Patent ID: 7035411

Claim:
A computer-implemented encryption method comprising: an acquisition step of inputting arbitrary quantum information and acquiring information of a quantum two-state system as a qubit by performing a computation based on a physical system; a first encryption step of encrypting the qubit acquired in the acquisition step; an adding step of adding to the encrypted qubit a quantum state having signature information for guaranteeing that the qubit is really transferred from a sender to a recipient to produce encrypted and signature-containing qubits; a second encryption step of encrypting the encrypted and signature-containing qubits; a sending step of sending the quantum state obtained in the second encryption step to the recipient; and a measurement step of determining that a quantum state is really received by examining whether a qubit carrying encrypted and signature-containing quantum information is present, wherein a sender and a recipient perform cryptographic communication procedures by using a classical channel, through which classical information (bit string) is transmitted, the information that is transmitted is disclosed to allow an eavesdropper to know the information, and the eavesdropper can copy the information but cannot alter or erase the information, and a quantum channel, through which quantum information (qubit string) is transmitted, and the eavesdropper can steal, observe, and alter part of all of a quantum state that is transmitted, but cannot clone an arbitrary quantum state, the quantum state obtained in the second encryption is sent to the recipient through the quantum channel, upon reception of the quantum state, the recipient disconnects the quantum channel and notifies the sender of the corresponding quantum state through the classical channel, upon reception of the notification from the recipient, the sender notifies the recipient of which type of transformation encrypting operation in the second encryption step is through the classical channel, the recipient performs inverse transformation to the operation in the second encryption step notified from the sender, observes a qubit representing a signature, and notifies the sender of the result through the classical channel, the sender receives the signature from the recipient, examines whether the signature is correct, and if the signature is correct, notifies the recipient of which type of transformation the first encrypting operation is through the classical channel, or if the signature is not correct, ends the communication upon determining that an eavesdropper has intervened, and the recipient obtains final quantum information by performing inverse transformation to the first encrypting operation with respect to the received quantum state.