114 results about "Alice and Bob" patented technology

Key management and user authentication systems and methods for quantum cryptography networks that allow for users securely communicate over a traditional communication link (TC-link). The method includes securely linking a centralized quantum key certificate authority (QKCA) to each network user via respective secure quantum links or “Q-links” that encrypt and decrypt data based on quantum keys (“Q-keys”). When two users (Alice and Bob) wish to communicate, the QKCA sends a set of true random bits (R) to each user over the respective Q-links. They then use R as a key to encode and decode data they send to each other over the TC-link.

Alice generates a sequence of key bits forming an initial cryptographic key. Alice then uses the sequence of key bits and a sequence of cipher bits to control respective control parameters of a quantum encoding process applied to a sequence of quantum pulses, where the sequence of cipher bits used is known to Bob. Alice then releases the encoded pulses towards Bob over a quantum channel. Bob uses the previously agreed-upon sequence of cipher bits to control a control parameter, such as the quantum basis, of a quantum detection process applied to the pulses received from Alice, thus producing a detection outcome for each received pulse. Bob then derives a final cryptographic key from the detection outcomes. Because the cipher bits used to select the quantum bases used by both Alice and Bob are known by both parties, the method allows the final cryptographic key to be distributed with full basis alignment compared to 50% for BB84, thus allowing efficient quantum key distribution over multiple hops.

Systems and methods for quantum secret splitting based on non-orthogonal multi-particle states are disclosed. The method includes preparing at a sender (“Charlie”) two qubits each of which can be in one of two non-orthogonal states and distributing the qubits to respective parties Alice and Bob. The method also includes measuring at Alice the state of the qubit she receives by a projective measurement so that the measurement result is either 0 or 1, and at Bob measuring the state of the qubit he receives such that the measurement result is either 0, 1 or ƒ, wherein ƒ represents a failure by Bob to properly measure the qubit state. The method also includes communicating between Alice, Bob and Charlie the outcome of their respective measurements so as to deduce the state of the qubits sent to Alice and Bob.

The quantum key distribution (QKD) systems (200, 300, 400) of the invention includes first and second QKD stations (Alice and Bob) according to the present invention, wherein either one or both QKD stations include fast optical switches (120, 220, 310, 320). Each fast optical switch is respectively optically coupled to two different round-trip optical paths (OP1 and OP2 at Alice, OP3 and OP4 at Bob) of different length that define respective optical path differences OPD_A and OPD_B, wherein OPD_A=OPD_B. By switching the fast optical switches using timed switching signals (S1-S3 at Alice, S4-S6 at Bob) from their corresponding controllers (CA at Alice, CB at Bob), the quantum signals—which can be single-photon or weak-coherent pulses—can be generated from a single optical pulse (112), randomly selectively encoded while traversing the optical paths in Alice and Bob, and then interfered and measured (detected) at Bob. The QKD system has less loss as compared to conventional fiber-based QKD systems because it omits at least some of the beamsplitters in conventional QKD systems.

Entanglement-based QKD systems and methods with active phase tracking and stabilization are disclosed. The method includes generating in an initial state-preparation stage (Charlie) pairs of coherent photons (P1) at a first wavelength. Second harmonic generation and spontaneous parametric downconversion are used to generate entangled pairs of photons (P5) having the first wavelength—State detection stages (Alice and Bob) optically coupled to Charlie receive respective entangled photons from Charlie. The relative phase delays of the entangled photons are tracked using reference optical signals (P3) generated by Charlie and having the same wavelength as the entangled photons. Classical detectors (132A, 132B) detect the reference signals while single-photon detectors (130A, 130B) and a control unit (control unit C) generates an phase-correction signal that maintains the relative phases of the three phase delay loops (40, 100A,100B ) via adjustable phase-delay elements (MA, MB).

A method for enhancing the security of a quantum key distribution (QKD) system having QKD stations Alice and Bob. The method includes encrypting key bits generated by a true random number generator (TRNG) and sent to a polarization or phase modulator to encode weak optical pulses as qubits to be shared between Alice and Bob. Key bit encryption is achieved by using a shared password and a stream cipher. Bob obtains at least a subset of the original key bits used by Alice by utilizing the same stream cipher and the shared password.

