Optimal eavesdropping on quantum key distribution without quantum memory (original) (raw)

Extended analysis of the Trojan-horse attack in quantum key distribution

2018

The discrete-variable quantum key distribution protocols based on the 1984 protocol of Bennett and Brassard (BB84) are known to be secure against an eavesdropper, Eve, intercepting the flying qubits and performing any quantum operation on them. However, these protocols may still be vulnerable to side-channel attacks. We investigate the Trojan-horse side-channel attack where Eve sends her own state into Alice's apparatus and measures the reflected state to estimate the key. We prove that the separable coherent state is optimal for Eve among the class of multimode Gaussian attack states, even in the presence of thermal noise. We then provide a bound on the secret key rate in the case where Eve may use any separable state.

OPTIMAL EAVESDROPPING ON NOISY STATES IN QUANTUM KEY DISTRIBUTION

International Journal of Quantum Information, 2009

We study eavesdropping in quantum key distribution with the six state protocol, when the signal states are mixed with white noise. This situation may arise either when Alice deliberately adds noise to the signal states before they leave her lab, or in a realistic scenario where Eve cannot replace the noisy quantum channel by a noiseless one. We find Eve's optimal mutual information with Alice, for individual attacks, as a function of the qubit error rate. Our result is that added quantum noise can make quantum key distribution more robust against eavesdropping.

No-signaling Quantum Key Distribution: A Straightforward Approach

arXiv (Cornell University), 2012

We outline a straightforward approach for obtaining a secret key rate using only no-signaling constraints. Assuming an individual attack, we consider all possible joint probabilities. First we suppose temporarily that Eve (an eavesdropper) is restricted to binary outcomes. We impose constraints due to the no-signaling principle and given measurement outcomes. Within the remaining space of joint probabilities, by using convex optimization, we find the maximum mutual information IBEmax(2)I_{BE}^{max}(2)IBEmax(2) between Bob (a user) and a binary-restricted Eve. Then, by considering a certain coarse graining mapping, we show how to get a bound on IBEmaxI_{BE}^{max}IBEmax, the maximal mutual information between Bob and Eve, whose number of outcomes is not restricted, from the quantity IBEmax(2)I_{BE}^{max}(2)IBEmax(2). Using the Csiszár-Körner formula and the calculated bound, we obtain the key generation rate.

The security of practical quantum key distribution

Reviews of Modern Physics, 2009

Quantum key distribution ͑QKD͒ is the first quantum information task to reach the level of mature technology, already fit for commercialization. It aims at the creation of a secret key between authorized partners connected by a quantum channel and a classical authenticated channel. The security of the key can in principle be guaranteed without putting any restriction on an eavesdropper's power. This article provides a concise up-to-date review of QKD, biased toward the practical side. Essential theoretical tools that have been developed to assess the security of the main experimental platforms are presented ͑discrete-variable, continuous-variable, and distributed-phase-reference protocols͒.

Security Bounds for Efficient Decoy-State Quantum Key Distribution

IEEE Journal of Selected Topics in Quantum Electronics, 2015

Information-theoretical security of quantum key distribution (QKD) has been convincingly proven in recent years and remarkable experiments have shown the potential of QKD for real world applications. Due to its unique capability of combining high key rate and security in a realistic finite-size scenario, the efficient version of the BB84 QKD protocol endowed with decoy states has been subject of intensive research. Its recent experimental implementation finally demonstrated a secure key rate beyond 1 Mbps over a 50 km optical fiber. However the achieved rate holds under the restrictive assumption that the eavesdropper performs collective attacks. Here, we review the protocol and generalize its security. We exploit a map by Ahrens to rigorously upper bound the Hypergeometric distribution resulting from a general eavesdropping. Despite the extended applicability of the new protocol, its key rate is only marginally smaller than its predecessor in all cases of practical interest.

Performance of two quantum-key-distribution protocols

Physical Review A, 2006

We compare the performance of Bennett-Brassard 1984 ͑BB84͒ and Scarani-Acin-Ribordy-Gisin 2004 ͑SARG04͒ protocols, the latter of which was proposed by V. Scarani et al. ͓Phys. Rev. Lett. 92, 057901 ͑2004͔͒. Specifically, in this paper, we investigate the SARG04 protocol with two-way classical communications and the SARG04 protocol with decoy states. In the first part of the paper, we show that the SARG04 scheme with two-way communications can tolerate a higher bit error rate ͑19.4% for a one-photon source and 6.56% for a two-photon source͒ than the SARG04 one with one-way communications ͑10.95% for a onephoton source and 2.71% for a two-photon source͒. Also, the upper bounds on the bit error rate for the SARG04 protocol with two-way communications are computed in a closed form by considering an individual attack based on a general measurement. In the second part of the paper, we propose employing the idea of decoy states in the SARG04 scheme to obtain unconditional security even when realistic devices are used. We compare the performance of the SARG04 protocol with decoy states and the BB84 one with decoy states. We find that the optimal mean-photon number for the SARG04 scheme is higher than that of the BB84 one when the bit error rate is small. Also, we observe that the SARG04 protocol does not achieve a longer secure distance and a higher key generation rate than the BB84 one, assuming a typical experimental parameter set.

Security of Quantum Key Distribution Protocols

InTech eBooks, 2018

Quantum key distribution (QKD), another name for quantum cryptography, is the most advanced subfield of quantum information and communication technology (QICT). The first QKD protocol was proposed in 1984, and since then, more protocols have been proposed. It uses quantum mechanics to enable secure exchange of cryptographic keys. In order to have high confidence in the security of the QKD protocols, such protocols must be proven to be secure against any arbitrary attacks. In this chapter, we discuss and demonstrate security proofs for QKD protocols. Security analysis of QKD protocols can be categorised into two techniques, namely infinite-key and finite-key analyses. Finite-key analysis offers more realistic results than the infinite-key one, while infinite-key analysis provides more simplicity. We briefly provide the background of QKD and also define the basic notion of security in QKD protocols. The cryptographic key is shared between Alice and Bob. Since the key is random and unknown to an eavesdropper, Eve, she is unable to learn anything about the message simply by intercepting the ciphertext. This phenomenon is beyond the ability of classical information processing. We then study some tools that are used in the derivation of security proofs for the infinite-and finite-length key limits.

Finite key analysis for symmetric attacks in quantum key distribution

Physical Review A, 2006

We introduce a constructive method to calculate the achievable secret key rate for a generic class of quantum key distribution protocols, when only a finite number n of signals is given. Our approach is applicable to all scenarios in which the quantum state shared by Alice and Bob is known. In particular, we consider the six state protocol with symmetric eavesdropping attacks, and show that for a small number of signals, i.e. below n ∼ 10 4 , the finite key rate differs significantly from the asymptotic value for n → ∞. However, for larger n, a good approximation of the asymptotic value is found. We also study secret key rates for protocols using higher-dimensional quantum systems.