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Comment by ReidZB | Hacker News Reader

Well, it doesn't matter if Cryptol is compiled down to "safe" machine code, like FaCT, right? But that's not something I've seen explicitly stated in the Cryptol docs, so I would not make that assumption myself.

Are SAW or CompCert able to do formal verification around things like ensuring no branching on secrets, ensuring that memory is cleared after use, ...? Or does Cryptol make guarantees about the machine code it generates?

I see that SAW is able to do things like prove that hand-written, optimized code is equivalent to the Cryptol specification, which is certainly very neat - but that does not preclude potential side-channel vulnerabilities in the hand-written, optimized variant. After all, much of the scariness of side-channel attacks is that they're explicitly not targeting the (highly analyzed) mathematics of a construction, but rather its implementation.

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"Well, it doesn't matter if Cryptol is compiled down to "safe" machine code, like FaCT, right?"

It does. It gets you the correct implementation of crypto. Most failures are implementation errors. From there, before the buzz about constant-time, high-assurance security was just mitigating that stuff by using fixed-size, fixed-timing transmission of messages. As in, they couldn't tell anything about the inside of the black box because all they saw was the same behavior on the outside. Designers sacrificed some performance and plenty of bandwidth to do that. Tightly-coupled designed with no covert channel analysis or mitigation later showed up that leaked all sorts of stuff with them changing coding styles instead of bad architecture. That's when we need stuff like OP article and FaCT.

"Are SAW or CompCert able to do formal verification" (you)

"I can't remember if it addresses constant-time programming. So, I went looking arount, found the other language, and maybe someone will merge them. " (me)

I already answered that. I collected papers like FaCT specifically in case anyone wants to integrate them with Cryptol to address that gap if it exists. Also, other analysis and testing for information-flow security to make sure it is working on top of human review. This is a tiny part of my research given covert channel detection is mostly a solved problem with public, free methods such as Kemmerer's Shared Resource Matrix and Wray's for timing channels that most people just don't apply. Most of my research is on stuff that blocks code injection.

Ah, sorry, I didn't mean to imply that Cryptol itself doesn't matter. It does seem very useful for its intended purpose (though again this is from an outsider's perspective).

Rather, I meant to say that you do still need to worry about what sort of code Cryptol generates if you want to address the points raised in the original article (e.g. clearing secret memory). That was my original point, anyway: Cryptol doesn't address low-level side-channel problems.

As far as integrating FaCT and Cryptol, couldn't you use Cryptol to build the reference version of a construction, then implement a fast and side-channel-resistant variant in FaCT, then use SAW to prove the two were equivalent? (Maybe not as ideal as combining the two languages, exactly, but workable.)

I really appreciate you taking the time to reply. This stuff isn't my area of expertise, obviously, but I still find it very interesting.

Ok, yeah, we're on same page now. Far as Cryptol, I wanted to seeif it could be extended to generate FaCT which generated constant-time code. It would also generate C to check with SAW or other tools for extra checking or situations where side channels didn't matter. Could also be a tool that checked equivalence of the two at source or object code level so any checking of C code applied to FaCT.

That should cover most of the problem areas. I still think C itself or SPARK Ada could be modified to do what FaCT does. Some subset at least. Then, one can eliminate need to build FaCT-based tooling. So, those were the ideas I was brainstorming at least for what applies directly to those languages.

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