4 ms·

Top of the second page: https://link.springer.com/article/10.1007/s00165-012-0269-9 https://link.springer.com/article/10.1007/s00165-012-0269-9 My understandin

Top of the second page: https://link.springer.com/article/10.1007/s00165-012-0269-9 https://link.springer.com/article/10.1007/s00165-012-0269-9 My understanding is that both Needham–Schroeder and SSL had formal verification prior to the breaks, but the breaks relied on properties outside of what was proven (which was thought to be complete at the time).

MaxBarraclough 7y ago
Great, thanks. I found a freely available pre-print at http://alfredo.pironti.eu/research/sites/default/files/cf11.pdf http://alfredo.pironti.eu/research/sites/default/files/cf11.... The relevant content is mostly on page 2. They seem to be saying that when it comes to crypto, both the requirements work and the implementation work are both challenging and error-prone, even for expert practitioners. I don't think they're exactly saying anything against formal methods, though: > It is significant, for example, that the above mentioned flaw affecting the Needham-Schroeder public-key protocol could be found by applying formal methods Later, under Motivation, regarding what are essentially integration bugs: > in OpenSSL an error condition returned by a cryptographic function was incorrectly interpreted by the function caller, making the application accept corrupted data; such a fault cannot be found if a formal model that has no relation with the implementation code is analyzed Not exactly a demonstration of a weakness of formal methods. Instead, an instance of a bug (a normal one, not a side-channel vulnerability) occurring in a system which was only partially formally verified. > a large gap still exists between these models and a real-world protocol implementation and its execution. A problem with real-world implementation, not with formal methods. I wonder what they would have made of 'SPARKSkein', released around the time that paper was published. [0] I suppose it wouldn't have been anything all that new - integration bugs could still occur. [0] https://www.adacore.com/papers/sparkskein https://www.adacore.com/papers/sparkskein
- albntomat0 7y ago
  My takeaway is that using formal methods is difficult to turn into any sort of actual security guarantee, due to the difficulty of connecting them to a real world system in a meaningful way. While formal methods could produce something meaningful with proper "inputs", getting that done is hard.
  - MaxBarraclough 7y ago
    I'm more optimistic. There's real value in building ultra-low-defect crypto code, and as far as I can tell, formal methods have a good track-record there. We already knew that integration into non-verified code isn't guaranteed to be free of defects - that's out of scope by definition. That's somewhere safe languages can help though. What the paper describes as corrupted data might well be the kind of bug that often happens in C, but rarely happens in a safe language. The other question is vulnerability to side-channel attacks. Today's formal methods aren't much use against them.

MaxBarraclough 7y ago

Great, thanks. I found a freely available pre-print at http://alfredo.pironti.eu/research/sites/default/files/cf11.pdf http://alfredo.pironti.eu/research/sites/default/files/cf11.... The relevant content is mostly on page 2. They seem to be saying that when it comes to crypto, both the requirements work and the implementation work are both challenging and error-prone, even for expert practitioners. I don't think they're exactly saying anything against formal methods, though: > It is significant, for example, that the above mentioned flaw affecting the Needham-Schroeder public-key protocol could be found by applying formal methods Later, under Motivation, regarding what are essentially integration bugs: > in OpenSSL an error condition returned by a cryptographic function was incorrectly interpreted by the function caller, making the application accept corrupted data; such a fault cannot be found if a formal model that has no relation with the implementation code is analyzed Not exactly a demonstration of a weakness of formal methods. Instead, an instance of a bug (a normal one, not a side-channel vulnerability) occurring in a system which was only partially formally verified. > a large gap still exists between these models and a real-world protocol implementation and its execution. A problem with real-world implementation, not with formal methods. I wonder what they would have made of 'SPARKSkein', released around the time that paper was published. [0] I suppose it wouldn't have been anything all that new - integration bugs could still occur. [0] https://www.adacore.com/papers/sparkskein https://www.adacore.com/papers/sparkskein

albntomat0 7y ago
My takeaway is that using formal methods is difficult to turn into any sort of actual security guarantee, due to the difficulty of connecting them to a real world system in a meaningful way. While formal methods could produce something meaningful with proper "inputs", getting that done is hard.
- MaxBarraclough 7y ago
  I'm more optimistic. There's real value in building ultra-low-defect crypto code, and as far as I can tell, formal methods have a good track-record there. We already knew that integration into non-verified code isn't guaranteed to be free of defects - that's out of scope by definition. That's somewhere safe languages can help though. What the paper describes as corrupted data might well be the kind of bug that often happens in C, but rarely happens in a safe language. The other question is vulnerability to side-channel attacks. Today's formal methods aren't much use against them.