secret search system comprising: a transmission device generating encrypted data and an encryption tag which is an encrypted keyword for searching the encrypted data; a server device receiving from the transmission device and storing the encrypted data and the encryption tag, and also conducting a secret search in response to a request for the secret search; and a reception device generating a trapdoor which is data corresponding to a digital signature of the keyword and also data requesting the server device to conduct the secret search of the encrypted data, sending the trapdoor to the server device, and receiving a result of the secret search from the server device, and a key generation device comprising: a first generation unit which generates a true public parameter PP included in a public parameter PK, the public parameter PK being the key information including: the true public parameter PP used for encryption of the keyword by the transmission device, generation of the trapdoor by the reception device, and the secret search by the server device; and a protection key PK' used for the encryption of the keyword by the transmission device and the generation of the trapdoor by the reception device; and a second generation unit which generates the protection key PK' included in the public parameter PK separately from the true public parameter PP generated by the first generation unit. a transmission device generating encrypted data and an encryption tag which is an encrypted keyword for searching the encrypted data; a server device receiving from the transmission device and storing the encrypted data and the encryption tag, and also conducting a secret search in response to a request for the secret search; and a reception device generating a trapdoor which is data corresponding to a digital signature of the keyword and also data requesting the server device to conduct the secret search of the encrypted data, sending the trapdoor to the server device, and receiving a result of the secret search from the server device, and a key generation device comprising: a first generation unit which generates a true public parameter PP included in a public parameter PK, the public parameter PK being the key information including: the true public parameter PP used for encryption of the keyword by the transmission device, generation of the trapdoor by the reception device, and the secret search by the server device; and a protection key PK' used for the encryption of the keyword by the transmission device and the generation of the trapdoor by the reception device; and a second generation unit which generates the protection key PK' included in the public parameter PK separately from the true public parameter PP generated by the first generation unit. a first generation unit which generates a true public parameter PP included in a public parameter PK, the public parameter PK being the key information including: the true public parameter PP used for encryption of the keyword by the transmission device, generation of the trapdoor by the reception device, and the secret search by the server device; and a protection key PK' used for the encryption of the keyword by the transmission device and the generation of the trapdoor by the reception device; and a second generation unit which generates the protection key PK' included in the public parameter PK separately from the true public parameter PP generated by the first generation unit. the true public parameter PP used for encryption of the keyword by the transmission device, generation of the trapdoor by the reception device, and the secret search by the server device; and a protection key PK' used for the encryption of the keyword by the transmission device and the generation of the trapdoor by the reception device; and a second generation unit which generates the protection key PK' included in the public parameter PK separately from the true public parameter PP generated by the first generation unit.