Upon connecting to the server, a private ECDSA key is generated. You have 72 signature oracle calls and then you have to provide a forged signature. Twist is that you get to XOR whatever you want with the private key before signature is applied - which allows us to derive the private key one byte at a time.

See writeup for details.

Original writeup (https://4cad.github.io/CTF_Writeups/202007%20InCTF/Bakflipandsons/InCTF20%20-%20BakflipAndSons%20Writeup.html).