baseball

The Challenge

https://dreamhack.io/wargame/challenges/105

Do you watch baseball?

This challenge was pretty simple thanks to the power of AI.

Analyzing the binary

We are given a linux executable that takes a table and an input, and performs some type of mutation on the input.

We’re also given some sample text and the output of transforming that text. Ignore the IDA files…

The mutation algorithm looks really similar to the base64 algorithm. I asked DeepSeek what was going on here, and it confirmed my suspicions by telling me that this was base64 but with a different table!

This seems reminiscent to base64 encoding…

Base64 encoding uses this charset: ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/

All we need to do is to find out the charset being used to generate the encoded flag. Thankfully, we have the needed prerequisites:

1. Sample input and output
2. LLMs

With the help of Copilot, I was able to retrieve the table used for encoding the flag, and decrypt the flag.

I love AI