We present a classification of quantum public-key encryption protocols. There are six elements in quantum public-key encryption: plaintext, ciphertext, public-key, private-key, encryption algorithm and decryption algorithm. According to the property of each element which is either quantum or classical, the quantum public-key encryption protocols can be divided into 64 kinds. Among 64 kinds of protocols, 8 kinds have already been constructed, 52 kinds can be proved to be impossible to construct and the remaining 4 kinds have not been presented effectively yet. This indicates that the research on quantum public-key encryption protocol should be focus on the existed kinds and the unproposed kinds.
We propose two interactive identification protocols based on a general construction of quantum public-key
cryptosystem. Basic protocol contains set-up phase and authentication phase. Participants do operation with
quantum computing of Boolean function in two-round transmission of authentication phase. Basic one only
ensures completeness and soundness, but leaks information about private-key. We modify basic protocol with
random string and random Boolean permutation. After modification, both transmitted states in two-round
transmission can be proved to be ultimate mixed states. No participant or attacker will get useful information
about private-key by measuring such states. Modified protocol achieves property of zero-knowledge.
The classification of quantum symmetric-key encryption protocol is presented. According to five elements of a
quantum symmetric-key encryption protocol: plaintext, ciphertext, key, encryption algorithm and decryption
algorithm, there are 32 different kinds of them. Among them, 5 kinds of protocols have already been constructed
and studied, and 21 kinds of them are proved to be impossible to construct, the last 6 kinds of them are not
yet presented effectively. That means the research on quantum symmetric-key encryption protocol only needs to
consider with 5 kinds of them nowadays.
We present an unconditionally secure quantum election scheme, which based on a distributed scheme to ensure
the privacy of the voters. The voting administrator is made up by two parties who cannot cooperate within a
certain period of time, and we use an”identity exchange”scheme to conceal the identity of voters. While the
election is completed, nobody except the voter himself can match him with his ballot even if the administrator
and the counter collaborate up to do so. The scheme can also work well with noisy and lossy quantum channels.
We investigate the definition of security for encryption scheme in quantum context. We systematically define the
indistinguishability and semantic security for quantum public-key and private-key encryption schemes, and for
computational security, physical security and information-theoretic security. Based on our definition, we present a
necessary and sufficient condition that leads to information-theoretic indistinguishability for quantum encryption
scheme. The equivalence between the indistinguishability and semantic security of quantum encryption scheme
is also proved.
All of the widely used public-key encryption schemes will not remain their security in the environment of quantum
computing. We present here two quantum public-key encryption protocols of classical message, and show
that they can achieve information-theoretical security owing to a new type structure of public-key encryption
algorithm.
We propose two definitions of quantum one-way transformation and quantum trapdoor one-way transformation
beyond computational hypothesis, and give four examples. Then, we present a general way to construct a
quantum public-key encryption scheme from a quantum one-way transformation and a quantum trapdoor oneway
transformation, and give a concrete example which is quantum-message-oriented. The security of this kind of
encryption schemes is based on the one-way property of quantum one-way transformation and quantum trapdoor
one-way transformation, and this kind of schemes is information-theoretically secure.
We attempt to develop Shannon's concept of the unicity distance into the quantum context. Based on the definition
of information-theoretic security for quantum cryptography, we present a quantum probabilistic encryption
algorithm with bounded information-theoretic security, and then work out its quantum unicity distances. The
result shows that quantum unicity distance is much bigger than the unicity distance of classical cryptography.
Relativistic quantum key distribution (QKD) protocol is a kind of modified BB84 QKD protocol based
on the principles of not only quantum mechanics but also special relativity. Its advantage compared with
BB84 protocol is that all of the qubits could be used for key generation, and Alice and Bob are able to select
any measuring bases. We prove its unconditional security against coherent attack via the method based on
CSS codes: begin with a modified EPR based protocol which can be proved unconditionally secure, then
reduce the protocol to a CSS codes based protocol. Finally, the CSS codes based protocol is demonstrated
equivalent to the relativistic QKD protocol, and we arrived at the conclusion of the unconditional security of
the final key.
Based on amplitude character of quantum Rabi oscillation driven by coherent field we show that there exists an
upper bound to logic complexity of quantum circuit. We introduce a parameter called single-qubit logic complexity and
estimate its decoherence limit in a reasonable case. The analysis show that a generally accepted constant threshold of
the threshold theorem limits the logic complexity to so small a number that even a typical construction of fault-tolerant
quantum Toffoli gate can hardly be implemented reliably. This result suggests that the construction of feasible
fault-tolerant quantum gates is still an arduous task.
