Digital signature system, and method

A signature method comprising:

• by a first apparatus:
• generating a first sketch using first biometric information of a user and a first signing key;
• generating first verification information based on the first signing key;
• and
• transmitting the first sketch and the first verification information to a third apparatus, the method comprising:
• by the second apparatus:
• generating a second sketch using second biometric information of the user and second signing key;
• generating second verification information based on the second signing key;
• and
• transmitting the second sketch and the second verification information to the third apparatus, the method comprising:
• by the third apparatus including a storage part that stores N (where N is an integer not less than 1) set(s) of the first sketch and the first verification information received from one or more instances of the first apparatus:
• on reception of the second sketch and the second verification information transmitted from the second apparatus,
• for the N set(s) of the first sketch and the first verification information stored in the storage part,
• restoring a difference key by using the first sketch of a kth set (where k is an integer not less than 1 and not more than N) and the second sketch;
• and
• identifying an ID (identification information), as a user ID, the ID corresponding to the kth set of the first sketch and the first verification information, wherein the first verification information of the kth set, the second verification information and the difference key restored by using the first sketch of the kth set and the second sketch satisfy a predetermined condition.

A user ID identification apparatus including at least a processor, a memory storing a program executable by the processor, and a communication interface, wherein the processor is configured to:

• receive a first sketch generated using first biometric information and a first signing key, and first verification information generated based on the first signing key and store a set of the first sketch and the first verification information in a storage part;
• receive a second sketch generated using second biometric information and second signing key, and second verification information generated based on the second signing key;
• restore a difference key using the first sketch stored in the storage and the second sketch, for one or more sets of the first sketch and the first verification information;
• and
• identify, an ID (identification information) corresponding to a set of the first sketch and the first verification information with a predetermined condition regarding the first verification information of the set, the second verification information, and the difference key being met, as a user ID.