Cryptographic Protocols

1
Cryptographic Protocols

• Cryptographic Protocols
• A sequence of messages intended to achieve some
  security goal.
• Informal analysis and design of CP is error prone
  
• Properties are subtle
• Protocols run in an hostile environment
• Powerful intruder
• Concurrent runs
• Needham-Schroeder Protocol (Example)
• Published in 1978.
• Formal Methods used to discover flaw in 1995.

2
Formal Analysis of Cryptographic Protocols

• Dolev-Yao Intruder
• Complete control over channel
• Can read, alter, destroy any message
• Can do everything, an honest principal can do
• Dolev-Yao Problem
• Given a cryptographic protocol,
• Specify its goals
• Prove correctness or provide counter-examples
  highlighting its failure
• Assuming underlying cryptosystem is perfect.
• Existing Formal Mechanisms
• Proof Generation Mechanisms
• Use Theorem Proving Techniques
• Attack Construction Mechanisms
• Use Model Checking

3
CryPA Our Tool

• Cryptographic Protocol Analyzer
• Based on Strand Spaces Formalism
• GUI Specification of cryptographic protocols
• Generation of PVS Theories, which axiomatize -
• Cryptographic Operations
• Intruder Capabilities
• Message Exchange
• Protocol Goals and Assumptions
• Proofs of Protocol Properties
• Construction of Attacks on Protocols

GUI
CAPSL
CryPA
PVS Connector
Attack Constructor