Fault-tolerant quantum data locking

Quantum data locking is a quantum communication primitive that allows the use of a short secret key to encrypt a much longer message. It guarantees information-theoretical security against an adversary with limited quantum memory. Here we present a quantum data locking protocol that employs pseudorandom circuits consisting of Clifford gates only, which are much easier to implement fault tolerantly than universal gates. We show that information can be encrypted into n-qubit code words using order n − Hmin (X) secret bits, where Hmin (X) is the min-entropy of the plain text, and a min-entropy smaller than n accounts for information leakage to the adversary. As an application, we discuss an efficient method for encrypting the output of a quantum computer.