---
# System prepended metadata

title: HCMUS CTF 2023

---

# HCMUS CTF 2023

## Misc

### japanese

có lyrics:
![](https://hackmd.io/_uploads/SycwMVBNn.png)

Search google:
![](https://hackmd.io/_uploads/S1AKMEBE3.png)

![](https://hackmd.io/_uploads/H1x6fVBE3.png)

flag:

```HCMUS-CTF{ifuudoudou-gumi_hatsunemiku_ia_kagaminerin_megurineluka}```

### grind

Thêm 3 file db vào DB Browser

![](https://hackmd.io/_uploads/rJcH74H42.png)

Đề có ghi rằng tài khoản tạo gần trước 2019, có một bài post trên reddit chỉ ra uid và thời gian tham gia game:

https://www.reddit.com/r/Granblue_en/comments/eyhg1m/help_with_making_a_gbf_id_timeline/

![](https://hackmd.io/_uploads/Sy5nQ4rN2.png)

=> uid khoảng 23k->25k5

points day 3 khoảng 900M

=> points day3 - points day2 ~ 900M

query:
```sql
select * from "data-64-final".ranking as df where df.uid in
(select uid from "data-64-final".ranking where(rank >5000)
INTERSECT
select d3.uid from "data-64-day3".ranking as d3, ranking as d2 where d3.uid = d2.uid and (d3.points - d2.points between 900000000 and 1000000000))
and uid BETWEEN 23000000 and 25500000
order by rank ASC
```

query khoảng 30 user

có user tên ζ(2)

![](https://hackmd.io/_uploads/HyLq84S42.png)


liên quan đến hàm zeta riemann

![](https://hackmd.io/_uploads/H1O9SVrV2.png)

tính hàm đó ta được ![](https://hackmd.io/_uploads/Hyg2HNHN3.png)

```HCMUS-CTF{23983477-1.6449340668-2391789368-9614}```

## Forensics

Ta thấy dump lsass, dùng mimikatz để lấy credentials:

![](https://hackmd.io/_uploads/H1FMLNHNh.png)