The invention relates to a blind verifiable cryptographic signature method based on a block chain. The method includes three parties: a signer Alice, a signature extractor Bob, and a block chain verifier. The method is implemented in the following steps: Alice and Bob negotiate a message to be signed and generate their own key pairs respectively according to system parameters; Alice and Bob generate signature tags; Alice generates a blind verifiable cryptographic signature that matches the signature tag; the block chain verifier verifies the validity of the cryptographic verifiable cryptographic signature; and Bob extracts a digital signature from the blind verifiable cryptographic signature. The method can be used to construct a fair digital signature exchange protocol that protects privacy in a public block chain environment. The method blindens the public key information of the signer so that a node on a block chain cannot obtain the real digital signature and the public key of the signer aside from verifying the validity of the signature, and the privacy protection for the signer is achieved.

Methods are described for two parties to use a small shared secret (S) to mutually authenticate one another other over an insecure network. The methods are secure against off-line dictionary attack and incorporate an otherwise unauthenticated public key distribution system. One embodiment uses two computers Alice and Bob, and a Diffie-Hellman exponential key exchange in a large prime-order finite group. Both parties choose the same generator of the group (g) as a function of S. Alice chooses a random number R_A, and sends g^{R<sub2>A </sub2>}to Bob. Bob chooses a random R_B, sends g^{R<sub2>B </sub2>}to Alice. Both compute a shared key K=g^{(R<sub2>A</sub2>R<sub2>B</sub2>)}. Each party insures that K is a generator of the group, verifies that the other knows K, and then uses K as an authenticated key. Constraints are described to prevent passive and active attacks. An extension is described where Alice proves knowledge of S to Bob who knows only a one-way transformation of S. These methods establish a secure, authenticated network session using only an easily memorized password.

A method of autocalibrating the timing of the laser (202) in a quantum key distribution (QKD) system (200) is disclosed. Laser (202) generates photon signals (204) in response to a laser gating signal (S0) from a controller (248). The method includes first performing a laser gate scan (304) to establish the optimum arrival time (T_MIN) of the laser gating signal corresponding to an optimum (e.g., minimum) bit-error rate BER (e.g., BER_MIN) when exchanging photon signals between encoding stations (Alice and Bob) of the QKD system. Once the optimum laser gating signal arrival time (T_MIN) is determined, the laser gate scan is terminated (306) and a laser gate dither process (308) is initiated. The laser gate dither involves varying the arrival time (T) of the laser gating signal around the optimum value of the arrival time T_MIN. The laser gate dither provides minor adjustments to the laser gating signal arrival time to ensure that the system operates at or near the optimum BER.

The invention relates to a multi-hop lossless teleportation method based on a non-maximum entangled chain channel. Alice and Bob, which do not directly share a quantum entanglement pair at the beginning, continuously carry out entanglement exchange through the help of p middle nodes; finally, a quantum entanglement channel is constructed; and the multi-hop teleportation process of the sender Alicetransmitting a single-particle multi-energy level unknown quantum state to the receiver Bob is completed. The method in the invention uses the non-maximum entangled chain channel; even the sender andthe receiver do not directly share the quantum entanglement pair, the quantum state information can be still transmitted between both the sides; and the requirement for constructing a complex quantumcommunication network can be satisfied; in the multi-hop lossless teleportation system in the invention, if the teleportation process is successfully executed, the information receiver Bob can obtainthe transmitted quantum state information; if the teleportation process fails, the information sender Alice can restore the transmitted unknown quantum state information; and the unknown quantum state information is not lost.

