These were initially created by a small group inside of Matasano, which ended up growing into the Cryptography Services of NCC Group.

I've used these challenges in a few different contexts, they're great.

I taught myself rust by implementing solutions to these challenges, and I taught a CS class in which I had students improve their C language skills by implementing solutions to these challenges. Students got some crypto knowledge on the side!

I also learned Rust by completing (the first couple of sets of) these challenges. It was fan-damn-tastic. Way, way better than Project Euler, or reimplementing Yet Another Blog Engine or whatever. I can't recommend them highly enough, and I learned some useful crypto too!

I used them to teach myself F# (or more accurately, to force myself to apply F#). Enjoyed the challenges and the learning (of both crypto and F#).

These kinds of comments really make my day. Thanks!

I'll start by echoing thenewwazoo's comment - I learnt Ruby on these challenges, and I would actually suggest the questions are better worded, more generally educational and generally laid out than most of Hacker Rank. For example, you're forced to write maintainable code, because your solution to one question ends up adapted to a later question.

I hit two different Ruby segfault conditions someone patched just so I could finish this challenge. You know you're deep in a language when that happens.

For anyone who finished Set 8: give yourself an exceptional pat on the back. I'm looking forward to revisiting this at a time when it hopefully goes more public.

Downsides: Extreme jadedness towards commercial encryption products and the people that peddle them.

My favorite quote from this is:

> How practical these attacks were. A lot of stuff that I knew was weak in principle (like re-using a nonce or using a timestamp as a 'random' seed) turns out to be crackable within seconds by an art major writing crappy Python.

It shows the realization that "somewhat broken" in crypto usually means horribly broken.

Favorite part:

"One final observation. Crypto is like catnip for programmers. It is hard to keep us away from it, because it's challenging and fun to play with. And programmers respond very badly to the insinuation that they're not clever enough to do something. We see the F-16 just sitting there, keys in the ignition, no one watching, lights blinking, ladder extended. And some infosec nerd is telling us we're can't climb in there, even though we just want to taxi around a little and we've totally read the manual."

"You get the challenges in batches of eight by emailing cryptopals at Matasano, and solve them at your own pace, in the programming language of your choice. Once you finish a set, you send in the solutions and Sean unlocks the next eight. (Curiously, after the third set, Gmail started rejecting my tarball as malware.) "

The Challenges: Cryptopals --> http://cryptopals.com/

Can you still submit them for some kind of recognition? I know you can get them all now without emailing.

(FWIW I got stuck on getting an existing software package to get the correct result from encrypting via AES with a given key.)

Not really, but sort of. There's a set 8, and it's by far the best of all 8 sets (I'd rank the sets 8->6->2->3->4->7->5->1), but you have to mail Sean to get it, and you should tell him you've done at least sets 1-6.

I emailed them like 3 years ago and never heard anything. I doubt anyone monitors the mailbox anymore.

I haven't checked. Do you mean can you receive some sort of certificate of successful completion? I would think successful solutions with sharaebale code (e.g. a github repo) would be adequate for recognition of completion and competency.

I meant if they still care if you complete them.

And I thought they asked not to publish solutions?

Ah, I see. Well then, seems like it'd be good to ping them for some clarity and perhaps share the answer(s) here. :)

The nature of the challenges means you'll always know when you've solved them.

I worked through some of these[0] a while back as a way to learn property based testing in Python with Hypothesis[1]. Never finished them, but it was a fun exercise.

[0] https://github.com/avyfain/Cryptopals-Hypothesis [1] http://hypothesis.works

The thing I loved about these challenges, aside from extracting the 90s hip hop references from the ciphertext, was getting back to computing primitives.

I spend so much time in my day job dealing with high level abstractions and objects it's a good reminder about how important the 0 and 1s are.

And the challenges are very well written, if only all teaching materials could keep you engaged like these do.

Does anyone have a preference to which languages are the best to implement in, or is it more a case of what you're comfortable with?

I started the challenges in 2013 in Python, which I only have a very cursory knowledge of, so if there's an easier language to implement in (even if it's new to me), I would like to give it another go.

Python is the language most used by people who successfully finished all 6 sets, followed by Ruby, Java, and Go. Ruby and Python are both good because they have sane byte strings and automatically promote fixnums to bignums.

<shameless plug>

If you enjoy these challenges you might want to join my team at Google, to analyze, break, design and implement real-world crypto solutions for products used by billions of people.

Aside from short-term projects like analyzing and improving state-of-the-art password hashing or end-to-end encryption schemes, we've started two long-term that could use your help: Wycheproof [1] and Tink [2]. The former is a revolutionary testing framework that has discovered 40+ bugs [1] in many popular crypto libraries. The later provides a safe, simple, agile and fast way to accomplish common crypto tasks.

If this sounds exciting, please send your resumes to [email protected]. Cheers!

[1] https://github.com/google/wycheproof

[2] https://github.com/google/tink

[3] https://github.com/google/wycheproof/blob/master/doc/bugs.md

</shameless plug>

I'd point out that Thai here is one of the inspirations for the crypto challenges, but we already did on the front page. :)

This is a pretty amazing team, and if you're not familiar with it already, Tink is Thai and Daniel Bleichenbacher's team's answer to Nacl.

What if you were previously and recently rejected by Google?

Thanks for including "(blog post about completing them)" in the title.

Ironically, that's been removed by the mods.

There is a reason for that and it's because the mods take a hard line on editorializing the title of the submission. It's likely done automatically by a bot though.

from the guidelines[0]: Please don't do things to make titles stand out, like using uppercase or exclamation points, or adding a parenthetical remark saying how great an article is. It's implicit in submitting something that you think it's important. ... Otherwise please use the original title, unless it is misleading or linkbait.

0. https://news.ycombinator.com/newsguidelines.html

Indeed. In this case it is misleading simply to call it by the title "The Matasano Crypto Challenges". Specifically, this is a blog post about the Matasano Crypto Challenges.

The modification wasn't intended to make the title stand out, and it wasn't editorializing, it was deliberately adding information to help you, the reader, know what it was you were clicking through to.

I understand the reasons, but I feel that sometimes the mods revert titles without thinking, and without assessing why it might have been changed. Again, I understand the reasons, and having yet another time sink is perhaps unwelcome, but I'd like to see some way - like the "vouch" mechanism - where altered titles can be accepted.

(2013)