Superposition attacks and fully-quantum cryptography

In a typical post-quantum scenario, the adversary has a quantum computer at their disposal, but only gets classical access to the cryptographic scheme. Recent research has shown that, if adversaries also get quantum access (e.g., the ability to encrypt or authenticate in superposition) then they can easily break many constructions currently believed to be “quantum-secure.”

In this talk, we will discuss these “quantum CPA attacks” in two settings. First, in the setting of quantum attacks against classical cryptography, we will talk about which schemes remain secure and which ones are broken (and how to fix the broken ones.) We will also mention some difficulties in giving sensible definitions of quantum-secure classical authentication. Second, in the setting of quantum attacks against quantum cryptography, we will show how to use classical primitives to build encryption schemes for quantum data. Time-permitting, we will also touch upon more advanced constructions (such as fully-homomorphic encryption and obfuscation) in this setting.