The invention discloses a quantum key agreement protocol based on GHZ state, comprising the following steps that: step 1, Alice and Bob randomly generate respective classical keys; step 2, Alice prepares the GHZ state and divides all particles into sequences, inserts decoy photons into one of the sequences and then transmits the sequence to Bob; step 3, Bob measures the decoy photons, Alice calculates an error rate, if the error rate is low, a step 4 is executed, otherwise, the step 2 is executed again; step 4, Alice and Bob respectively perform measurement and obtain the measurement result of each other; step 5, Alice executes unitary transformation and obtains a new sequence, and Alice transits the sequence with the inserted decoy photons to Bob; step 6, Bob measures the decoy photons, and Alice calculates the error rate, if the error rate is low, a step 7 is executed, and otherwise, the step 2 is executed again; step 7, Alice calculates a shared key of both sides; step 8, Bob generates the shared key. The quantum key agreement protocol based on GHZ state can resist participant attack, outside attack and Trojan horse attack. The quantum key agreement protocol based on GHZ state is safe in both a noiseless quantum channel and a quantum noisy channel. Moreover, quantum bit efficiency of the quantum key agreement protocol based on GHZ state is higher than the existing protocols.

The invention discloses a controlled quantum security direct communication method based on four particle cluster states. Alice and Bob respectively serve as a legal information sender and a legal information receiver during a quantum communication process, and Charlie serves as a credible scheme control party; information security is achieved by randomly inserting a single photon to perform measurement-based comparison detection, and communication starts after security detection; Alice uniformly divides the prepared four particle cluster states into two groups, after being subjected to an XOR operation with a pseudorandom sequence, the sent information is encoded on the two particles reserved by Alice via unitary transformation. Alice performs Bell-based measurement on reserved particles, and sends measurement information to Bob, and Bob recovers the original sequence via an initial state sent by Charlie after the measurement information is compared. The four particle cluster states used by the method has good entanglement, connectivity and damage resistance, only the receiver Bob in the method gets the permission of the controller Charlie, Bob can recover the original information, so that the information can be effectively prevented from being attacked during a transmission process, and an implementation process is simple.

The invention relates to a GHZ-state-based joint remote M-bit W state preparation method, which is designed to utilize least quantum channel resources. The method comprises the following steps that: two senders, namely, Alice and Bob as well as one receiver, namely, Charlie remotely prepare an M-bit W state, the three parties only need to share [log<2>M] GHZ channels, and the sender, namely, Alicepreprocesses a quantum communication channel according to amplitude information of the W state; the two senders, namely, Alice and Bob respectively construct corresponding measurement bases accordingto partial phase information of the W state to be prepared, measure own particles, and send measurement results to the receiver, namely, Charlie; the receiver, namely, Charlie performs a unitary operation on owned particles according to the measurement results of the two senders, namely, Alice and Bob to obtain an intermediate quantum state corresponding to a target W state; and the receiver, namely, Charlie introduces auxiliary particles, performs a corresponding substitution operation, and recovers a target M-bit W state. Through adoption of the method, information leakage can be avoided, and the consumption of quantum resources is reduced effectively.

The invention discloses a four-particle GHZ state-based two-party quantum key agreement protocol. The protocol includes the following steps that: step 1, Alice and Bob randomly generate respective classic keys and negotiate on functions; step 2, Alice selects n four-particle GHZ combination and separation sequences, and randomly inserts decoy photons into three sequences and transmits the new sequences to Bob; step 3, Bob measures the decoy photons, and Alice calculates an error rate; step 4, Alice executes CNOT operation on every three corresponding particles with the same serial numbers in the sequences by twice; step 5, Alice executes unitary transformation so as to obtain new sequences, and selects out the decoy photons and inserts the decoy photons into the sequences and transmits the sequences to Bob; step 6, Bob measures the decoy photons; Alice compares measurement results and calculates an error rate, and step 7 is executed if the error rate is low, otherwise, the method returns to step 2; step 7, Alice generates a shared key; and step 8, Bob generates a shared key. With the four-particle GHZ state two-party quantum key agreement protocol of the invention adopted, existing participant attacks and the external attacks can be resisted. The quantum bit efficiency of the protocol is much higher than that of an existing protocol.

The invention discloses an ECDSA digital signature method based on two-party collaboration. The method comprises the following steps: step 1), respectively generating corresponding signature public and private key pairs and other parameters by a signature party Alice and a signature party Bob participating in the collaborative signature; and step 2), collaboratively completing ECDSA signature by Alice and Bob, and finally outputting the signature (r,s). According to the ECDSA digital signature method based on the two-party collaboration provided by the invention, under the premise of ensuringthe security and the correctness, a signature process does not introduce high-overhead password operations such as homomorphic encryption, oblivious transfer and the like, so that a signature scheme achieves a good balance between the communication overhead and the computation overhead, and therefore the performance is remarkably superior to that of all existing ECDSA two-party collaborative digital signature methods.

