Hangzhou was rainy again today, making it difficult to feel energetic. I swore long ago that I would stop procrastinating, but nothing has changed after several years. After both the DEF CON CTF 2020 Finals and the 2021 Qualifiers, I confidently planned to publish something, only to abandon it each time. I could not postpone it again, so here is an account of my two days in Shanghai.
The endless exams finally ended, and after half a year I returned to competing with my AAA teammates—and to staying up all night. We solved five of the six reverse-engineering challenges. The remaining one, RL_Env, appeared to involve machine learning; I did not even understand what it was asking us to do.
I realized that the blog had not been updated for a year, so it was time to fill in one of the gaps.
TCTF 2020 began at 10 a.m. and lasted 24 hours. My teammates and I spent the entire day competing in room 108, until I could no longer stay awake and fell asleep at 4 a.m. We ultimately placed second in the Rising Star division. In KoH, we lost to NeSE because we could not determine how to wire an S-box efficiently from logic gates.
The challenge provided a small USB circuit board. Once connected, it behaved like an emulated mouse and drew the flag one character at a time. Its drawing speed continually decreased, so it clearly could not finish before the competition ended.
First convert the supplied firmware to binary with a tool such as hex2bin. Open it in IDA, select Atmel AVR as the processor and ATmega32 (or another suitable model) as the device, and the firmware can be disassembled.
At least the wired network on Zijingang’s Yuquan campus has IPv6. While doing a computer networking assignment, I took the opportunity to investigate IPv6 network programming.