**Full write-up:** [https://www.sebven.com/ctf/2021/08/29/WORMCON0x012021-Fake-Encryption.html](https://www.sebven.com/ctf/2021/08/29/WORMCON0x012021-Fake-Encryption.html)

Cryptography – 379 pts (12 solves) – Chall author: BUILDYOURCTF

A PNG containing the flag is first encrypted with DES-ECB, then another copy is first shuffled in blocks of 8 bytes followed by the same encryption. We are given the encrypted flag PNG and both the raw and encrypted shuffled PNGs. Due to the nature of the ECB mode and the DES block size being 8 bytes, we are able to easily recover the original flag PNG.

Original writeup (https://www.sebven.com/ctf/2021/08/29/WORMCON0x012021-Fake-Encryption.html).