The invention discloses a remote teleportation method based on a four-bit Cluster state. For network terminal users Alice and Bob, through help of an intermediate node, communication between a networkterminal Alice and the other terminal user Bob is completed. The method comprises the four steps that 1, the four-bit most entangled Cluster state is shared by the terminal users Alice, Bob and the intermediate node Li (i=1, 2, 3, ..., p), and a quantum entanglement channel of the terminal users Alice and Bob and the intermediate node Li (i=1, 2, 3, ..., p) is built; 2, modulation and measurementare conducted, wherein CZ operation is conducted on corresponding particles by the terminal user Alice and the intermediate node Li, moreover, Bell measurement is conducted on the particles in handsby the intermediate node, and measurement results are announced; 3, a direct quantum channel between the terminal user Alice/Bob and the other terminal user Bob/Alice is built according to the Bell measurement results of the intermediate node through unitary operation; 4, according to difference of information transferring modes, the terminal users Alice and Bob choose corresponding restoring operation according to the Bell measurement results of each other to achieve intercommunication.

The present invention discloses a two-party quantum key negotiation protocol based on a three-particle GHZ state, comprising the following steps: step 1: Alice and Bob negotiate codes of quantum states; step 2: Alice prepares n+q GHZ states and divides all the particles into sequences; Alice sends a sequence SC to Bob; step 3: Bob selects and measures q sample particle(s); Alice selects measurement bases to measure corresponding particles; Bob calculates an error rate; and if the error rate is low, step 4 is performed, otherwise step 2 is performed; step 4: Alice performs a Bell measurement on two particles with the same sequence number in the sequences; Bob performs X-base measurement on the particles in the sequences; and Alice and Bob respectively obtain the same shared key according to measurement results and the codes of the quantum states. According to the present invention, the two-party quantum key negotiation protocol can resist existing participant attacks and external attacks as well as Trojan horse attacks, is safe in noiseless quantum channels and quantum noise channels, and can achieve a relatively high quantum bit efficiency.

The invention discloses a four-particle cluster state multi-hop stealth transfer method based on a non-maximum entanglement cluster state. A source node Alice and a target node Bob realize long-distance quantum communication between Alice and Bob through the help of an intermediate node. The method mainly comprises four steps that (1) a source node Alice, a target node Bob and an intermediate nodeshare a non-maximum entanglement cluster state, and a quantum entanglement channel is established; (2) Alice and an intermediate node carry out CZ operation on particle pairs in hands of the Alice and the intermediate node, and modulate a channel; (3) the Alice and the intermediate node perform Bell measurement on the particle pairs in their hands and inform the measurement result, and the Aliceestablishes a direct quantum channel with the Bob through unitary operation; and (4) the Alice performs Bell-based measurement on the particle pairs in the hand, and Bob performs a series of unitary operations according to the measurement result of the Alice to obtain a transmitted unknown quantum state. The information transmission efficiency is high, the long-distance remote quantum communication problem can be solved through the help of the intermediate nodes, and the requirement for constructing a complex quantum communication network can be met.

The invention discloses a cross-medium equipment-independent and discrete modulation continuous variable quantum key distribution system. An eight-state quantum state is prepared by a trusted intermediate party through discrete modulation, the eight-state quantum state is sent to Alice and Bob after photon subtraction, Alice and Bob perform demodulation and homodyne detection on the received quantum state respectively, and a security key is established within an effective distance. According to the invention, a continuous variable quantum key distribution technology in a free space is improved, and the quantum state is prepared and sent by the trusted intermediate party, so that the system has equipment independence, and the communication security is ensured; the photon subtraction operation can improve the entanglement degree between the quanta so as to improve the transmission distance; the homodyne detection can effectively filter the interference of the outside on the optical signal, and the detection result can be well obtained even if the optical signal is influenced to a certain extent. The scheme is oriented to equipment independence under an air-water channel, discrete modulation continuous variable quantum key distribution is utilized, and more practicability is brought to free space communication of quanta.