Rating:

* The key point was to recover the IV which was used in AES .
* It can be easily noted that pad function adds 16 bytes of hex("16") at the end of the plaintext.
* As EBC is used ,the 2 plaintext blocks will be encrypted to same ciphertext and therefore the returned hex string[-16:] is the IV.
* Now you have everything you need and you can decrypt the ciphertext blocks one by one :)

Original writeup (https://github.com/0m3g4-ops/DU_CTF/blob/master/extra_cool_blockchain.py).