RSA-CBC

Round: 27 (2022/10)
Category: Crypto
Points: 75
Solves: 35

Description

I fixed the problem of the previous attempt in mixing RSA and block ciphers.

Solution

The iv of each block is always known, so you can bruteforce the characters by checking

$$ (\text{iv}+x)^e \stackrel{?}{\equiv} \text{ct} \pmod{n} $$