The postprocessing of quantum digital signatures

Denis Butin, Stefan-Lukas Gazdag, Johannes A Buchmann

Bing-Hong Li, Yuan-Mei Xie, Xiaoyu Cao +4 more

Quantum digital signatures (QDSs), generating correlated bit strings among three remote parties for signatures through quantum law, can guarantee nonrepudiation, authenticity, and integrity of messages. Recently, a one-time universal-hashing QDS framework, exploiting the quantum asymmetric encryption and universal hash functions, has been proposed to significantly improve the signature rate and ensure unconditional security by directly signing the hash value of long messages. However, similar to quantum key distribution, this framework utilizes keys with perfect secrecy by performing privacy amplification that introduces cumbersome matrix operations, thereby consuming large computational resources, causing delays, and increasing failure probability. Here, we prove that, different from private communication, imperfect quantum keys with partial information leakage can be used for digital signatures and authentication without compromising the security while having eight orders of magnitude improvement on signature rate for signing a megabit message compared with conventional single-bit schemes. This study significantly reduces the delay for data postprocessing and is compatible with any quantum key generation protocols. In our simulation, taking two-photon twin-field key generation protocol as an example, QDS can be practically implemented over a fiber distance of 650 km between the signer and receiver. For the first time, this study offers a cryptographic application of quantum keys with imperfect secrecy and paves a way for the practical and agile implementation of digital signatures in a future quantum network.

Kwangjo Kim

Vedran Dunjko, Petros Wallden, Erika Andersson

Quantum digital signatures (QDSs) allow the sending of messages from one sender to multiple recipients, with the guarantee that messages cannot be forged or tampered with. Additionally, messages cannot be repudiated--if one recipient accepts a message, she is guaranteed that others will accept the same message as well. While messaging with these types of security guarantees are routinely performed in the modern digital world, current technologies only offer security under computational assumptions. QDSs, on the other hand, offer security guaranteed by quantum mechanics. All thus far proposed variants of QDSs require long-term, high quality quantum memory, making them unfeasible in the foreseeable future. Here, we present a QDS scheme where no quantum memory is required, which also needs just linear optics. This makes QDSs feasible with current technology.

Petros Wallden, Vedran Dunjko, Adrian Kent +1 more

Digital signatures guarantee the authenticity and transferability of messages and are widely used in modern communication. The security of currently used classical digital signature schemes, however, relies on computational assumptions. In contrast, quantum digital signature (QDS) schemes offer information-theoretic security guaranteed by the laws of quantum mechanics. We present two QDS protocols which have the same experimental requirements as quantum key distribution, which is already commercially available. We also give a security proof for the presented QDS schemes against coherent forging attacks.

Qirui Luo