Abstract
Quantum key distribution (QKD) provides means for unconditional secure key transmission between two distant parties. However, in practical implementations, it suffers from quantum hacking due to device imperfections. Here we propose a hybrid measurement attack, with only linear optics, homodyne detection, and single photon detection, to the widely used vacuum + weak decoy state QKD system when the phase of source is partially randomized. Our analysis shows that, in some parameter regimes, the proposed attack would result in an entanglement breaking channel but still be able to trick the legitimate users to believe they have transmitted secure keys. That is, the eavesdropper is able to steal all the key information without discovered by the users. Thus, our proposal reveals that partial phase randomization is not sufficient to guarantee the security of phase-encoding QKD systems with weak coherent states.
Highlights
Quantum key distribution (QKD) provides means for unconditional secure key transmission between two distant parties
Y1L and eU1 are the lower bound of yield and upper bound of QBER for single photon pulses, which must be estimated by Alice and Bob according to their measurement results
In some parameter regimes, when Eve is present, the legitimate parties will be cheated and the estimated key rate is still positive, but the generated key are insecure, since our attack belongs to intercept-and-resend attack (Eve measures all the signals and resend her prepared pulses to Bob), which corresponds to an entanglementbreaking channel and no secret key can be generated under this channel
Summary
Quantum key distribution (QKD) provides means for unconditional secure key transmission between two distant parties. We propose a hybrid measurement attack, with only linear optics, homodyne detection, and single photon detection, to the widely used vacuum 1 weak decoy state QKD system when the phase of source is partially randomized. In Ref. 15, Tang et al proposed and demonstrated an attack, based on a linear-optic unambiguous state discrimination measurement and PNS, to show that the security of a QKD system with nonrandom phase will be compromised. In Ref. 9, our group proposed an attack to show that the QKD system is still insecure even if the phase of source is partially randomized, but it is invalid for the widely used weak 1 vacuum decoy state method (their attack is only valid for the special one-decoy state method in some parameter regimes)
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