Stripe-CTF 3 Writeup • Hacker News Board

Re: Stripe-CTF 3 Writeup

#71

Post by isb » Fri, Jan 31, 2014, 11:51 AM UTC

darklajid wrote: post #52

I've got mixed feelings this time. Disclaimer out of the way: No sense of entitlement here, every time I see a challenge like this I expect to fail. I'm really, really happy that people (Stripe, here) offer their time and resources to entertain us. I'm a proud owner of the CTF2 shirt. This time I couldn't finish level4. My takeaway is: I invested too much time and shouldn't have done it. I guess I'll pass next time w…

I personally enjoyed learning more about the different languages that were used at each level. Granted I'd be meaning to try out node/scala/go in a more meaningful manner and the ctf problems were the perfect setting. The downside to this is that it can be difficult to learn a new language and solve the problem at hand.

I agree level4 was a bit undercooked and not as didactic as it could be. One could simply clear the level by using raft as a black box. Personally I enjoyed level 3 the most given the trade-offs that were present in solving it.

Re: Stripe-CTF 3 Writeup

#72

Post by danielweber » Fri, Jan 31, 2014, 4:04 PM UTC

jeremymcanally wrote: post #2

I got stuck on Level 3, partially because Scala is a little wacky (but I learned to appreciate it!) and partially because their specs were super terrible. They didn't mention it required substring matching or was case-sensitive until I'd been working on it for 2-3 days and then was out of time. Given the bad debug output (the head of a diff which often didn't show anything and didn't include what term the failure was…

> the head of a diff which often didn't show anything

They really needed "here are very small test cases to just find out if you doing things correctly." I spent at least a day wondering why things remotely were working locally but not working remotely when it turned out I wasn't giving file names in the proper format, something their "head of diff" format provided no feedback on.

Re: Stripe-CTF 3 Writeup

#73

Post by Strom » Fri, Jan 31, 2014, 5:09 PM UTC

henrikm85 wrote: post #68

Strom wrote: post #58

Earlier quoted context omitted.

Level1 was immensely satisfying and interesting, but the pvp challenge was .. well.. dead. By the time real life let me join others were throwing GPU based miners at the problem and traffic was constantly heavy anyway. So amazing level, the arena type thing was imho not a good idea. PvP challange dead .. but heavy traffic? Sounds like a contradiction. I think it's a flawed deduction that the arena was a bad idea beca…

Good job. Did you have previous experience with writing GPU code?

Had zero experience with programming for the GPU, or with OpenCL. Took this as an opportunity to learn both. I was surprised both with how amazingly fast the GPU is, and how amazingly buggy the AMD OpenCL compiler optimizer is. (Found multiple bugs where it generates memory corrupting code.)

Re: Stripe-CTF 3 Writeup

#74

Post by robbles » Sat, Feb 01, 2014, 1:49 AM UTC

gdb wrote: post #27

robbles wrote: post #25

Earlier quoted context omitted.

Same situation here. I'd love to work through the problems at my own pace over the next few weeks though - I'd also like a way of replicating the solution testing that Stripe performs when you do an actual submission. Is that infrastructure going to be released as well? Or would I need to just rely on the test harnesses and comparing my solution against the published ones?

You'll be stuck with the test harness for the foreseeable future, unfortunately. Releasing the submission infrastructure in a usable form would unfortunately be a looot of work. We're working on open-sourcing a lot of the dependencies, though.

Ok, that's probably enough for my learning purposes. Thanks!

Not having looked through all the problems yet - do they all have a reasonable test harness that gives you some sort of score?