Hacker News Reader

Comment by RyanZAG | Hacker News Reader

"Every time I write something that involves some crypto I get absolutely terrified of what I'm likely to mess up."

Good!

" For that reason I almost always use an existing system or protocol."

Excellent! If only every was like you we wouldn't have these problems.

The key to understanding this is to understand that cryptography is not 'writing some crypto code'. No part of cryptography has anything to do with the code. Cryptography is about math - feel free to do some cryptography math and work on a mathematical algorithm. Once you have a perfect algorithm that has been peer reviewed, then you can transcribe that mathematical algorithm into code.

Failing to understand the math first means you have already failed and simply should not have even begun.

Cryptography: math first, code later. Failure to follow this sequence means you will be ridiculed and any excuse is simply not good enough.

View on HN

I agree in general, but you are painting with too broad strokes here:

> No part of cryptography has anything to do with the code.

There have been successful attacks against cryptography based on attacking the implementation. For example if two code paths take different time to execute, it is possible that this leaks information.

This is another reason why you should use a well honed library implementation of cryptography, for example OpenSSL.

This does of course not imply that the crypto–the maths of it–is broken. One just needs to be aware that it is not, in fact, sufficient to implement the maths correctly.

You're correct, and I think that means I'm painting my strokes not broad enough. After you get your math peer reviewed, you then need to get your implementation of the math peer reviewed as well - likely by a low-level hardware engineer and not just some web developers.

Generally, however, nearly all failures of security come from misunderstanding the math when creating the implementation. So I'd say that at least ensuring anybody writing crypto has a completely understanding of the crypto math before touching the code is a very good first step in getting somewhere.

Thank you for being the voice of reason. It's so easy to get confused, too, because "crypto code" is indistinguishable from "other code", but the implications are much greater. You don't need to peer review a IRC library, but you _need_ to peer review cryptography.

That's just how it is, and if I had to highlight one sentence from your comment it would be "Failing to understand the math first means you have already failed and simply should not have even begun."

I wish people would understand this instead of thinking trial and error works for cryptography. I mean, heck, most of us learned to code through trial and error, and I can understand why people think they can learn cryptography the same way, but that is not true, and a very toxic mindset.

So what's the preferred route for an opensource project?

# TODO add crypto

# TODO get someone to review the crypto later

You could use a well established library. GPG or OpenSSL for example.

OpenSSL is fairly low level and still lets you shoot yourself in the foot. You can make the same mistakes as in the OP post.

Reply on news.ycombinator.com