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> Well, sure, if your start with those premises, then I'm not surprised that you reach the conclusion that the goal is unachievable. I didn't say unachievable.

> Well, sure, if your start with those premises, then I'm not surprised that you reach the conclusion that the goal is unachievable. I didn't say unachievable. I said costly. > First of all, if constructing a formal specification for PKIX is not possible, then that should be telling you that it either needs to be simplified, better specified or scrapped altogether for something better (the latter would require an extremely large transition period, I'm imagining, so the first two are much preferred in this situation). https://xkcd.com/927/ https://xkcd.com/927/ The specs for the new thing would basically have to be written in Coq or similar. Even if you try real hard to keep it small and not make the... many mistakes made in PKIX's history... it would still be huge. And it would be even less accessible than PKIX already is. > For example, you could verify that your function that verifies a CA certificate, when passed the STRICT flag, is really more strict than when not passed the STRICT flag. That's just an argument for better testing. That's not implementation verification. > This would eliminate the first bug in this security advisory and all other similar bugs in the same function call-chain. Only if you thought to write that test to begin with. Writing a test for everything is... not really possible. SQLite3, one of the most tested codebases in the world, has a private testsuite that gets 100% branch coverage, and even that is not the same as testing every possible combination of branches. > BTW, what I just said is really easy to specify, and I'm guessing it's also very easy to prove, since I'm guessing that the strict checks are just additional checks, while the normal checks are shared between the two verification modes. It's not. The reason the strictness flag was added was that OpenSSL was historically less strict than the spec demanded. It turns out that when you're dealing with more than 30 years of history, you get kinks in the works. It wouldn't be different for whatever thing replaces PKIX. > I think the problem is also that OpenSSL devs, like the vast majority of devs, probably have no desire/intention/motivation/ability to do formal verification, otherwise you could even do this in the OpenSSL code base itself [...] You must be very popular at parties. > I'm also guessing that your budget estimate is an exaggeration since miTLS and EverCrypt, [...] Looking at miTLS, it only claims to be an implementation of TLS, not PKIX. Not surprising. EverCrypt is a cryptography library, not a PKIX library.

wizeman 6y ago
> That's just an argument for better testing. That's not implementation verification. No, I'm not talking about testing, I'm talking about really basic formal verification: forall (x: Certificate), verify_certificate(x, flags = 0) == invalid ==> verify_certificate(x, flags = STRICT) == invalid This is trivial to specify and almost as trivial to prove to be correct for all inputs. Testing can't do that, no matter how good your testing. > Only if you thought to write that test to begin with. Writing a test for everything is... not really possible. I agree, but I'm not talking about testing. I'm talking about formal verification. > It's not. The reason the strictness flag was added was that OpenSSL was historically less strict than the spec demanded. It turns out that when you're dealing with more than 30 years of history, you get kinks in the works. It wouldn't be different for whatever thing replaces PKIX. That's totally fine and wouldn't affect the verification of that function at all. This is a very simple property to verify and it would avoid this bug and all similar bugs in that function (even if that function calls other functions, no matter how large or complex they are). Other functions also have such easy to verify properties, this is not hard at all to come up with (although sure, some more difficult properties might be harder to verify). > You must be very popular at parties. I didn't want to be dismissive of OpenSSL devs or other devs in general, I just find it frustrating that there are so many myths surrounding this topic, and a lot less education, interest and investment than I think there should be, nowadays.
- cryptonector 6y ago
  You are confusing verification as in "certificate" with verification as in "theorem proving", and you are still assuming a formal description of what to verify (which I'll remind you: doesn't exist). And then you go on to talk about myths and uneducated and uninterested devs. Your approach is like tilting at windmills, and will achieve exactly as much.
  - wizeman 6y ago
    If I understood you correctly, then I am not confusing those two things. Maybe you haven't noticed but I actually wrote a theorem about a hypothetical verify_certificate() function in my previous comment. Maybe you also haven't noticed, but I didn't need a formal description of how certificate validation needs to be done to write that theorem. And I assure you, if the implementation of verify_certificate() is anything except absolute garbage, it would be very easy to prove the theorem to be correct. I actually have some experience doing this, you know? I'm not just parroting something I read, I've proved code to be 100% correct multiple times using formal verification (i.e. theorem proving) tools. That is, according to certain basic and reasonable assumptions, of course, like e.g. the hardware is not faulty or buggy while running the code, and that the compiler itself is not buggy, which would be a lot more rare than a bug in my code -- and even then, note that compilers and CPUs can be (and have been) formally verified. Maybe you don't agree with my approach but I think it's the most realistic one for a project such as this and I am absolutely confident it would be practical, would completely eliminate most (i.e. more than 50%, at least) existing bugs with minimal verification effort (which almost anyone would be capable of doing with minimal training), and would steadily become more and more bug-free with additional, incremental verification (i.e. theorem proving) and refactoring effort.

wizeman 6y ago

> That's just an argument for better testing. That's not implementation verification. No, I'm not talking about testing, I'm talking about really basic formal verification: forall (x: Certificate), verify_certificate(x, flags = 0) == invalid ==> verify_certificate(x, flags = STRICT) == invalid This is trivial to specify and almost as trivial to prove to be correct for all inputs. Testing can't do that, no matter how good your testing. > Only if you thought to write that test to begin with. Writing a test for everything is... not really possible. I agree, but I'm not talking about testing. I'm talking about formal verification. > It's not. The reason the strictness flag was added was that OpenSSL was historically less strict than the spec demanded. It turns out that when you're dealing with more than 30 years of history, you get kinks in the works. It wouldn't be different for whatever thing replaces PKIX. That's totally fine and wouldn't affect the verification of that function at all. This is a very simple property to verify and it would avoid this bug and all similar bugs in that function (even if that function calls other functions, no matter how large or complex they are). Other functions also have such easy to verify properties, this is not hard at all to come up with (although sure, some more difficult properties might be harder to verify). > You must be very popular at parties. I didn't want to be dismissive of OpenSSL devs or other devs in general, I just find it frustrating that there are so many myths surrounding this topic, and a lot less education, interest and investment than I think there should be, nowadays.

cryptonector 6y ago
You are confusing verification as in "certificate" with verification as in "theorem proving", and you are still assuming a formal description of what to verify (which I'll remind you: doesn't exist). And then you go on to talk about myths and uneducated and uninterested devs. Your approach is like tilting at windmills, and will achieve exactly as much.
- wizeman 6y ago
  If I understood you correctly, then I am not confusing those two things. Maybe you haven't noticed but I actually wrote a theorem about a hypothetical verify_certificate() function in my previous comment. Maybe you also haven't noticed, but I didn't need a formal description of how certificate validation needs to be done to write that theorem. And I assure you, if the implementation of verify_certificate() is anything except absolute garbage, it would be very easy to prove the theorem to be correct. I actually have some experience doing this, you know? I'm not just parroting something I read, I've proved code to be 100% correct multiple times using formal verification (i.e. theorem proving) tools. That is, according to certain basic and reasonable assumptions, of course, like e.g. the hardware is not faulty or buggy while running the code, and that the compiler itself is not buggy, which would be a lot more rare than a bug in my code -- and even then, note that compilers and CPUs can be (and have been) formally verified. Maybe you don't agree with my approach but I think it's the most realistic one for a project such as this and I am absolutely confident it would be practical, would completely eliminate most (i.e. more than 50%, at least) existing bugs with minimal verification effort (which almost anyone would be capable of doing with minimal training), and would steadily become more and more bug-free with additional, incremental verification (i.e. theorem proving) and refactoring effort.