User device for acquiring verifiable claims, system including said user device, and method for acquiring verifiable claims

1 . A user device comprising:

one or more processors; and

one or more memory devices configured to store one or more programs, wherein

the one or more programs, when executed by the one or more processors, cause the user device to function as:

a holding unit that holds confidential information;

a generation unit that generates a generator;

an arithmetic unit that calculates a commitment corresponding to the generator, on a basis of the generator and the confidential information;

an acquisition unit that transmits, to a first external device, an acquisition request including the generator and the commitment corresponding to the generator, to acquire a verifiable claim (VC) including the generator and the commitment corresponding to the generator; and

a presentation unit that presents a proof of the VC including a first value and a second value to a second external device, together with the VC that the acquisition unit has acquired, wherein

a value of the generator that the acquisition unit uses to newly acquire the VC is different from a value of the generator that the acquisition unit has used to acquire the VC in a past,

the arithmetic unit calculates the first value on a basis of the generator included in the VC presented by the presentation unit and a third value, and calculates the second value on a basis of a hash value of the first value, the third value, and a value corresponding to the confidential information, and

when the presentation unit presents a first VC to the second external device, and the presentation unit has presented the first VC to the second external device in a past, the arithmetic unit makes the third value to be used to calculate the first value and the second value different from the third value used when the first VC was presented to the second external device in the past.

2 . The user device according to claim 1 , wherein the arithmetic unit calculates an output value of a hash function having the value of the generator and a value corresponding to the confidential information as inputs, and calculates the commitment corresponding to the generator on a basis of the output value and the value of the generator.

3 . A system comprising: a user device; one or more first external devices; and one or more second external devices, wherein

the user device includes one or more processors and one or more memory devices configured to store one or more programs, the one or more programs, when executed by the one or more processors, causing the user device to function as:

a holding unit that holds confidential information;

a generation unit that generates a generator;

an arithmetic unit that calculates a commitment corresponding to the generator, on a basis of the generator and the confidential information; and

a first transmission unit that transmits, to at least one first external device of the one or more first external devices, an acquisition request including one or more generators and one or more commitments corresponding to each of the one or more generators to acquire one or more verifiable claims (VCs) corresponding to each of the one or more generators, and

a presentation unit that presents a proof of a VC including a first value and a second value to one second external device of the one or more second external devices, together with the VC acquired as a response to the acquisition request transmitted to the at least one first external device,

the one or more first external devices are configured to

transmit, to the user device, the one or more VCs, each VC including the generator and the commitment corresponding to the generator, and

the one or more second external devices are configured to determine whether a user of the user device is an owner of the VC on a basis of the generator and the commitment included in the VC and the proof, when the proof of the VC is presented together with the VC from the user device, wherein

values of the one or more generators included in the acquisition request to be transmitted by the first transmission unit to the at least one first external device are different from each other, and are different from values of the one or more generators included in the acquisition request that the first transmission unit has transmitted in a past, and

the first value is a value based on the generator included in the VC to be presented to the one second external device and a third value, and the second value is a value based on a hash value of the first value, the third value, and a value corresponding to the confidential information.

4 . A method in a user device,

the method comprising:

transmitting an acquisition request including one or more generators and one or more commitments corresponding to each of the one or more generators to a first external device, the one or more commitments having been generated on a basis of each of the one or more generators and confidential information held by the user device;

receiving, as a response to the transmitting the acquisition request, one or more verifiable claims (VCs) corresponding to each of the one or more generators from the first external device, each VC including the generator and the commitment corresponding to the generator;

transmitting, to a second external device, one VC of the one or more VCs and a proof corresponding to the one VC, wherein

values of the one or more generators included in the acquisition request are different from each other, and are different from values of the one or more generators included in the acquisition request that the user device has transmitted in a past, and

the proof corresponding to the one VC includes: a first value based on the generator included in the one VC and a random value; and a second value based on a hash value of the first value, the random value, and a value corresponding to the confidential information.