Day 06 - Unwrap The Gift
Description
Root-Me's Santa is being very generous this year, giving everyone who comes to see him a little present, but he's made sure you can't open it until the 25th…
Author : Mika nc 163.172.68.42 10006
all files in resources/ were provided.
Challenge
Looking at the code provided we see that the same IV is used to encode 2 different messages.
The first is our flag, which we don't know, the second is a custom user prompt.
Using this information we can easily get IV back.
Let's recap, we have.
C_known -> a known ciphertext
P_known -> a known plaintext
C_unknown -> the flag ciphertext
P_unknown -> the flag
From this we can do:
IV = C_known ^ P_known
P_known = C_known ^ IV
The only requirement is for the P_known to be long enough to be able to decode the whole flag.
Let's make our reverse.py and get the flag.