1. Public Key Infrastructure
Jonathan Baulch

2. Public Key Infrastructure
Introduction
Digital Certificates
Web of Trust
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3. Introduction
Security architecture to increase the level of confidence when passing information
Multiple meanings
Methods, technologies, and techniques to provide a secure infrastructure
Use of a public and private key pair for authentication and proof of content

4. Introduction Expected benefits of Public Key Infrastructure (PKI)
Certainty of the quality of information sent and received electronically
Certainty of the source and destination of that information
Assurance of the time and timing of that information
Certainty of the privacy of that information
Assurance that the information may be introduced as evidence in a court of law

5. Components of PKI Certification Authority Revocation
Registration Authority
Certificate Publishing Methods
Certificate Management System
PKI ‘aware’ applications

6. Diffie-Hellman Protocol
Developed by Diffie and Hellman in 1976
Published in ground-breaking paper “New Directions in Cryptography
Allows two users to exchange a secret key over an unsecure channel without any prior secrets

7. Diffie-Hellman Protocol
Uses a prime number p and parameter g (g < p) with the following property
For every number n between 1 and p-1 inclusive, there is a power k of g such that n = gk mod p
Alice and Bob agree on a p and g
Each pick a secret number
Each send the value A/B of gsecret number mod p
Each then compute A/Bsecret number mod p
Alice and Bob will then have the same value

8. Digital Certificates Four types of certificates Personal certificates
Server certificates
Software publisher certificates
Certificate authority certificates

9. X.509 Standard
Defines what information can go into a certificate and how to write it down
All X.509 certificates contain
Version
Serial Number
Signature Algorithm Identifier
Issuer Name
Validity Period
Subject Name
Subject Public Key Information

10. Web of Trust
Concept used in PGP, GnuPGP, and other Open PGP compatible systems to establish authenticity of public key and its owner
Decentralized model
Any user can be a part of, and a link between, multiple webs
Developed by Phillip Zimmermann in 1992

11. Pretty Good Privacy
Uses a combination of public key and symmetric encryption
Serial combination of hashing, data compression, symmetric key cryptography, and public key cryptography
Each public key is bound to a user name or
Created to contrast the X.509 system of a hierarchal approach based on certificate authority

12. Problems with PGP
Users who lose the private key can no longer decrypt messages
Without central controller, web of trust depends on other users for trust
Those with new certificates will not be readily trusted by other users’ systems
Possible that a new user could not find anyone else to endorse a new certificate