Abstract: According to an embodiment of the present invention, an issue system previously issues a smart card, and sends an encrypted private key and a public key certificate to a user terminal, when issuing a new card or updating an old card. A user terminal inputs the received encrypted private key and public key certificate into a smart card. A smart card stores a public key certificate, and decrypts the inputted encrypted private key by an encryptor/decryptor based on a symmetric key, and stores the obtained private key. Therefore, collection and redistribution of a smart card becomes unnecessary, when updating a private key and a public key certificate, saving the time and labor.

Abstract: An apparatus for adding an electronic signature to document data includes a delimiter character detector for dividing the input document data into a plurality of divided document data by using as a delimiter a predetermined character appearing in a document represented by the document data, a digest generator and an encrypter for generating an electronic signature based on the divided document data for each divided document data, and a signature-added message generator for generating the divided document data, the electronic signature based on the divided document data, and information for associating the divided document data with the electronic signature.

Abstract: A digital signal decoding apparatus includes an equalizing section for equalizing a digital signal and outputting a digital signal having effective values at a plurality of sensing points. An extracting section extracts a plurality of amplitude information with narrower timing than the time interval of the digital signal outputted from the equalizing section. A decoding section decodes the digital signal from the plurality of amplitude information extracted by the extracting section. A control section performs a predetermined operation on the plurality of amplitude information extracted by the extracting section and on the basis of the operation result, controlling the level of a reference value used in decoding by the decoding section.

Abstract: A digital signal decoding apparatus includes a maximum-likelihood decoding portion in which a digital signal consisting of compression block data obtained by compressing every plurality of digital data units is subjected to maximum-likelihood decoding, thereby to output a maximum-likelihood decoded digital signal. A detection portion receives a maximum-likelihood decoded digital signal from the maximum-likelihood decoding means and detects at least one compression block data unit, thereby to output a predetermined control signal. An initialization portion initializes maximum-likelihood information used for the maximum-likelihood decoding by the maximum-likelihood decoding means, to a predetermined value on the basis of the control signal outputted from the detection portion.

Abstract: A rotary head device for a recording and reproducing apparatus includes a rotary drum and a stationary drum. The rotary drum has a guide surface formed of a conical surface coaxial with the axis of rotation of the rotary drum and wound with a magnetic tape. A head unit is mounted on the rotary drum to be rotatable integrally therewith. The head unit includes two head elements facing each other, for scanning the tape wound on the guide surface, while the tape is being interposed between the head elements, as the rotary drum rotates.