I honestly think, as a community, we’re being far too dogmatic about our advice here, and we should recognise that there is value in learning things by example, and that more people having a better understanding of crypto is generally a Good Thing.
Using it in production, of course, is an entirely different matter, but that’s not what I’m contesting.
The way where people think they learn cryptography by making their own implementation is, indeed, wrong. Cryptography is about ensuring specific requirements in the face of active adversaries.
Self-implemented crypto misses many well-known caveats, causing them to be easily breakable. As such, it is not reasonable to consider them as something that aims learn about ensuring security properties in the face of active adversaries... but then that effort is not actually teaching about crypto, which is exactly that.
This is also the reason that the established wisdom for learning cryptography is to learn to break systems first. Almost everyone can make a cryptographic system they cannot break. For most folks, that means little. For those skilled at breaking crypto, that carries weight.
It's akin to saying, "you're not allowed to build your own smoke detector because it will be unsafe!". Of course I know that, I want to understand the differences between a photoelectric and ionization smoke detector, how they work in practice, because reading some PDF schematics just doesn't cut it for me.
I honestly don't understand the line of reasoning of all this crypto gatekeeping.
Fun fact: while I was doing my crypto deep dive in 2015, my language of choice being Haskell, I found issues in several libraries, specifically around entropy, and even one library with modulo bias [1]. They were acknowledged and addressed. It was a super fun learning exercise, and seeing all these comments how it's supposedly almost illegal to do this misses the point of people exploring and learning in their own ways.
https://github.com/vincenthz/hs-crypto-numbers/commit/bceb54...
This is exactly what the other people in this thread mean when they say "learn by breaking other crypto", assuming you didn't write those libraries.
It’s all about intent: my intent is understanding “how does this work?”, “how do I do this the right way?”, not breaking, and that’s how I found these things.
I don’t care about breaking stuff, it’s just not appealing to me. My whole frustration with this discussion is that for some reason, my intentions are not the True Way of the Crypto Experts, and then I’m not allowed to proceed.
It’s such utter nonsense, and this whole discussion made me realise the situation is actually worse than I thought. If these commenters here are representative of the wider crypto community, they’re really a bunch of elitist gatekeepers that cannot understand the difference between being the NSA and a mere mortal trying to learn things in their own way.
On a related note, Beldin here just contributed a new entry into cryptopals: the Gatekeeper hash, but only certain people can see the link.
Just about worst thing these absurd rules achieve is that effectively only rule breakers are allowed in.
I see the same problems in internet debates about which programming language to learn first or how to learn programming in general, and a lot of it just doesn’t take into account that learning is a long journey and staying on the path is often more important than taking the fastest or cleanest path. If trying to roll your own stuff is more engaging, great!
No, its not absurd.
Sure, I agree, for many things in life you can "learn by doing".
But this is cryptography.
There is no escaping that cryptography IS mathematics and an algorithm built on top of that mathematics.
Unfortunately the only way to learn the theory is by reading and understanding books or academic papers.
Otherwise you are just taking shortcuts based on a summary that someone else has written for you on a short blog or forum post. Which, aside from the fact that you are skipping the detail and hence not really learning, also brings us into the region of trust...
If you have no interest in learning the dry theory behind the cryptography, then you have no business rolling your own crypto. Because if you are not willing to understand the theory then you are going to make serious mistakes.
As someone who wholeheartedly buys into the “thou shalt not roll thine own crypto” mantra, this attitude is just sad. Everyone who wants to has all the business rolling their own crypto for learning purposes, and you have no business telling them they shouldn’t. Stifling this sort of exploration is fundamentally wrong.
First thing this mantra does is that we collectively know less a out crypto and security. Second thing it does is that it selects stick-in-ass rule followers away which is exactly contraproductive. And third, it makes us stuck with crappy convoluted code crypto libs had twenty years ago, cause supply of people capable to improve it is not build up.
I'm very confused. OP was suggesting to roll your own crypto as a learning exercise. What possible consequences could there be? Let alone "murky" ones?
Will your RSA implementation summon an eldritch monster or something?
It isn't enough to say "you'll never get it right for production, please use a framework or library for production". You simply don't want them to even experiment on their own.
I agree with saying "the most effective way to learn cryptography is through books and tools X, Y, Z". But one would imagine that writing a poor hashing algo would open up a door to alternate dimensions by how superstitious some are about it on this site.
The purpose of this is to learn how AES works, not to write a library you would actually use.
No. If you want to "learn from it", the first thing you should do is buy a copy of Bruce Schneier's Applied Cryptography.
Just reading (and fully understanding !) that book will alone put you in a position where you already know more about cryptography than 90% of other people.
If after that you still want to play around with rolling your own crypto, then fine, go for it. But be aware you are very much making your own bed and should be prepared to lie in the inevitable mucky consequences.
For the rest of us, frankly, no matter what your choice of programming language is, there will be at least one if not many more well respected long-established crypto libraries. Most people should just do themselves a favour and just use those libraries.
As the saying goes ... crypto is hard. A tiny, easily overlooked, mistake in your crypto code can have major consequences.