PORTCULLIS: PROTECTING CONNECTION SETUP

FROM DENIAL-OF-CAPABILITY ATTACKS

Presenter: Chen Chih-Ming

96/12/27

Outline

Background Problem Definition State of Art Portcullis Architecture Designs Potential Attacks Evaluation Discussion Conclusion

Background

DoSProtected by Capability-based System

Capability-based System DoC

Flood request channel!

Problem Definition

Guarantee successfully transmitting

State of Art

Identity-Based FairnessPer-Source FairnessPer-Path Fairness (TVA)Per-Destination Fairness

Proof-of-Work SchemesPer-Bandwidth Fairness (Speak up)Per-Computation Fairness

Portcullis Architecture

Authenticity Availability Freshness Efficiency Granularity

Design

Design – cont.

p = H(x||r||hi||dest IP||l)r : 64 bit random choosed by clienthi :seed from DNSDest IP: Destination IPl : puzzle level, find the last l bits of p are all

zero

Theoretical Result

Assume attack have bounded resources Equal computation power M = Number of malicious machines Result

Legitimate clients succeed in time O(M)For any routing policy, the time needed for

capability setup is O(M)

Potential Attacks

Sharing Puzzle SolutionsAttack different linkStill cannot flood bottleneck

Timing AmplificationHigh level puzzle need more time.Low level puzzle can pass through.

Evaluation

Internet Scale Simulation Portcullis Attacker Strategies Comparative Simulations Partial Deployment

Evaluation – cont. Internet Scale Simulation

DAIDA Skitter probe result○ Router-level topology

Victim uses single link connect InternetNo bandwidth measurement

○ Sender have 1/10 bw of receiver(200Mbps)○ Others are 10x bw of receiver

Request packet is 1000 bitsRequest channel occupies 5% bwRandomly place clientEqual computational resources

Evaluation – cont.

Portcullis Attacker Strategies

Evaluation – cont.

Comparative SimulationsIP to ASN map router to AS for TVA

Evaluation – cont.

Partial DeploymentVictim’s ISP upgrades router.

Discussion

Asymmetric computation Power

Memory bound function, 3x~5x Puzzle Inflation

Not exhaustedExhausted by high level packetExhausted by mixture packet

Platform SHA-1 hashes/min Normalized

Nokia 6620 25k 1

Nokia N70 36k 1.33

Sharp Zaurus PDA 56k 2.24

Xeon 3.2GHz PC 956k 38.24

Conclusion

Portcullis can make capability-based system more robust against DoC.

Comment

Partial Deployment is strong advantage. Computing power varies dramatically

from platform to platform.

Bye