CrossCTF_2017: Paricle Collision Challenge

Category: Cryptography Points: 5 Description:

Our large hadron collider feeds off files that produces the same SHA1 hashsum value. Could you help us power up our collider? We will give you a flag in return! Our collider can be found at http://128.199.98.78:8081/

Hint:

The collider feeds on distinct pairs of files that produces the same SHA1 hashsum value. However, the collider only accepts files it hasn't seen before!

Write-up

This is a simple one, given that SHA1 is entirely broken and collisions are easily generated. For the purpose of this challenge, we will use a SHA1 collider, yielding two PDFs that result in the same hash.

Therefore, the flag is CrossCTF{[email protected]_C0llid3d!}.