Crypto - Infinite Descent

So I am trying to solve this really interesting Crypto challenge, Infinite Descent. I (think) have decoded the given message using private key and I used the result to generate AES key (don’t know it’s correct or not). Now I am not sure what’s the next step, I tried submitting the key as flag but failed. Can anyone please give me a hint? Thanks.

take a look at the files provided to you again, especially the python scripts. Read them again (including the comments) and figure out the next step.

@trschober Thanks, did it for me, too.