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Miss My School

  • Challenge: Miss My School
  • Category: OSINT
  • Flag: LYKNCTF{long_bien_elementary}

My initial read / first impressions

The challenge description says:

Talking about home makes me remember my old elementary school.

Using either point B or point C from the previous challenge (miss my home) as the starting point, my elementary school is located within a 2 km radius of one of those two points.

I am 18 years old now, and I started first grade in 2013. Find the elementary school I used to attend.

So this was basically a follow-up OSINT challenge. The previous challenge gave possible home-area points, and now this one says the elementary school is within 2 km of either point B or point C.

The attached image is clearly the front gate of a Vietnamese elementary school. The goal was not just to find any school nearby, but to identify the exact school from the visible details in the photo.

Looking at the image

The first obvious clues were the banners:

Ngày bầu cử đại biểu Quốc hội khóa XV
nhiệm kỳ 2021 - 2026

80 năm ngày thành lập Đội TNTP Hồ Chí Minh
15/5/1941 - 15/5/2021

These helped date the photo around 2021, but they did not identify the school directly. A lot of schools would have had the same political / anniversary banners.

The better clue was in the top right corner of the image. On the dark sign above the gate, there is a phone number:

ĐT: (04) 38 750 348

That was the real lead. Instead of trying to manually compare every school courtyard within the radius, I searched the phone number.

Searching the phone number

The old Hanoi area code was written as (04), so the number can also appear in modern listings as:

024 3875 0348

Useful searches were things like:

"38 750 348" school Hanoi
"024 3875 0348" "tiểu học"
"(04) 38 750 348"

Those searches pointed to:

Trường Tiểu học Long Biên

This also matched the image visually. The online listings / school pages show the same kind of entrance area, and the school name fits the Long Biên area from the previous challenge's points.

Verifying the school name

The important thing here is that the flag asks for the English-style normalized school name:

LYKNCTF{school_name_elementary}

The Vietnamese school name is:

Trường Tiểu học Long Biên

Removing the generic Trường Tiểu học part and converting the actual school name gives:

Long Biên -> long_bien

Then adding _elementary gives:

long_bien_elementary

Why this works

The 2 km radius clue narrows the map down, but the image itself gives the unique identifier. The banners are mostly noise because many schools had the same 2021 election / youth organization decorations.

The phone number is the clean pivot:

(04) 38 750 348
    -> 024 3875 0348
    -> Trường Tiểu học Long Biên
    -> long_bien_elementary

So the solve is mostly about not overcomplicating the map search. Once I noticed the phone number, the school became unambiguous.

Final flag

LYKNCTF{long_bien_elementary}