SpookyCTF'23: If the Key Fits…

I am trying to escape this 64-story horror house and the only way to escape is by finding the flag in this text file! Can you help me crack into the file and get the flag? The only hint I get is this random phrase: MWwwdjM1eW1tM3RyMWNrM3Q1ISEh

This was a simple AES decrypting challenge. We are given a flag.txt.aes file along with the random phrase.

The analysis

As per the file extension, the flag.txt.aes file is encrypted using AES. Tools like AESCrypt, OpenSSL, etc. can be used to decrypt the file. However, we need the key to decrypt the file.

Getting the Key

Plugging the random phrase into a Cipher Identifier online tool, it flagged it out as Redefence Cipher or Base64 Coding.

I tried both tools, and Base64 decoding gave me the key:


Decrypting the File

Now that we have the key, we can go on with decrypting the AES file. I used AESCrypt’s CLI tool:

kairos@pop-os:~/Downloads$ aescrypt -d  flag.txt.aes
Enter password:

Entering 1l0v35ymm3tr1ck3t5!!! in the prompt unlocked the file :D

Looking at flag.txt:


We got the flag :)