According to the no-cloning principle of quantum information, it is not possible, in general, to duplicate an unknown quantum state. In this talk, we will discuss how his unclonability property permeates quantum cryptography.
We start with the early finding of Wiesner on unforgeable quantum money, that established a technique called conjugate coding, which encoding information in random, nonorthogonal bases. This technique is, today, at the foundation of much of quantum cryptography and it plays a key role in the groundbreaking work of Bennett and Brassard on quantum key distribution.
We next discuss recent work that shows how conjugate coding enables certified deletion: a way to unconditionally certify that encrypted information has been erased, meaning that an adversary cannot read the original information, even if the entire decryption key is revealed. This feat is clearly impossible with classical encodings alone.
Finally, we will review unclonable encryption, which, once more, is a situation where we use conjugate coding and, via a monogamy-of-entanglement relation are able to show that the quantum encryption scheme allows to unconditionally prevent an adversary from duplicating the underlying plaintext, meaning that it is impossible for two malicious recipients to decrypt, even if the key is completely leaked.
