Quantum digital signatures (QDS) provide a means for signing electronic
communications with informationtheoretic security. However, all previous
demonstrations of quantum digital signatures assume trusted measurement
devices. This renders them vulnerable against detector side-channel attacks,
just like quantum key distribution. Here, we exploit a
measurement-device-independent (MDI) quantum network, over a
200-square-kilometer metropolitan area, to perform a field test of a
three-party measurement-device-independent quantum digital signature (MDI-QDS)
scheme that is secure against any detector side-channel attack. In so doing, we
are able to successfully sign a binary message with a security level of about
1E-7. Remarkably, our work demonstrates the feasibility of MDI-QDS for
practical applications.Comment: 5 pages, 1 figure, 2 tables, supplemental materials included as
ancillary fil
