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Public-Key Infrastructure (PKI)

Public-Key Infrastructure (PKI). What is PKI?. Pervasive security infrastructure whose services are implemented and delivered using public-key concepts and techniques -(C. Adams, S. Lloyd) Secure sign-on End-user transparency Comprehensive security. Business Drivers. Cost savings

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Public-Key Infrastructure (PKI)

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  1. Public-Key Infrastructure (PKI) CSE 5349/7349

  2. What is PKI? • Pervasive security infrastructure whose services are implemented and delivered using public-key concepts and techniques -(C. Adams, S. Lloyd) • Secure sign-on • End-user transparency • Comprehensive security CSE 5349/7349

  3. Business Drivers • Cost savings • Inter-operability • Uniformity • Potential for validation/testing • Choice of provider Consider the analogy with BUS architecture vs. point-to-point links CSE 5349/7349

  4. Components and Services • Certification authority • Certificate repository • Certificate revocation • Key backup and recovery • Automatic key update • Key history • Cross-certification • Support for non-repudiation • Time stamping CSE 5349/7349

  5. Certificates • Certificate vs. signature • Types of certificates • X.509 (v1, v2, v3) • Simple Public Key Infrastructure (SPKI) certificates • PGP certificates • Attribute certificates CSE 5349/7349

  6. Certificate Format • Version number • Serial number • Signature algorithm identifier • Issuer name • Period of validity • Subject name • Subject’s public-key info. • Issuer unique ID • Subject unique ID • Extensions • Signature CSE 5349/7349

  7. Key/Certificate Life Cycle • Initialization • Registration • Key-pair generation (where?) • Certificate creation and dissemination • Key backup • Issued • Certificate retrieval • Certificate validation • Cancellation • Expiration • Revocation • History and archive CSE 5349/7349

  8. Certificate Path Processing • Eventual objective is to determine whether the key in a given certificate can be trusted • Path construction – aggregation of certificates to form a complete path • Path validation – validating each certificate in the path Target certificate is trusted only if every certificate in the path are trustworthy CSE 5349/7349

  9. X.509 Hierarchy • Forward certificates • Certificate of X generated by other CAs • Reverse certificates • Certificates of other CAs generated by X • Example from the book (showed in last class) CSE 5349/7349

  10. Authentication Procedures • One-way • Two-way • Three-way CSE 5349/7349

  11. Problems with PKI • Hierarchical model of trust • Chain of partial trust ending in one “fully trusted” entity • Identifier associated with the key pair • Unique distinguished name within the namespace • Private-key insecurity • Has to protect the private key • Technical and Implementation difficulties • Assumption of global namespace • Difficulty in detecting key compromise • Inefficient revocation CSE 5349/7349

  12. PKI Problems (cont’d) • Limited assurance provided in reality • CA’s generally protected in case of failure • What certificate assure (usually) • A particular message was generated by an entity that had available to it a particular private key; and • CA that provided the certificate has, at some time in the past, had grounds for believing that that private key was associated with a particular entity. • CA that provided the certificate has, at some time in the past, had grounds for believing that the entity had some kind of right to use that identifier, or had used that identifier in the past; and • CA that provided the certificate has, at some time in the past, had grounds for believing that the entity had access to the appropriate private key. CSE 5349/7349

  13. Problems (cont’d) • What it does not ensure • Private key was originally available to other entities as well as the entity to which it purports to be 'bound'; • Private key is now available to other entities as well as the entity to which it purports to be 'bound'; • Private key invocation that gave rise to a particular message was performed by the entity; and • Private key invocation that gave rise to a particular message was performed with the entity's free and informed consent. • Privacy invasiveness • Just to talk to your buddy securely, you may need to tell your life story to a third party! • Idiosyncrasy: • In order to have trust in the party you are transacting with, you are expected to have trust in organizations you have no relationship with at all CSE 5349/7349

  14. What is Really Needed! • Minimal Use of Identifiers • Minimal Registration Requirements • Mechanisms for Persistent Anonymity • Value Authentication without Identity • Attribute Authentication without Identity • Recourse in case of violation CSE 5349/7349

  15. Alternatives to PKI • Web of trust like in PGP • Simple Distributed PKI (SDPKI) • Login ID, password • Biometrics • Other form of cetificates CSE 5349/7349

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