HKCERT CTF 2023 Postmortem (III): The Remaining Challenges
![HKCERT CTF 2023 Postmortem (III): The Remaining Challenges](https://mystiz.hk/images/2024-01-27-hkcert-ctf/cover-3.jpg)
HKCERT CTF 2023 Postmortem (II): Harder Crypto Challenges
![HKCERT CTF 2023 Postmortem (II): Harder Crypto Challenges](https://mystiz.hk/images/2024-01-27-hkcert-ctf/cover-2.jpg)
HKCERT CTF 2023 Postmortem (I): Easier Crypto Challenges
![HKCERT CTF 2023 Postmortem (I): Easier Crypto Challenges](https://mystiz.hk/images/2024-01-27-hkcert-ctf/cover-1.jpg)
HKCERT CTF 2022 Postmortem (III): The Remaining Challenges
![HKCERT CTF 2022 Postmortem (III): The Remaining Challenges](https://mystiz.hk/images/2022-12-24-hkcert-ctf/minecraft-geoguessr.png)
HKCERT CTF 2022 Postmortem (II): Harder Crypto Challenges
![HKCERT CTF 2022 Postmortem (II): Harder Crypto Challenges](https://mystiz.hk/images/2022-12-24-hkcert-ctf/mystiz-cant-code.png)
HKCERT CTF 2022 Postmortem (I): Easier Crypto Challenges
![HKCERT CTF 2022 Postmortem (I): Easier Crypto Challenges](https://mystiz.hk/images/2022-12-24-hkcert-ctf/catch-22-summary.png)
This is the third year Black Bauhinia co-organized HKCERT CTF. This time I wrote nine challenges: Seven crypto, one reverse and one misc.
Similar to the last year, I have a series of three blog posts walking through the challenges that I wrote. We will discuss the four easier crypto challenges: Flawed ElGamal, Catch-22, Rogue Secret Assistant and Base64 encryption.
HKCERT CTF 2021 Postmortem (IV): The Remaining Ones
![HKCERT CTF 2021 Postmortem (IV): The Remaining Ones](https://mystiz.hk/images/2021-11-18-hkcert-ctf/thumbnail-4.png)
HKCERT CTF 2021 Postmortem (III): The Reverse Challenges
![HKCERT CTF 2021 Postmortem (III): The Reverse Challenges](https://mystiz.hk/images/2021-11-18-hkcert-ctf/thumbnail-3.png)
HKCERT CTF 2021 Postmortem (II): Harder Crypto Challenges
![HKCERT CTF 2021 Postmortem (II): Harder Crypto Challenges](https://mystiz.hk/images/2021-11-18-hkcert-ctf/thumbnail-2.png)
HKCERT CTF 2021 Postmortem (I): Easier Crypto Challenges
![HKCERT CTF 2021 Postmortem (I): Easier Crypto Challenges](https://mystiz.hk/images/2021-11-18-hkcert-ctf/thumbnail-1.png)
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.
HKCERT CTF 2020 Postmortem
![HKCERT CTF 2020 Postmortem](https://mystiz.hk/images/2021-03-28-hkcert-ctf/sanity-check.png)