[Claim 1] A secret search system comprising:
a management device including
an encryption similarity calculation unit to calculate, by performing a
homomorphic operation on storage encryption data being storage data encrypted using a homomorphic encryption, and search encryption data being search data encrypted using the homomorphic encryption, the search data being used in search of the storage data, an encryption similarity which is a similarity degree between the storage data and the 10 search data being encrypted using the homomorphic encryption, and
an encryption result transmission unit to generate an encryption search result to
represent whether or not the similarity degree is not more than a threshold value by
using the encryption similarity, and to transmit the encryption search result generated,
and
a search device including
a decryption unit to decrypt the encryption search result transmitted from the management device, and to output the encryption search result decrypted as a search result, and
an output unit to output search result information to represent whether the 20 similarity degree is not more than the threshold value or not, based on the search result.
[Claim 2] The secret search system as defined in claim 1,
wherein the encryption result transmission unit includes:
a similar ciphertext generation unit to generate a plurality of similar ciphertexts, which are a plurality of plaintexts being respectively encrypted using the homomorphic

encryption, me plurality ot plaintexts oemg similar to tne similarity degree, wnerem at least one of the plurality of plaintexts is 0 when the similarity degree is not more than the threshold value,
a plaintext randomization unit to randomize the plurality of plaintexts of the plurality of similar ciphertexts, and generate an assembly of random ciphertexts wherein the plurality of plaintexts randomized are respectively encrypted using the homomorphic encryption, and
a result transmission unit to generate the encryption search result, by using the assembly of the random ciphertexts generated by the plaintext randomization unit, and to transmit the encryption search result generated.
[Claim 3] The secret search system as defined in claim 2,
wherein the plaintext randomization unit randomizes a plaintext whose value is not 0 of the plurality of plaintexts while letting a plaintext whose value is 0 of the plurality of plaintexts be 0, and generates the assembly of the random ciphertexts wherein the plurality of plaintexts randomized are respectively encrypted using the homomorphic encryption, and
wherein the output unit, based on the search result, judges whether a plaintext whose value is 0 exists or not in the plurality of plaintexts, and when the plaintext whose value is 0 is judged to exist, outputs the search result information to represent that the similarity degree is not more than the threshold value, and when the plaintext whose value is 0 is judged not to exist in the plurality of plaintexts, outputs the search result information to represent that the similarity degree is larger than the threshold value.

[Claim 4] The secret search system as defined in claim 3,
wherein the similar ciphertext generation unit generates, when the similarity degree is not more than the threshold value, the plurality of similar ciphertexts which are the plurality of plaintexts, wherein a value-of-similarity-degree-numbered plaintext from a top is 0, respectively encrypted using the homomorphic encryption,
and wherein the output unit obtains, when the plaintext whose value is 0 is judged to exist in the plurality of plaintexts, an order of the plaintext whose value is 0 in the plurality of plaintexts, identifies the order as the similarity degree, and outputs the similarity degree identified.
[Claim 5] The secret search system as defined in claim 2 or claim3,
wherein the result transmission unit includes
a ciphertext disruption unit to disrupt the assembly of the random ciphertexts generated by the plaintext randomization unit, and to generate the assembly of the random ciphertexts disrupted as a disruption random ciphertext, and
a transmission unit to transmit the assembly of the disruption random ciphertext generated by the ciphertext disruption unit as the encryption search result,
and wherein the output unit judges whether a plaintext whose value is 0 exists in the plurality of the plaintexts, and when the plaintext whose value of 0 is judged to exist, outputs the search result information to represent that the similarity degree is not more than the threshold value, and when the plaintext whose value is 0 is judged not to exist, outputs the search result information to represent that the similarity degree is larger than the threshold value.
[Claim 6] The secret search system as defined in claim 5,

