0x0G CTF: gRoulette (Author Writeup)

0x0G is Google’s annual “Hacker Summer Camp” event. Normally this would be in Las Vegas during the week of DEF CON and Black Hat, but well, pandemic rules apply. I’m one of the organizers for the CTF we run during the event, and I thought I’d write up solutions to some of my challenges here.

gRoulette is a simplified Roulette game online. Win enough and you’ll get the flag. The source code is provided, and the entire thing is run over a WebSocket connection to the server.

gRoulette


0x0G CTF: Authme (Author Writeup)

0x0G is Google’s annual “Hacker Summer Camp” event. Normally this would be in Las Vegas during the week of DEF CON and Black Hat, but well, pandemic rules apply. I’m one of the organizers for the CTF we run during the event, and I thought I’d write up solutions to some of my challenges here.

The first such challenge is authme, a web/crypto challenge. The description just wants to know if you can auth as admin and directs you to a website. On the website, we find a link to the source code, to an RSA public key, and a login form.


GPU Accelerated Password Cracking in the Cloud: Speed and Cost-Effectiveness

Note: Though this testing was done on Google Cloud and I work at Google, this work and blog post represent my personal work and do not represent the views of my employer.

As a red teamer and security researcher, I occasionally find the need to crack some hashed passwords. It used to be that John the Ripper was the go-to tool for the job. With the advent of GPGPU technologies like CUDA and OpenCL, hashcat quickly eclipsed John for pure speed. Unfortunately, graphics cards are a bit hard to come by in 2021. I decided to take a look at the options for running hashcat on Google Cloud.


Making: A Desk Clamp for Light Panels

On a little bit of a tangent from my typical security posting, I thought I’d include some of my “making” efforts.

Due to the working from home for an extended period of time, I wanted to improve my video-conferencing setup somewhat. I have my back to windows, so the lighting is pretty bad, so I wanted to get some lights. I didn’t want to spend big money, so I got this set of Neewer USB-powered lights. It came with tripod bases, monopod-style stands, and ball heads to mount the lights.


BSidesSF 2021 CTF: Net Matroyshka (Author Writeup)

Net Matroyshka was one of our “1337” tagged challenges for the 2021 BSidesSF CTF. This indicated it was particularly hard, and our players can probably confirm that.

If you haven’t played our CTF in the past, you might not be familiar with the Matryoshka name. (Yep, I misspelled Matryoshka this year and didn’t catch it before we launched.) It refers to the nesting Matryoshka dolls, and we’ve been doing a series of challenges where they contain layers to be solved, often by different encodings, formats, etc. This year, it was layers of PCAPs for some network forensics challenges.