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

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

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 Why Weak Authentication?

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 Technique Categories (1/2)

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

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

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 Technique Analysis

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

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 Summary