The Underhanded C Contest

> The contest was initially inspired by Daniel Horn’s Obfuscated V contest in the fall of 2004 (note: the original page is long gone, and this link goes to a snapshot from archive.org). The object of that contest was to write a simple program to count votes, that somehow miscounts the votes on election day. I was greatly impressed to see how even a short program to simply count characters in a text file can be made to fail, and fail only on one specific day, so that the bug isn't noticed in testing.

https://underhanded-c.org/_page_id_7.html

Re: The Underhanded C Contest

#6

Post by theteapot » Thu, Jul 02, 2026, 12:56 AM UTC

TZubiri wrote: post #4

AmazingEveryDay wrote: post #2

(2015). RIP.

2026 calls for an Underhanded prompt contest

Or better, sleeper agents. Anthropic released a study on this in 2024 "Sleeper Agents: Training Deceptive LLMs that Persist Through Safety Training" -- https://www.anthropic.com/research/sleeper-agents-training-d..., https://www.youtube.com/watch?v=_y9j2BoHg2c

Re: The Underhanded C Contest

#7

Post by silisili » Thu, Jul 02, 2026, 1:19 AM UTC

BiraIgnacio wrote: post #5

> The contest was initially inspired by Daniel Horn’s Obfuscated V contest in the fall of 2004 (note: the original page is long gone, and this link goes to a snapshot from archive.org). The object of that contest was to write a simple program to count votes, that somehow miscounts the votes on election day. I was greatly impressed to see how even a short program to simply count characters in a text file can be made t…

The original page actually loads fine, maybe was restored later?

I looked through a few trying not to read the short description and missed a lot of simple things, really makes you think...

https://graphics.stanford.edu/~danielh/vote/vote.html

Re: The Underhanded C Contest

#8

Post by pseudohadamard » Thu, Jul 02, 2026, 3:21 AM UTC

Interesting that the case they were using was the Nuclear Threat Initiative and FP uncertainties, I've audited some, ah, nuclear-physics-related code that had an issue due to FP uncertainties...

Re: The Underhanded C Contest

#9

Post by ForOldHack » Thu, Jul 02, 2026, 5:40 AM UTC

gwern wrote: post #3

AmazingEveryDay wrote: post #2

(2015). RIP.

At least we still have https://www.ioccc.org/2025/index.html#inventory !

Oh my god, and to think that OCC used to just be ways to torture the pre-processor... stunning work. Utter and complete no holds barred mud.

Re: The Underhanded C Contest

#10

Post by ForOldHack » Thu, Jul 02, 2026, 5:41 AM UTC

pseudohadamard wrote: post #8

Interesting that the case they were using was the Nuclear Threat Initiative and FP uncertainties, I've audited some, ah, nuclear-physics-related code that had an issue due to FP uncertainties...

Where you can encode an entire Command and Control server within rounding errors! You sneaky skunk!