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Security aspects of practical quantum cryptography
 In Advances in Cryptology— EUROCRYPT2000 (2000
"... Abstract. The use of quantum bits (qubits) in cryptography holds the promise of secure cryptographic quantum key distribution schemes. Unfortunately, the implemented schemes are often operated in a regime which excludes unconditional security. We provide a thorough investigation of security issues f ..."
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Abstract. The use of quantum bits (qubits) in cryptography holds the promise of secure cryptographic quantum key distribution schemes. Unfortunately, the implemented schemes are often operated in a regime which excludes unconditional security. We provide a thorough investigation of security issues for practical quantum key distribution, taking into account channel losses, a realistic detection process, and modifications of the “qubits ” sent from the sender to the receiver. We first show that even quantum key distribution with perfect qubits might not be achievable over long distances when fixed channel losses and fixed dark count errors are taken into account. Then we show that existing experimental schemes (based on weak pulses) currently do not offer unconditional security for the reported distances and signal strength. Finally we show that parametric downconversion offers enhanced performance compared to its weak coherent pulse counterpart. 1
A Quick Glance at Quantum Cryptography
, 1998
"... The recent application of the principles of quantum mechanics to cryptography has led to a remarkable new dimension in secret communication. As a result of these new developments, it is now possible to construct cryptographic communication systems which detect unauthorized eavesdropping should it oc ..."
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Cited by 8 (2 self)
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The recent application of the principles of quantum mechanics to cryptography has led to a remarkable new dimension in secret communication. As a result of these new developments, it is now possible to construct cryptographic communication systems which detect unauthorized eavesdropping should it occur, and which give a guarantee of no eavesdropping should it not occur. Contents 1 Cryptographic systems before quantum cryptography 3 2 Preamble to quantum cryptography 7 Partially supported by ARL Contract #DAAL0195P1884, ARO Grant #P38804PH QC, and the LOOP Fund. 3 The BB84 quantum cryptographic protocol without noise 10 3.1 Stage 1. Communication over a quantum channel . . . . . . . 12 3.2 Stage 2. Communication in two phases over a public channel . 14 3.2.1 Phase 1 of Stage 2. Extraction of raw key . . . . . . . 14 3.2.2 Phase 2 of Stage 2. Detection of Eve's intrusion via error detection . . . . . . . . . . . . . . . . . . . . . . 15 4 The BB84 quantum cryptographic pr...
Cryptology Column  25 Years of Quantum Cryptography
, 1996
"... The fates of SIGACT News and Quantum Cryptography are inseparably entangled. The exact date of Stephen Wiesner's invention of "conjugate coding" is unknown but it cannot be far from April 1969, when the premier issue of SIGACT Newsor rather SICACT News as it was known at the timecame out. Muc ..."
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The fates of SIGACT News and Quantum Cryptography are inseparably entangled. The exact date of Stephen Wiesner's invention of "conjugate coding" is unknown but it cannot be far from April 1969, when the premier issue of SIGACT Newsor rather SICACT News as it was known at the timecame out. Much later, it was in SIGACT News that Wiesner's paper finally appeared [74] in the wake of the first author's early collaboration with Charles H. Bennett [7]. It was also in SIGACT News that the original experimental demonstration for quantum key distribution was announced for the first time [6] and that a thorough bibliography was published [19]. Finally, it was in SIGACT News that Doug Wiedemann chose to publish his discovery when he reinvented quantum key distribution in 1987, unaware of all previous work but Wiesner's [73, 5]. Most of the first decade of the history of quant
Dim Coherent States As Signal States In The Bb84 Protocol: Is It Secure?
"... Practical realizations of quantum key distribution employ dim coherent states as an approximation to single photon states. The advantage is that dim coherent states are convenient to use. The drawback is that the security proofs for quantum key distribution have to be adapted. Difficulties arising ..."
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Practical realizations of quantum key distribution employ dim coherent states as an approximation to single photon states. The advantage is that dim coherent states are convenient to use. The drawback is that the security proofs for quantum key distribution have to be adapted. Difficulties arising from the use of signal states containing multiphoton contributions in combination with lossy channels have been pointed out earlier by Huttner et al.. In this paper I describe a first numerical bound allowing quantum key distribution using dim coherent signal states in the presence of noise.
Effect of Channel Imperfection on the Secrecy Capacity of a Quantum Cryptographic System
"... A realistic quantum cryptographic system must function in the presence of noise and channel loss inevitable in any practical transmission. We examine the effects of these channel limitations on the security and throughput of a class of quantum cryptographic protocols known as fourstate, or BB84. Pr ..."
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A realistic quantum cryptographic system must function in the presence of noise and channel loss inevitable in any practical transmission. We examine the effects of these channel limitations on the security and throughput of a class of quantum cryptographic protocols known as fourstate, or BB84. Provable unconditional security against eavesdropping, which is the principal feature of quantum cryptography, can be achieved despite minor channel defects, albeit at a reduced transmission throughput. We present a semiempirical relation between the fullysecure throughput and the loss and noise levels in the channel. According to this relation, an implementation of BB84 utilizing commercially available detectors can reach throughputs as high as 10 4 10 5 secure bits per second over a practical channel of reasonable quality. KEYWORDS: quantum cryptography, security, channel capacity, secrecy capacity, optical networks. B. Slutsky, P. C. Sun, Y. Mazurenko, R. Rao, and Y. Fainman Page 3...
