Capture The Flags / Write-Ups / osu!gaming CTF 2025 / circles

Both osu! and this game consist of circles... And the latest version of the game is also named CiRCLE...

Anyway, we found out an evil group is trying to encode some secret message in their usernames.

The only info we get is the image below, please help us!

P.S. The flag contains non-ascii characters, and you should wrap it in osu{FLAG} format.

P.P.S. You don't have to touch grass in order to solve this challenge :)

From the challenge description, we can find that the image is from Maimai.

• The bottom-right corner of the image has the text "IGAME(TAI PO)".
• Searching the text, we'll find 大埔桌球娛樂城 i-Game.
• This is a YouTube channel that livestreams Maimai gameplay from an arcade in Hong Kong.

Look for the livestream from 10/23, the date on the image.

• At around 19:54.56, we can find two cryptic usernames

• Put SfCfkpZN and NGnwn5iL into CyberChef.

• In Base64, SfCfkpZNNGnwn5iL decodes into "I💖M4i😋".

As the challenge description mentioned, the flag contains non-ascii characters.

Therefore, we obtained the flag for rhythm/circles.

Flag: osu{I💖M4i😋}