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Running Secure Server Software on Insecure Hardware Without Parachute

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In today’s world, you may not know if the hardware you are running software on is secure or not. How can you ensure that, regardless of the hardware security, the software stays protected? CloudFlare’s systems engineer, Nick Sullivan shares advanced techniques on how to protect your server software. These techniques include anti-reverse engineering methods, secure key management and designing a system for renewal.

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Running Secure Server Software on Insecure Hardware Without Parachute

  1. 1. Nicholas Sullivan Systems Engineer
 @grittygrease Running Secure Server Software on Insecure Hardware without a Parachute
  2. 2. What this talk is about u The web is changing — consolidation at the edge u Fundamental assumptions about server security are wrong u How do we design server software with the worst case in mind? u Distinguish between long and short term secrets u Devise approaches for protecting each 2
  3. 3. Let’s Talk About Web Infrastructure
  4. 4. 4
  5. 5. Global Website Traffic 5
  6. 6. Global Website Traffic with CDN 6
  7. 7. Current Map 7
  8. 8. Future Map 8
  9. 9. Future Map 9
  10. 10. Edge Computing Threat Model
  11. 11. Traditional server threat model u Assume server is secure u Add layers of protection to keep attackers out u Network layer protection u Operating System Level: principle of least privilege u Protection against maliciously installed code u More advanced barriers 11
  12. 12. Globally distributed servers u Less jurisdictional control = less physical security u Physical access trumps static defense layers ! u Traditional defenses helpful, but not ideal u Cannot rely on security of keys u Single break-in results in immediate compromise 12
  13. 13. A More Effective Approach
  14. 14. Approach system security the ‘DRM way’ u Assume attacker has bypassed all static defenses u Goal is to refresh secrets before they are compromised u Split system into long-term secrets and short-term secrets u Focus on renewability of secrets 14
  15. 15. Secrets must be split into two tiers u Long-term Secrets u Useful for attacker for long period of time u Do not store at the edge ! u Short-term Secrets u Expire after a short period of time u Cannot be re-used 15
  16. 16. Example: Traditional TLS termination u TLS handshake with nginx and Apache u SSL keys on disk u Read from disk, use in memory ! u Cryptographic elements at risk if server is compromised u Private key u Session key 16
  17. 17. TLS revisited for untrusted hardware u Long term secrets u Private key ! u Short term secrets u Session key u Session IDs and Session ticket keys u Credentials to access private keys 17
  18. 18. How to Protect 
 Short-term Secrets
  19. 19. Short-term secrets — threat model u Must live on machines in unsafe locations u Memory u Control Flow u By the time a secret is broken, it should be expired u Don’t keep secrets in a useable state u Impose computational cost to retrieve the original secret u Expire secrets quickly ! 19
  20. 20. Techniques from DRM are applicable u White-box cryptography u Code obfuscation 20
  21. 21. Standard Cryptography Threat Model 21 Alice Bob Eve
  22. 22. White-box Cryptography Threat Model 22 Alice Bob Eve
  23. 23. White-box Cryptography Threat Model 23 Aleve Bob
  24. 24. White-box cryptography u Hide the cryptographic key from everyone u Protect against key extraction in the strongest threat model ! u Takes time to extract key — lots of math u Choose difficulty based on secret lifetime 24
  25. 25. White-box cryptography implementations 25 u Commercial products u Irdeto, Arxan, SafeNet, etc. u Open source u OpenWhiteBox
  26. 26. Code obfuscation 26
  27. 27. Code obfuscation u Making reverse engineering difficult u Compile-time control-flow modification u Data transformation in memory u Anti-debugging 27
  28. 28. Before 28
  29. 29. After 29
  30. 30. Code obfuscation implementations u Commercial products u Arxan, Irdeto, etc. u Open source u Obfuscator-LLVM 30
  31. 31. Long-term Secrets
  32. 32. Keyless SSL u SSL without keys? Surely you’re joking. u SSL without keys at the edge. That’s better. 32
  33. 33. How Keyless SSL Works u Split the TLS state machine geographically u Perform private key operation at site owner’s facility (in HSM, etc) u Perform rest of handshake at edge u Communicate with signing server over mutually authenticated TLS 33
  34. 34. Keyless SSL Diagram 34
  35. 35. 35
  36. 36. Conclusion
  37. 37. Conclusion u Untrusted hardware requires a new approach u Split secrets into long-term and short-term u Design for rapid renewal — replace secrets faster than they can be broken u Leverage short-term secrets to access long-term secrets 37