Ekert91 protocol of quantum key distribution is an important protocol of key distribution that based on the quantum mechanics. According to it, we first discuss the variance functions of Bell inequality test and error rate comparison, and then define the sensitivities of two security strategies based on Bell inequality test and error rate comparison respectively. Finally we give out the eavesdropper's optimal attack strategy and compare the sensitivities of two security strategies.
Various protocols of quantum cryptography has been presented. Some of them can be used to transmit secret messages directly. In this letter we present a new kind of quantum cryptography protocol for direct transmission of classical and quantum messages based on Shamir's generic protocol on classical message encryption. Though Shamir's original idea has only realization of computational security and falls to middle-man attack, our protocol is theoretically secure based on properties of quantum entanglement and Boolean function, and can resist the middle-man attack.
We present a multi-photon scheme to improve the efficiency of free-space quantum key distribution system. Two essential features of free-space quantum key distribution system are its classical timing pulses and frequency tracking devices, we make use of these two features to design a new type of quantum key distribution system with multi-photon quantum signals and synchronously delayed classical signals. This scheme is much more efficient then the usual one, and in the same time, more secure since its synchronously randomizing of frequency and arriving time of quantum signals makes Eves have almost no opportunity to catch the quantum signals in time.
We present a multi-photon scheme to improve the efficiency of free-space quantum key distribution system. Two essential features of free-space quantum key distribution system are its classical timing pulses and frequency tracking devices, we make use of these two features to design a new type of quantum key distribution system with multi-photon quantum signals and synchronously delayed classical signals. This scheme is much more efficient then the usual one, and in the same time, more secure since its synchronously randomizing of frequency and arriving time of quantum signals makes Eves have almost no opportunity to catch the quantum signals in time.
Two essential features of free-space quantum key distribution system are its timing pulses and frequency tracking devices. We make use of these two features to design a new type of quantum key distribution system with synchronously delayed classical signals. This scheme is much more secure since its synchronously randomizing of frequency and arriving time of quantum signals makes Eves have almost no opportunity to catch the quantum signals in time. Besides, this scheme can improve the intrinsic photon utilization efficient from 50% to 100%. Because the scheme breaks the symmetry between Bob and Eve before open discussion, it extends the concept of quantum key distribution and increases our choice of protocol bases.
We present a quantum public-key cryptography protocol for quantum message transmission. The private key of this protocol includes three classical matrices: a generator matrix of a Goppa code, an invertible matrix and a permutation matrix. The public key is product of these three matrices. The encryption and decryption algorithms are merely quantum computations related with the transformations between bases of the quantum registers. The security of this protocol is based on the hypothesis that there is no effective algorithm of NP-complete problem.
We suggest here a two-point eavesdropping strategy aimed at a two nonorthogonal states protocol of quantum key distribution over a fiber-optic channel. When the single-photon sources and detectors of Alice, Bob and the two Eve are all ideal, the two-point attack can break the two nonorthogonal states protocol if the distance between Alice and Bob is longer than 30 km. However, Bennett's original multi-photon protocol is secure against both two-point and beam splitting attacks, though the protocol is realized with a weak pulsed source.
We present a new type of authentication scheme for quantum message based on algebraic coding theory and quantum computation operations between different quantum registers. The results are that if the pre-coding generator matrix in SN-S code is public, the quantum scheme is a public-key data integrity scheme; if it is secret, the quantum scheme is a hybrid data origin authentication scheme. The advantage of this scheme is that the public and secret keys are merely some classical data.
We present a new kind of quantum cryptography protocol based on Shamir's three-pass protocol of classical cryptography, which allows the transmission of qubits directly and secretly via the aid of an unjammable classical channel. In this protocol we implement the encryption and decryption transformations via rotations on the Poincare sphere of the photons polarization parameters. The key technique is that Bob's encryption rotation must be commutative with Alice s decryption rotation; this means that the axes of these two
rotations must be parallel. We also present a security analysis of the protocol under a man-in-the-middle attack.
We present a repeatable BB84 protocol for a hybrid quantum key distribution system based on the dual-velocity protocol and an error-correction scheme. This protocol is the first one that is immune to photon absorption, suitable for single-photon transmission and does not need any entanglement between photons.
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