HKCERT CTF 2021 Postmortem (IV): The Remaining Ones

HKCERT CTF 2021 Postmortem (IV): The Remaining Ones
We will cover the remaining challenges I wrote in this part: Flag Checker™, The Wilderness and Potion of Ciphermath.
Read more →

HKCERT CTF 2021 Postmortem (III): The Reverse Challenges

HKCERT CTF 2021 Postmortem (III): The Reverse Challenges
As the third part of the series, three reversing challenges will be included: The Hardest Path, A Junior Mathematician and Let’s Chill.
Read more →

HKCERT CTF 2021 Postmortem (II): Harder Crypto Challenges

HKCERT CTF 2021 Postmortem (II): Harder Crypto Challenges
In this part, three harder crypto challenges will be covered: Tenet: The Plagarism, Sratslla SEA and Sign in Please, Again.
Read more →

HKCERT CTF 2021 Postmortem (I): Easier Crypto Challenges

HKCERT CTF 2021 Postmortem (I): Easier Crypto Challenges

Black Bauhinia coorganized HKCERT CTF 2021 and helped 95% of the technical stuffs, including challenge setting, platform development, infrastructure and etc. I will be writing a series of blog posts talking about the contest, and the first four would be the writeups of the challenges those I wrote.

In the first blog post, we will be going through four easier crypto challenges: A Joke Cipher, Cipher Mode Picker, Key Backup Service 1 and Key Backup Service 2.

Read more →

HKCERT CTF 2020 Postmortem

HKCERT CTF 2020 Postmortem
On August 2020, @blackb6a was invited to co-organize HKCERT CTF 2020 (which is held on November 2020) as one of the challenge authors. This is a CTF for secondary and tertiary students in Hong Kong. Although I had experience preparing CTFs earlier, this is actually the first CTF officially prepared by Black Bauhinia. I have written four challenges for this CTF - Sanity Check II (Web), LF2 (Reverse), Sign In Please (Crypto) and Calm Down (Crypto). There will also be some stories behind the scenes.
Read more →

hoifanrd’s osu! Challenge

hoifanrd's osu! Challenge
This is a beginning of a new series of blog posts that I review CTF challenges those are not publicly accessible. Generally I will spend some time to solve the challenge while discussing with the author, and give some feedback of the challenge. To kick-start, let’s look at hoifanrd from Firebird CTF team has shared a challenge he created some days ago.
Read more →

Firebird Internal CTF Writeup

I have written four question for Firebird Internal CTF - Oofbleck (Crypto), Obvious Transfer (Crypto), RC4 (Misc) and Prooof-ooof-Wooork (Reverse, Misc). I will be including all of them in this blog post.
Read more →

Firebird Intro CTF: Rotten Secured Algorithm

Rotten Secured Algorithm is the only challenge that I have written for Firebird Intro CTF. Two people (out of 166) ended up solving the challenge. There is a Python script attached in the challenge, as well as the output file. Let’s see what’s going on in the Python…
Read more →