Alexander Koch

Quantum cryptography allows to achieve security goals that are unobtainable using classical cryptography alone, it offers the promise of everlasting privacy. That is, an adversary trying to attack a protocol must succeed during the run of the protocol, after the protocol has terminated security holds unconditionally. In this work we initiate the study of a new model which we call the quantum decoherence model (QDM). In a nutshell, this model requires that the adversary is computationally bounded during the run of a protocol (and some time after), but becomes computationally unbounded long after the protocol terminates. Importantly, once the adversary becomes computationally unbounded, he can only remember a bounded number of qubits from before the bound was lifted. As our main contribution, we construct a non-interactive commitment scheme achieving unconditional security against malicious senders and everlasting security against malicious receivers in the UC model. Additionally, we show that it gives rise to everlasting public key encryption and OT in the QDM. Finally, we also consider the weaker notion of incompressible encryption in the setting of quantum decoherence, and show that post-quantum IND-CPA secure public key encryption is sufficient to realize this notion without resorting to random oracles.