Mass-Surveillance Without The State: Strongly Undetectable Algorithm-Substitution Attacks

We present new algorithm-substitution attacks (ASAs) on symmetric encryption that improve over prior ones in two ways. First, while prior attacks only broke a sub-class of randomized schemes having a property called coin injectivity, our attacks break all randomized schemes. Second, while prior attacks are stateful, ours are stateless, achieving a notion of strong undetectability that we formalize. Together this shows that ASAs are an even more dangerous and powerful mass surveillance method than previously thought. Our work serves to increase awareness about what is possible with ASAs and to spur the search for deterrents and counter-measures.