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Provable Security: Some Caveats

Provable security offers a theoretical foundation for cryptographic systems, yet significant caveats exist. This discussion explores key issues such as the difference between worst-case and average-case security, the reliability of proofs, and the potential pitfalls that come with an overemphasis on provable methods. As threats evolve, practical security measures, including expert testing and simple algorithms, remain crucial. The analysis highlights how distractions from underlying vulnerabilities can weaken overall system effectiveness. A balanced approach between theoretical proof and empirical validation is essential for robust security.

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Provable Security: Some Caveats

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  1. Provable Security: Some Caveats Ari Juels RSA Laboratories 3 November 1999

  2. What is provable security?

  3. Is this provable security? Ivan Damgård: Payment Systems and Credential Mechanisms with Provable Security Against Abuse by Individuals. 328-335 -- CRYPTO ‘88

  4. Or this follow-on? Birgit Pfitzmann, Michael Waidner: How to Break and Repair a "Provably Secure" Untraceable Payment System. 338-350 , CRYPTO ‘91

  5. Is this provable security? M. Ajtai and C. Dwork. A public-key cryptosystem with worst-case/ average-case equivalence. In Proc. 29th ACM STOC, pp. 284-293, 1997

  6. A follow-on P. Nguyen and J. Stern. Cryptanalysis of the Ajtai-Dwork Cryptosystem Proc. Of Crypto 98, pp. 223-242

  7. Problems with provable security • Who shall guard the guardians? Who’s to say that a proof is correct? • Worst case security  Average case security • Asymptotic security  Real world security

  8. But even with a more precise notion of ‘‘provable security’’...

  9. Amdahl’s Law Part 1 Part 2 Part 3 Part 4

  10. Amdahl’s Law Part 1 Part 2 Part 3 Part 4 …Accelerating a small piece doesn’t help much

  11. “Amdahl’s Law of Security” Crypto Part 1 Part 2 Part 3 Part 4

  12. “Amdahl’s Law of Security” Part 1 Part 2 Part 3 Part 4 …Strengthening secure part doesn’t help much

  13. Provable Security Strengthens Most Secure Part As far as we know, cryptography is rarely weakest point in system. Instead, it’s: • Bad password selection • Social engineering • Bad software implementation

  14. Where do you wnt to go today?re W A major security problem... Where do you want to go today?

  15. Provable security • May distract from more critical vulnerabilities • Hackers just go around the crypto • May yield more complex algorithms, and therefore make correct implementation less likely • Slow down implementations and encourage avoidance of crypto

  16. What lessons to be learned? • Emphasis on extensive expert and empirical testing as a basis for security as with, e.g., RSA • Can be in addition to proofs • Emphasis on simple proofs and algorithms and on ‘exact security’

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