Quantum state discrimination
, 2008
"... It is a fundamental consequence of the superposition principle for quantum states that there must exist nonorthogonal states, that is states that, although different, have a nonzero overlap. This finite overlap means that there is no way of determining with certainty in which of two such states a ..."
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It is a fundamental consequence of the superposition principle for quantum states that there must exist nonorthogonal states, that is states that, although different, have a nonzero overlap. This finite overlap means that there is no way of determining with certainty in which of two such states a given physical system has been prepared. We review the various strategies that have been devised to discriminate optimally between nonorthogonal states and some of the optical experiments that have been performed to realise these.
Unconditional security at a low cost
, 2006
"... By simulating four quantum key distribution (QKD) experiments and analyzing one decoystate QKD experiment, we compare two data postprocessing schemes based on security against individual attack by Lütkenhaus, and unconditional security analysis by GottesmanLoLütkenhausPreskill. Our results sho ..."
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By simulating four quantum key distribution (QKD) experiments and analyzing one decoystate QKD experiment, we compare two data postprocessing schemes based on security against individual attack by Lütkenhaus, and unconditional security analysis by GottesmanLoLütkenhausPreskill. Our results show that these two schemes yield close performances. Since the Holy Grail of QKD is its unconditional security, we conclude that one is better off considering unconditional security, rather than restricting to individual attacks.
© 2010 Science Publications Quantum Cryptography with Several Cloning Attacks
"... Abstract: Problem statement: In a previous research, we investigated the quantum key distribution of the well known BB84 protocol with several intercept and resend attacks. In the present research, we studied the effect of many eavesdroppers cloning attacks of the BennettBrassard cryptographic prot ..."
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Abstract: Problem statement: In a previous research, we investigated the quantum key distribution of the well known BB84 protocol with several intercept and resend attacks. In the present research, we studied the effect of many eavesdroppers cloning attacks of the BennettBrassard cryptographic protocol on the quantum error and mutual information between honest parties and information with sender for each eavesdropper. Approach: The quantum error and the mutual information were calculated analytically and computed for arbitrary number of cloning attacks. Our objective in this study was to know if the number of the eavesdroppers and their angle of cloning act on the safety of information. Results: It was found that the quantum error and the secured/no secured transition depend strongly on the number of eavesdropper and their angle of attacks. The particular cases where all eavesdroppers collaborate were also investigated. Conclusion: Furthermore, the cloning attack’s quantum error is lower than the intercept and resends attacks one, which means that the cloning attacks is the optimal one for arbitrary number of eavesdropper.
ACHIEVING UNCONDITIONAL SECURITY BY QUANTUM CRYPTOGRAPHY
"... Classical cryptography algorithms are based on mathematical functions. The robustness of a given cryptosystem is based essentially on the secrecy of its (private) key and the difficulty with which the inverse of its oneway function(s) can be calculated. Unfortunately, there is no mathematical proof ..."
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Classical cryptography algorithms are based on mathematical functions. The robustness of a given cryptosystem is based essentially on the secrecy of its (private) key and the difficulty with which the inverse of its oneway function(s) can be calculated. Unfortunately, there is no mathematical proof that will establish whether it is not possible to find the inverse of a given oneway function. Since few years ago, the progress of quantum physics allowed mastering photons which can be used for informational ends and these technological progresses can also be applied to cryptography (quantum cryptography). Quantum cryptography or Quantum Key Distribution (QKD) is a method for sharing secret keys, whose security can be formally demonstrated. It aims at exploiting the laws of quantum physics in order to carry out a cryptographic task. Its legitimate users can detect eavesdropping, regardless of the technology which the spy may have. In this study, we present quantum cryptosystems as a tool to attain the unconditional security. We also describe the well known protocols used in the field of quantum cryptography. Keywords:quantum cryptogarphy,quantum key distribtuion, uncondtional security.
A Hamiltonian for Quantum Copying
, 1997
"... We derive an explicit Hamiltonian for copying the basis up and down states of a quantum twostate system—a qubit—onto n “copy ” qubits (n ≥ 1) initially all prepared in the down state. In terms of spin components, for spin 1 2 particle spin states, the resulting Hamiltonian involves n and (n + 1) ..."
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We derive an explicit Hamiltonian for copying the basis up and down states of a quantum twostate system—a qubit—onto n “copy ” qubits (n ≥ 1) initially all prepared in the down state. In terms of spin components, for spin 1 2 particle spin states, the resulting Hamiltonian involves n and (n + 1)spin interactions. The case n = 1 also corresponds to a quantumcomputing controlledNOT gate. PACS numbers: 03.65.Bz, 85.30.St. – 1 – Interest in quantum computing [127] has boosted studies of quantum mechanics of twostate systems such as the spin states of spin 1 2 particles. We will use “spin ” to indicate a twostate system in this context. The “binary ” up and down spin states are of particular significance and