An uncloneable encryption scheme encodes a classical message as a quantum ciphertext in order to guarantee that two non-interacting adversaries cannot both learn the message, even when given the encryption key. This defines a stronger classically-impossible notion of security, as any classical ciphertext can be copied. So far, a security proof for uncloneable encryption has been elusive. We show that uncloneable encryption exists with no computational assumptions, with security inverse-polynomial in the security parameter. We use properties of a monogamy-of-entanglement game associated with the Haar-measure encryption to guarantee that any state that succeeds with high probability cannot be close to maximally-entangled between the referee and either of the players, whence we can apply a decoupling theorem to show that either player becomes completely uncorrelated, and therefore cannot win significantly better than random guessing.

This is joint work with Eric Culf, based on https://arxiv.org/abs/2503.19125. AB via the Perimeter Institute is supported in part by the Government of Canada through the Department of Innovation, Science, and Economic Development Canada and by the Province of Ontario through the Ministry of Colleges and Universities.