(Amended) A data processing apparatus connected to a data storage apparatus that stores a plurality of encrypted data and tag data being related to each of the plurality of encrypted data and being collated when the plurality of encrypted data are searched, the data processing apparatus comprising: a keyword specification unit (302,306) that specifies a keyword of storage target data being a target to be stored in the data storage apparatus, as a storage keyword; an allowed bit position specification unit that specifies a bit position where disclosure of a bit value to the data storage apparatus is allowed, as an allowed bit position; an index derive bit sequence generation unit that generates a bit sequence from the storage keyword by performing a generation procedure, as a storage index derive bit sequence; and a concealing processing unit (308,310) that performs concealing processing to disclose the bit value at the allowed bit position in the storage index derive bit sequence to the data storage apparatus, and to conceal bit values at other than the allowed bit position in the storage index derive bit sequence from the data storage apparatus, and that causes the data storage apparatus to derive a storage index value, which is to be attached to the tag data by the data storage apparatus when the tag data to be related to encrypted data of the storage target data is stored, from the bit value disclosed at the allowed bit position in the storage index derive bit sequence, wherein the concealing processing unit generates, for the respective allowed bit positions, a decryption key used for decrypting an encrypted bit at the allowed bit position, as an allowed bit decryption key, the data processing apparatus further comprising: an allowed bit decryption key transmission unit that transmits the allowed bit decryption key to the data storage apparatus, wherein the concealing processing unit encrypts the storage index derive bit sequence by an encryption scheme in which the encrypted bit at the allowed bit position is decrypted with the allowed bit decryption key and encrypted bits at other than the allowed bit position are not decrypted with the allowed bit decryption key, the data processing apparatus further comprising: a storage request transmission unit that transmits a storage request including the encrypted data of the storage target data, the tag data to be related to the encrypted data of the storage target data, and an encrypted storage index derive bit sequence to the data storage apparatus. a keyword specification unit (302,306) that specifies a keyword of storage target data being a target to be stored in the data storage apparatus, as a storage keyword; an allowed bit position specification unit that specifies a bit position where disclosure of a bit value to the data storage apparatus is allowed, as an allowed bit position; an index derive bit sequence generation unit that generates a bit sequence from the storage keyword by performing a generation procedure, as a storage index derive bit sequence; and a concealing processing unit (308,310) that performs concealing processing to disclose the bit value at the allowed bit position in the storage index derive bit sequence to the data storage apparatus, and to conceal bit values at other than the allowed bit position in the storage index derive bit sequence from the data storage apparatus, and that causes the data storage apparatus to derive a storage index value, which is to be attached to the tag data by the data storage apparatus when the tag data to be related to encrypted data of the storage target data is stored, from the bit value disclosed at the allowed bit position in the storage index derive bit sequence, wherein the concealing processing unit generates, for the respective allowed bit positions, a decryption key used for decrypting an encrypted bit at the allowed bit position, as an allowed bit decryption key, the data processing apparatus further comprising: an allowed bit decryption key transmission unit that transmits the allowed bit decryption key to the data storage apparatus, wherein the concealing processing unit encrypts the storage index derive bit sequence by an encryption scheme in which the encrypted bit at the allowed bit position is decrypted with the allowed bit decryption key and encrypted bits at other than the allowed bit position are not decrypted with the allowed bit decryption key, the data processing apparatus further comprising: a storage request transmission unit that transmits a storage request including the encrypted data of the storage target data, the tag data to be related to the encrypted data of the storage target data, and an encrypted storage index derive bit sequence to the data storage apparatus. an allowed bit decryption key transmission unit that transmits the allowed bit decryption key to the data storage apparatus, wherein the concealing processing unit encrypts the storage index derive bit sequence by an encryption scheme in which the encrypted bit at the allowed bit position is decrypted with the allowed bit decryption key and encrypted bits at other than the allowed bit position are not decrypted with the allowed bit decryption key, the data processing apparatus further comprising: a storage request transmission unit that transmits a storage request including the encrypted data of the storage target data, the tag data to be related to the encrypted data of the storage target data, and an encrypted storage index derive bit sequence to the data storage apparatus.