CTF writeups
TapeThe description of this challenge is: “We’ve found this priceless, old magnetic tape in our archives. We dumped the contents, but the data is corrupted and we can’t read it. We only have this old tape reader tool, but source code was lost long ago. The program has only 944 bytes, so reversing it should… Continue reading Google CTF 2018 – Tape
The legacy ZIP crypto is long broken, so we’ve fixed it In this challenge, we are provided with a Python script (better_zip.py) that generates an encrypted zip file from an input file and key, and want to decrypt flag.zip, which was generated with this script. The script has two main parts: a BetterZipCreator class that… Continue reading Google CTF 2018 – Better Zip
We are given a pcap file, so let’s open it up in Wireshark: As can be seen, the entire pcap consists of USB packets. The overall structure of the file is something like: At the beginning, the host asks a USB device for its descriptors (i.e. configuration information). Then, the host repeatedly sends SET_REPORT requests… Continue reading Google CTF 2018 – Feel It
This challenge was a follow-up to an earlier challenge, titled "Palindromes Pairs - Coding Phase". In that earlier warmup ppc challenge, the goal was to write an algorithm to solve the following problem: given up to 1000 strings $latex s_i$, each of length at most 1000, count the number of pairs $latex (i, j)$ such… Continue reading Tokyo Westerns CTF 2017 – Palindromes Pairs (Challenge Phase)
On the surface, this challenge appears to be about secret sharing. The setup is simple: the flag is divided into $latex N=100$ pieces using Shamir's secret sharing scheme so that it can be recovered given any $latex K=25$ of these pieces (but is impossible to recover with any fewer). The server provides you with all… Continue reading Tokyo Westerns CTF 2017 – Liar’s Trap
The goal of this challenge is to successfully run (in a shell on a provided server) a setuid binary flag which asks you to repeat a number, and then (if you repeat it successfully) outputs the flag: This would be trivial but for one interesting restriction of the provided shell: the only characters you are… Continue reading 33C3 CTF – shjail
In this challenge, we are provided with a 32-bit ELF ('babyfengshui') and a libc file ('libc-2.19.so'). The program maintains a list of users, which consist of names and descriptions. Here is some example usage, where we add a user and then display it: As you can see, there are 4 relevant actions, so let's go… Continue reading 33C3 CTF – babyfengshui
