Search execution device, search execution method, computer readable medium and searchable encryption system

A search execution method comprising:

• receiving a trapdoor generated based on a user secret key in which a search auxiliary key and an attribute of a user are set and a search keyword, together with a key identifier (ID) that identifies the search auxiliary key;
• decrypting an encrypted tag in which an attribute of a user who is allowed retrieval and a search word are set, using the trapdoor and the search auxiliary key indicated by the key ID, so as to identify a tag that is retrievable for the attribute set in the user secret key and contains a search word corresponding to the search keyword;
• deleting the search auxiliary key indicated by the key identifier (ID) when the user secret key is revoked;
• and
• disabling identification of the tag using the user secret key without re-encrypting the encrypted tag, based on the deletion of the search auxiliary key and an association of the search auxiliary key with the user secret key by the key identifier (ID).

A non-transitory computer readable medium storing a search execution program that causes a computer to function as a search execution device to perform:

• a search request receiving process of receiving a trapdoor generated based on a user secret key in which a search auxiliary key and an attribute of a user are set and a search keyword, together with a key identifier (ID) that identifies the search auxiliary key;
• a search executing process of decrypting an encrypted tag in which an attribute of a user who is allowed retrieval and a search word are set, using the trapdoor received by the search request receiving process and the search auxiliary key indicated by the key ID received by the search request receiving process, so as to identify a tag that is retrievable for the attribute set in the user secret key and contains a search word corresponding to the search keyword;
• and
• a search privilege revocation process of:
• deleting the search auxiliary key indicated by the key identifier (ID) when the user secret key is revoked, and
• disabling identification of the tag using the user secret key without re-encrypting the encrypted tag, based on the deletion of the search auxiliary key and an association of the search auxiliary key with the user secret key by the key identifier (ID).

A searchable encryption system comprising:

• a key generation device comprising processing circuitry to generate a search auxiliary key and a user secret key in which the search auxiliary key and an attribute of a user are set;
• an access terminal to generate a trapdoor based on the user secret key generated by the key generation device and a search keyword;
• a search execution device comprising processing circuitry to decrypt an encrypted tag in which an attribute of a user who is allowed retrieval and a search word are set, using the trapdoor generated by the access terminal and the search auxiliary key, so as to identify a tag that is retrievable for the attribute set in the user secret key and contains a search word corresponding to the search keyword, wherein
• the processing circuitry of the search execution device:
• deletes the search auxiliary key indicated by a key identifier (ID) when the user secret key is revoked, and
• disables identification of the tag using the user secret key without re-encrypting the encrypted tag, based on the deletion of the search auxiliary key and an association of the search auxiliary key with the user secret key by the key identifier (ID).