownModerate directory dependencyMedium scalability across organisations
Subordinate CA(level 2)
Local CA B(level 1)
Local CA A(level 1)
Subordinate CA(level 2)
Subordinate CA(level 2)
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Bridge CAPairwise with Bridge CASimple, all non-local paths traverse bridgeMedium directory dependencyScaleable across organisations
Bridge CA(cross-
certificationauthority)
Subordinate CA(level 2)
CA B(level 1)
CA A(level 1)
Subordinate CA(level 2)
Subordinate CA(level 2)
CA C(level 1)
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Trust list
Recognition by verifiers
Simple but limited to paths that begin within the trust list
Low directory dependency
Fair scalability, requires intensive management
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II. Certificate PolicyCP defines “applicability of a certificate to a pa
rticular 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
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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
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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?
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III. PKI Interoperation Component-level Interoperation
(standards) Application-level Interoperation
(cross platform compatibility) Inter-domain Interoperation
(harmonise certificate policies)
CA A
Domain A
Entity A
Application A
CA B
Domain B
Entity B
Application B
Trust (1)(1)
(2)
(3)
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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
IV. The Fiducia ProjectModelling the risks in
interoperable public key infrastructures
Working TogetherSpreading TrustSecuring Value
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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
Subject A Subject B
RP AGood and services
Payment
CA BCPS B
CA ACPS A
GoveranceStructure
Contractual arrangements
SubscriberAgreement A
Relying PartyAgreement A
SubscriberAgreement B
InteroperabilityAgreement
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CA DatabaseDatabase of 110 public facing CAs
from 33 countries in 16 languages
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CPS DatabaseFull-text collection of CPs and CPSs
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Legal AnalysisLegal and Semantic AnalysisClarifying Roles, Obligations and
Liabilities of all parties in PKI
Model Framework
Legislation
CPS1 CPS2
Semantic Schema - entities and rules
Semantic elements
Substantive rules
Procedural rules
Coding scheme
Specification language
Support for retrieval, query, and modelling
CPS3
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Semantic AnalysisOntology of affordances (possible behaviour
s)Norms (that trigger actual behaviours)
State#
Subject#
TTP #
Digital Certificate #
Person#Corporate#Server#
CA#RA#IA#
(certificate holder)
Issued to
(public key)assigned
pair#
vets
cryptographic key#(private key)
(verifi
ed subject)
(subscriber certificate)
contains
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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