GCM Nonce Reuse

In this exercise, we explore the critical vulnerability that arises from reusing the same nonce (IV) in Galois/Counter Mode (GCM) encryption. The lab provides a practical demonstration where users must register an account, post messages, and utilize XOR operations to retrieve the encryption key. By understanding the provided encryption code, which mistakenly uses a fixed IV, and leveraging XOR operations, participants can decode the encrypted messages and uncover the key.

The video transcript walks through the steps needed to exploit this weakness, from registering an account to posting messages and finally using a Ruby script to perform the necessary XOR operations. This exercise emphasizes the importance of proper nonce management in encryption algorithms and highlights the severe security implications of neglecting this aspect.