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Comment by ktta | Hacker News Reader

I've always seen 'rolling your own crypto' as not being recommendation against writing your own library, but creating your own primitive.

Sure, writing your own library is very difficult, but you have a simpler set of problems, which proper testing, another set of eyes and enough tools will take care of the big problems.

Now, implementing your own primitive and recommending to use it is bad. For a primitive to be deemed secure, it has to undergo years of review and testing by seasoned cryptographers.

This isn't a recommendation to write your own library, but my opinion that it is okay to do so if you want something that none of the major libraries offer.

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Even just using crypto primitives is dangerous unless you've got experience. There's an old post from matasano about it https://www.nccgroup.trust/us/about-us/newsroom-and-events/b...

Every line of code written can be a severe vulnerability, not just code dealing with crypto. In case of crypto, being well-informed is good enough to not mess up those kind of implementations (on a theoretical level). The problems mentioned can be pointed out and verified on paper. But you can't say the same thing for code.

No, you can write crypto code, even when knowing stuff about the crypto, and still mess up. Crypto is problematic because you often cannot easily check whether you're wrong (it could be a tiny edge case that isn't tested because your input space is huge).

I didn't deny messing up crypto code is a thing. I'm saying messing up code is a separate problem from messing up how one architects projects using crypto.

What you say as messing up with edge cases, etc. is a programming problem. The errors talked about in the link he posted is about using faulty crypto. Today it is common knowledge to never use ECB.

What cipher mode you use is a problem you think about before you even start writing a single line of code. But you are talking about programming errors, which one can make in all areas, not only ones involving crypto. Those errors can break security similar to messing up crypto implementation.

I strongly disagree with this sort of attitude. It scares people away from learning how cryptography works. We should be encouraging everyone to write their own crypto: it's a fantastic learning experience. Just don't use your first go in production.

I disagree. The way you get experience is by trying things. If everyone followed that advice then nobody would learn anything.

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