Weak Authentication: How to Authenticate Unknown Principals without Trusted Parties

1. Weak Authentication: How to Authenticate Unknown Principals without Trusted Parties Jari Arkko & Pekka Nikander Presented by Riku Honkanen

2. Presentation Outline • ”Cryptographically strong authentication between previously unknown parties without relying on trusted third parties” • Why weak authentication? • Weak authentication techniques • Classification • Concrete techniques • Technique Analysis • Economic impacts & probabilities

3. Why Weak Authentication? • If there are no real-world identities/effects • Imperfect security is sometimes enough • Higher cost of strong authentication • Current & potential applications: • Personal area networks • Secure Shell (SSH) • Session Initiation Protocol (SIP) • Multi-homing • Mobilitity

4. Technique Categories (1/2) • Spatial Separation • Ensuring that the peer is on a certain path • Temporal Separation • Peers relate past & current communications • Asymmetric Costs • Cost of attack is higher than cost of defense • Application Semantics • Cryptographic properties of identifiers

5. Technique Categories (2/2) • Combined and Transitive Techniques • The mentioned categories can be combined for improved security • Time and location as main dimensions Same peer, different location Time Same peer One time use Over a specific path Location

6. Concrete Techniques • Anonymous Encryption - temporal • e.g. unauthenticated Diffie-Hellman secures a single session • Challenge-Response - spatial • Freshness and peer on a certain path • Leap-of-Faith – temporal, spatial, asymmetric cost • Unauthenticated at start of first connection • Following connections authenticated • Cryptographically Generated Addresses – spatial & application • Opportunistic IPSec

7. Technique Analysis • Anonymous Encryption • Vulnurable for man-in-the-middle attack in the beginning of the session • Benefits community more than a single user • Challenge-Response • Probability of a certain path having an attacker • Leap-of-Faith • Uncertainty gets smaller when number of connections increases between specific peers

8. Economic Impacts & Probabilities • Cost of attack vs. cost of defense • Weak authentication may be enough to raise the cost of the attack to multiples of cost of the defense • Probability of the attack • Weak authentication may lower the probability of an attacker being present significantly • Economics and probabilities should be understood before application protocol design

9. Summary • Weak authentication is good enough for some applications • Basic WA techniques can provide significant advantage with low cost • Importance of uncertainty, probability and economic impact analysis • the results may be surprising