Attacking quantum key distribution with single-photon two-qubit quantum logic

Abstract

The Fuchs-Peres-Brandt (FPB) probe realizes the most powerful individual attack on BennettBrassard 1984 quantum key distribution (BB84 QKD) by means of a single controlled-NOT (CNOT) gate. This paper describes a complete physical simulation of the FPB-probe attack on polarizationbased BB84 QKD using a deterministic CNOT constructed from single-photon two-qubit quantum logic. Adding polarization-preserving quantum nondemolition measurements of photon number to this configuration converts the physical simulation into a true deterministic realization of the FPB attack.

Linear optical setups for active and passive quantum error correction in polarization encoded qubits

“…In order to maximize the amount of Re´nyi information about the error-free sifted bits that Bob receives for a given level of disturbance (probability to cause an error in a sifted bit), Eve has to choose properly the quantum state of her photon, the unitary transformation and the POVM she will use. It has been proved that the choices presented in figure 1 and in (1)-(5) are the optimal ones [9,10]:…”

“…This last case permits the construction of a passive system simplifying a lot its implementation. At last, we realize a security analysis of a single-photon quantum key distribution system, using the proposed quantum error correction setup, against the Fuchs-Peres-Brandt attack [9,10]. Basically, if true single-photons are used (hence photon number attack is not possible), the most general attack that can be realized by Eve consists of entangling the photon sent by Alice with another photon, provided by her, through a unitary operation.…”

Complete physical simulation of the entangling-probe attack on the Bennett-Brassard 1984 protocol

“…1, Eve supplies the target qubit to the cnot gate, which entangles it with the BB84 qubit that Alice is sending to Bob. Eve then makes her measurement of the target qubit to obtain information on the shared key bit at the expense of imposing detectable errors between Alice and Bob [5,6]. We have recently shown [6] that this Fuchs-PeresBrandt (FPB) entangling probe can be implemented using single-photon two-qubit (SPTQ) quantum logic in a proof-of-principle experiment.…”

“…Eve then makes her measurement of the target qubit to obtain information on the shared key bit at the expense of imposing detectable errors between Alice and Bob [5,6]. We have recently shown [6] that this Fuchs-PeresBrandt (FPB) entangling probe can be implemented using single-photon two-qubit (SPTQ) quantum logic in a proof-of-principle experiment. In SPTQ logic a single photon carries two independent qubits: the polarization and the momentum (or spatial orientation) states of the photon.…”

“…It is only a physical simulation because the two qubits of a single photon carrier must be measured jointly, so that Eve needs access to Bob's receiver, but not his measurement. The SPTQ probe could become a true attack if quantum nondemolition measurements were available to Eve [6]. Nevertheless, the physical simulation allows investigation of the fundamental security limit of BB84 against eavesdropping in the presence of realistic physical errors, and it affords the opportunity to study the effectiveness of privacy amplification when BB84 is attacked.…”