COMPFEST CTF 2023 - classroom

Description

Category: Misc

New semester has begun, this is a class room list for each day : https://bit.ly/Spreadsheet-Chall Wait.. why there is a flag page?

Flag : COMPFEST15{flag}

Author: kilometer

Resolution

There is a suspicious base64 encoded string in the spreadsheet:

SSBoaWQgdGhlIGZsYWcgb24gVHVlc2RheSdzIHNjaGVkdWxlIGJlY2F1c2UgSSBkaWRuJ3QgdGhpbmsgYW55IG9mIHRoZSBzdHVkZW50cyB3ZXJlIHRoYXQgc21hcnQh

Once decoded we get this:

I hid the flag on Tuesday's schedule because I didn't think any of the students were that smart!

Following the line with Tuesday, we notice that the cells looks like coordinates:

On the flag page, we have a table where we can decode each coodinate to a character:

We decode each coordinate with the table and we get the flag: COMPFEST15{V3rY_34Sy}.