Time passes quickly, and we reach the end of 2025. This year is a memorable year with me because lots of things happened, so I want to save good memories here.

This post is inspired from Mystiz’s retrospective series, so don’t surprise if you feel the style is similar.

Capture-The-Flag

I think I’m really active in CTF in 2025. This year, I played with many CTF teams with different roles, from member, intern to guest. I’m really happy to meet and play with many strong and cool players. Its a valuable experience to see how insanely good players approach the problem and solve that.

I played with @idekCTF, @r3kapig, @Infobahn_ctf, @malta_ctf when I want to try hard with hard CTF competition; played with @uit_inseclab, which is my university CTF team for university competition; and with @1337Yogurt when I want to travel (already did it!) and have fun with my friend. Sometimes I played solo with name yaua xD.

As a CTF player, my favorite challenges this year are These Walls in Codegate CTF 2025 Preliminary as I found the concept is amazing; and service Crypto01 in CSCV because it’s the first time I tried a crypto service in Attack-Defense. Hope one day I can make good challenges like that. I also notice that I had lots of second blood this year, for either play with team or solo.

As an author of CTF competitions, I wrote 10 challenges for idekCTF 2025 (I also wrote a detail writeup at here) and WannaGame Championship 2025. My favorite challenges are Sadness ECC because I took the idea from a problem in a Vietnam mathematical contest and found it’s really cool; Interesting Signing because it’s the first time I wrote a challenge in C and luckily there’s no unintended pwn bug.

CTF competitions was really fun in first half of this year, but from second half, LLMs became smarter and can solve lots of Cryptography challenges. I attended lots of competitions that crypto category is full cleared in ~1 hours, it makes me really sad and feel like CTF is not fun anymore…

Trip

I had two big trips in this year! Its the main reason to make my 2025 so perfect.

Korea

The first one is the trip to Korea for Hacktheon Sejong Final with @1337%Yogurt, and I was really excited because it’s the first time I gone to another country and attended in final competition. Although the visa step took nearly one months, its worth for good memories I had. The competition was held really nice with excellent preparation, and I was destroyed with great set of challenges.

After competition, because I don’t know any place in Sejong except place that my team competed, my friends suggest going to Seoul and turn out its good option. I went to Myeongdong night market and shocked with density of visitors here, and the food is really good. I also visited LoL Park and Korea University and had a lunch with @is0m0rph1sm and @ksprsk, which is the best moment I had in that trip.

Hanoi

The second one is the trip to Hanoi to attend Young Cryptographer Forum and AsiaCCS'25. This is a great oppotunity for me to see what a real world cryptographer does, besides learning cryptography via CTF. With lots of new topic from many lecturers, my small brain was exploded, but also really impressive with their works, and wish one day I could be as good as them. At these events i was sticked with BKISC and Blackpinker - which are other university’s CTF teams in HCMC. We discussed about all topics in both events and travelled together, and I was very appreciatived for what they did with me.

Because the events is really near with Vietnam National Day, so I decided to stay at Hanoi 1-2 day more to travel. The streets and tourist attractions is decorated beautifully with flags and lamps, and I could see lots of national visitors everywhere. I could feel the bustling atmosphere of the city at that time. I also have a fun time with my friends who are live in Hanoi, one of them spent many time to make a really detailed plan for me to visit many well-known places, so my phone is full of pictures haha. I’m really lucky to know and meet them.

Life

I nearly finish my bachelor program, and only need to defend my thesis in January next year. The last two semesters made me really tired as there are lots of exams and projects, but somehow I still can pass it. Thank @kyr04i for helped me a lots in these subjects (and in CTF too).

For work place, I was approached with many cool concepts in this year, mostly about cryptographic protocols and how big cryptocurrency companies use it in their products. Really fun that I can apply my knowledge from CTF to approach with these protocols, and I can also solve some challenges with the knowledge I got when learning these schemes (Crypto01 is an example), feel like its a win-win relationship.

At some points, I was really depressed because lots of things happened with me in life, but travelling and talking with friends I got in both trip helps my mental health very much. I also should change my unhealthy lifestyle in next year.

Next year’s plan

• Healthier lifestyle and spend more time for relationships. I should touch grass and go outside more, as I feel my physical health is bad in this year.
• Focus on one topic. I feel like I don’t have deep knowledge for everything I know right now, so I don’t have good enough output. I should lock in at only one target.
• Play CTF in a different way. I still love playing CTF, but LLMs are too strong these days, and it makes CTF competitions became boring. Maybe I should try my best to make a challenge which is not LLM-able, and I think its worth to do it.
• Travel more. I found its a very good way to reduce stress and recharge my battery, so I will work harder to find a chance to travel and meet new friends.
• Write more post.

Thanks for reading my recap for 2025, and wishing you all the magic of the new year.