In addition to using end-to-end encryption, Signal also uses perfect forward secrecy (PFS). What is PFS? It’s a system that uses a slightly different encryption key for every call, so that even if someone does manage to get hold of your encrypted phone call and the key that was used to encrypt it, your other calls will remain secure. All PFS keys are based on a single original key, but the important thing is that if someone compromises one key, it doesn’t mean your potential adversary has access to your further communications.
