Erika Andersson, Institute of Photonics and Quantum Sciences Heriot-Watt University
Digital signatures ensure that messages cannot be forged or tampered with. They are widely used to provide security for electronic communications, for example in financial transactions and electronic mail. Importantly, signed messages are also transferrable, meaning that if one recipient accepts a message as genuine, then she is guaranteed that others will also accept the same message if it is forwarded. Digital signatures are different from encryption, which guarantees the privacy of a message. Currently used classical digital signature schemes, however, only offer security relying on unproven computational assumptions. In contrast, quantum digital signatures, similar to quantum key distribution, offer information-theoretic security based on principles of quantum mechanics. A serious drawback of previous quantum digital signature schemes is however that they require long-term quantum memory, making them unfeasible. We present protocols which do not need quantum memory and which use only standard linear optical components and photodetectors. With this, it seems that quantum digital signatures and quantum key distribution are similar in terms of experimental requirements. Important work remains: to investigate which quantum digital signatures schemes are most suited for real applications, to complete full security proofs, and to establish the relation, in terms of functionality and efficiency, between quantum digital signatures and different types of classical signature schemes.