Applied Cryptography expert

BlackAlps 2019 - Schnorr

Schnorr signature with a Blum-Blum-Schub PRNG to generate the nonce. Since the quadratic equation can be solved in the prime group the private key can be recover from two consecutive signatures.

GreHack 2019 - Delayed Memories - The Grid

Reverse challenge which is finally a maze. A move is encoded on 2 bit of a character given as input. The combination which gets you out of the maze is the flag. We present here three different ways to solve the challenge.

N1CTF 2019 - Part3-BabyRSA

RSA encrypted flag but each flag bit is encrypted at a time with random padding. The padding is a square thus using computing the Jacobi symbol for each bit encryption reveals the flag.

Insomni'hack 2019 - INSFS

A serial connection gives access to a basic filesystem. Repairing the filesystem with debug tools and adjusting an offset gives access to protected data.