wherein the ciphertext disruption unit disrupts, in the assembly of the random ciphertexts, the assembly of the random ciphertexts by changing an order of the random ciphertexts in the assembly of the random ciphertexts, and generates the assembly of the random ciphertexts whose order is changed as a disruption random ciphertext.
[Claim 7] The secret search system as defined in claim 5,
wherein the ciphertext disruption unit disrupts the assembly of the random ciphertexts by replacing, in two random ciphertexts in the assembly of the random ciphertexts, a component of one random ciphertext with a component of the other random ciphertext, and generates the assembly of the random ciphertexts disrupted as the disruption random ciphertext.
[Claim 8] The secret search system as defined in claim 5,
wherein the ciphertext disruption unit disrupts the assembly of the random ciphertexts by combining all random ciphertexts included in the assembly of the random ciphertexts using a homomorphic multiplication, and generates one combination ciphertext which is made by combining the assembly of the random ciphertexts as the disruption random ciphertext.
[Claim 9] A management device comprising:
an encryption similarity calculation unit to calculate, by performing a homomorphic operation on storage encryption data being storage data encrypted using a homomorphic encryption, and search encryption data being search data encrypted using the homomorphic encryption, the search data being used in search of the storage data, an encryption similarity which is a similarity degree between the storage data and the

search data being encrypted using the homomorphic encryption;
a similar ciphertext generation unit to generate a plurality of similar ciphertexts, which are a plurality of plaintexts respectively being encrypted using the homomorphic encryption, the plurality of plaintexts being similar to the similarity degree, wherein at least one of the plurality of plaintexts is 0 when the similarity degree is not more than a threshold value;
a plaintext randomization unit to randomize the plurality of plaintexts of the plurality of similar ciphertexts, and generate an assembly of random ciphertexts wherein the plurality of plaintexts randomized are respectively encrypted using the homomorphic encryption; and
a result transmission unit to generate, by using the assembly of the random ciphertexts generated by the plaintext randomization unit, an encryption search result to represent whether or not the similarity degree is not more than the threshold value, and to transmit the encryption search result generated.
[Claim 10] A secret search method of a secret search system including a
management device to store storage data encrypted using a homomorphic encryption as storage encryption data, and a search device to search for the storage data by using search data, the secret search method comprising:
by an encryption similarity calculation unit of the management device, calculating, by performing a homomorphic operation on the storage encryption data, and search encryption data which is the search data being encrypted using the homomorphic encryption, an encryption similarity which is a similarity degree between the storage data and the search data being encrypted using the homomorphic encryption,
by an encryption result transmission unit of the management device, generating

an encryption search result to represent whether or not the similarity degree is not more than a threshold value by using the encryption similarity, and transmitting the encryption search result generated;
by a decryption unit of the search device, decrypting the encryption search result transmitted from the management device, and outputting the encryption search result decrypted as a search result; and
by an output unit of the search device, outputting search result information to represent whether or not the similarity degree is not more than the threshold value, based on the search result.
[Claim 11] A secret search program of a management device to store storage data
encrypted using a homomorphic encryption as storage encryption data, to make a computer execute:
encryption similarity calculation processing to calculate, by performing a homomorphic operation on the storage encryption data, and search encryption data being search data encrypted using the homomorphic encryption, the search data being used in search of the storage data, an encryption similarity which is a similarity degree between the storage data and the search data being encrypted using the homomorphic encryption;
similar ciphertext generation processing to generate a plurality of similar ciphertexts, which are a plurality of plaintexts being respectively encrypted using the homomorphic encryption, the plurality of plaintexts being similar to the similarity degree, wherein at least one of the plurality of plaintexts is 0 when the similarity degree is not more than the threshold value;
plaintext randomization processing to randomize the plurality of plaintexts of

the plurality of similar ciphertexts, and generate an assembly of random ciphertexts, wherein the plurality of plaintexts randomized are respectively encrypted using the homomorphic encryption; and
result transmission processing to generate, by using the assembly of the random ciphertexts generated by the plaintext randomization processing, an encryption search result to represent whether or not the similarity degree is not more than the threshold value, and to transmit the encryption search result generated.