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Conference on Lasers and Electro-Optics

Simple protocol of quantum cryptography based on two truly orthogonal states

Masato Koashi, N. Imoto

Published Nov 27, 2002• 0 citations
Publisher

Abstract

Summary form only given.One of the simplest protocols of quantum cryptography proposed so far is the one based on two nonorthogonal states. In this protocol, the receiver cannot determine every bit because there is no way to distinguish nonorthogonal states completely. Another simple protocol uses two orthogonal states, and the receiver can always discriminate between the two states that represent the bit values 0 and 1. In this protocol, however, the sender must mix the third states (vacuum states) in the bit stream to prevent eavesdropping. Thus the following question arises: do more simple protocols exist in which the sender switches between only two states and the receiver can obtain every bit value? Here we show that such a protocol does exist.

DOI
10.1109/iqec.1998.680188

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Summary form only given.One of the simplest protocols of quantum cryptography proposed so far is the one based on two nonorthogonal states. In this protocol, the receiver cannot determine every bit because there is no way to distinguish nonorthogonal states completely. Another simple protocol uses two orthogonal states, and the receiver can always discriminate between the two states that represent the bit values 0 and 1. In this protocol, however, the sender must mix the third states (vacuum states) in the bit stream to prevent eavesdropping. Thus the following question arises: do more simple protocols exist in which the sender switches between only two states and the receiver can obtain every bit value? Here we show that such a protocol does exist.
Since, in general, nonorthogonal states cannot be cloned, any eavesdropping attempt in a quantum-communication scheme using nonorthogonal states as carriers of information introduces some errors in the transmission, leading to the possibility of detecting the spy. Usually, orthogonal states are not used in quantum-cryptography schemes since they can be faithfully cloned without altering the transmitted data. Nevertheless, L. Goldberg and L. Vaidman [Phys. Rev. Lett. 75, 1239 (1995)] proposed a protocol in which, even if the data exchange is realized using two orthogonal states, any attempt to eavesdrop is detectable by the legal users. In this scheme the orthogonal states are superpositions of two localized wave packets traveling along separate channels. Here we present an experiment realizing this scheme.
Oblivious transfer between two untrusting parties is an important primitive in cryptography. There are different variants of oblivious transfer. In Rabin oblivious transfer, the sender Alice holds a bit, and the receiver Bob either obtains the bit, or obtains no information with probability p ? . Alice should not know whether or not Bob obtained the bit. We examine a quantum Rabin oblivious transfer (OT) protocol that uses two pure states. Investigating different cheating scenarios for the sender and for the receiver, we determine optimal cheating probabilities in each case. Comparing the quantum Rabin oblivious transfer protocol to classical Rabin oblivious transfer protocols, we show that the quantum protocol outperforms classical protocols, which do not use a third party, for some values of p ? . We find that quantum Rabin OT protocols that use mixed states can outperform quantum Rabin OT protocols that use pure states for some values of p ? . Published by the American Physical Society 2024
A setup for discriminating between arbitrary two coherent states of a single light mode with the highest success rate allowed by quantum mechanics is presented. Its application to time-multiplexed quantum key distribution is discussed. PACS numbers: 03.67.Dd, 42.50.\\Gammap, 03.65.Bz From the conceptual point of view, the simplest quantum protocol for establishing a cryptographic key is a transmission of a random sequence of two non-orthogonal states [1]. What makes this protocol secure, is the impossibility of discriminating between these two states with certainty. Thus, any attempt of eavesdropping inevitably generates noise in the transmission channel, which can be detected by the communicating parties [2]. A straightforward optical realisation of this protocol is the use of two weak coherent states in an interferometric setup [1,3]. In the two-state protocol, the cryptographic key is constructed from these events, for which the receiving party managed to identify unambiguously the o...
All existing quantum cryptosystems use nonorthogonal states as the carriers of information. Nonorthogonal states cannot be cloned (duplicated) by an eavesdropper. As a result, any eavesdropping attempt must introduce errors in the transmission, and, therefore, can be detected by the legal users of the communication channel. Orthogonal states are not used in quantum cryptography, since they can be faithfully cloned without altering the transmitted data. We present a cryptographic scheme based on orthogonal states, which also assures the detection of any eavesdropper.
A quantum key distribution (QKD) protocol based on constructed nonorthogonal states is proposed. By transmitting the photons from Bell states in random order the sender constructs nonorthogonal states, which can prevent an eavesdropper from extracting the key information. At the destination, the receiver performs Bell measurements and then obtains secure key. Different from previous nonorthogonal-states-based QKD protocols, our protocol exhibits a new feature, that is, the users can also obtain some key bits even when they choose different "bases"! Thus it can reach a higher efficiency in theory. Besides, we present a trade-off between the information that an eavesdropper can elicit and the corresponding error rate he/she would introduce, which shows that our protocol is secure.