Chain of Fools: An Exploration of Certificate Chain Validation Mishaps
summary
Paper argues poor crypto APIs and bad online advice let implementers accept attacker-supplied intermediates, demonstrating misuse in PI OpenSSL x.509 store code patterns. Analysis of ~24k apps finds ~4% (naive) rising to 7.1% of apps via LibScout using Android SafetyNet, with ~87% still on older libraries. Builds include a Flask server showing the incorrect validation, a Python rogue-CA generator and a mitm proxy add-on that forges JWS attestations — the forgery succeeds against the flawed validation.
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chapters (41)
- 0:00Introduction and agenda
- 0:44Research topics
- 1:33The difficulty of validation
- 1:55The developer experience
- 2:51X.509 certificate basics
- 3:05Trust anchors and certificates
- 4:32Validation requirements
- 5:43When developers should validate
- 6:10Real-world use cases
- 6:34Safety Net API overview
- 7:05How safety net works
- 8:23JSON Web Signatures
- 9:26JWS structure and usage
- 10:06Safety Net attestation payload
- 10:54Developer documentation issues
- 11:27X5C header in safety net
- 12:03Cryptographic libraries analysis
- 12:30PyOpenSSL and X509 Store
- 12:46Incorrect validation patterns
- 14:38Why insecure patterns occur
- 16:04Fixing the libraries
- 16:25Correct validation approach
- 17:20Summary of best practices
- 18:26Misuse resistant primitives
- 18:52Safety Net usage analysis
- 20:11Data acquisition
- 21:20Analysis results
- 21:36Limitations of static analysis
- 22:57Advanced library detection
- 23:18Refined analysis results
- 29:53Open source tool release
- 30:03Forging Safety Net data
- 35:20Tooling demonstration
- 35:58Demo analysis
- 36:13Conclusion and final points
- 37:31Security champions
- 37:46Validation alternatives
- 38:09Session wrap-up
- 38:47Q&A session start
- 40:01Library support
- 41:03TLS and Safety Net
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