Electrical computers and digital processing systems: support – Multiple computer communication using cryptography – Particular communication authentication technique
Reexamination Certificate
1999-02-08
2002-11-26
Smithers, Matthew (Department: 2132)
Electrical computers and digital processing systems: support
Multiple computer communication using cryptography
Particular communication authentication technique
Reexamination Certificate
active
06487659
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique for authenticating whether a user has the authority to receive service in connection with restrictions such as the term of utilization. According to this technique, the authentication fails if information on the restrictions has been altered. The present invention is also concerned with a technique for decrypting encrypted messages. Particularly, it is verified that information pieces annexed to messages such as information on the term of utilization and control information have not been altered, and only when such information pieces have not been altered, the messages are decrypted correctly.
2. Description of the Prior Art
According to a conventional method for authenticating whether a user has the authority to receive service, the authentication side issues a physical ticket or membership card in advance and the user presents the ticket or the membership card when the user is to receive the service. In this case, the service offerer checks, on the spot, the information pieces described on the ticket or the like such as the valid term and the type of service and thereby effects checking and authentication of conditions. However, since the ticket itself is a physical existence, drawbacks have heretofore been encountered such as an increase in cost for the distribution of such tickets to users or an increase in the ticket manufacturing cost because of a requirement for taking a certain measure to make ticket forgery difficult. On this regard, by making the ticket electronically operable, it becomes possible to reduce the cost of manufacture and distribution. Related techniques are disclosed in Japanese Published Unexamined Patent Application No. Sho 62-171071 entitled “IC Card for Advance Transaction” and Japanese Published Examined Patent Application No. Hei 6-22032 entitled “Public Services Payment System using Electronic Card.” In these techniques, however, electronic information corresponding to a ticket is merely nullified upon receipt of service, making no contribution to the implementation of a more versatile ticket such as a coupon type ticket or a combination of a limitation on the term of utilization with a limitation on the amount of utilization. In addition, the above conventional techniques lack in any protective measure against wiretapping of communication between the card and the host at the time of obtaining a ticket electronically or against illegitimate utilization of a ticket made by replay attack.
Further, as a conventional technique involving an additional function of restricting utilization on encrypted digital information, there is known a technique disclosed in Japanese Published Unexamined Patent Application No. Hei 7-131452 which is directed to “Digital Information Protecting Method and Processing Device Therefor.” In the invention disclosed therein, digital information is represented by a set of information identifying number, information itself, utilization conditions information, and authenticator. Further, upon input of digital information into a computer, there is generated a second identifier relating to the information identifying number and the utilization conditions information. Then, in utilizing the digital information, there is made verification using two identifiers as to whether or not the utilization conditions described in the utilization conditions information are satisfied, and only when all of the points to be verified have been verified normally, the digital information is decrypted and converted into a utilizable form. However, according to the method disclosed in the above Hei 7-131452, both information itself and utilization conditions are encrypted using the same encryption key for the assurance of a legitimate combination of the two, so when an attempt is made to change utilization conditions for each user, for example, it is necessary to perform encryption every time communication is made or provide corresponding ciphers beforehand for each communication. Thus, the above method has not been suitable for a large-volume distribution of digital information using CD-ROM or the like or for a broadcast that utilizes a satellite broadcast.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the above-mentioned problems. According to what is intended by the present invention, at the time of authenticating whether or not a user has the authority to utilize service, what is corresponding to the conventional ticket is made electronic, and in determining whether or not the electronic information thus obtained is legitimate, it is possible to set flexible conditions such as the valid term and a limitation on the number of times of utilization, or a combination thereof, while ensuring safety; further, in the event the conditions should have been altered, authentication is not effected affirmatively.
According to another object of the present invention, at the time of conditionally decrypting an encrypted digital information, it is possible to set decryption conditions, etc. for utilization of the digital information in a decrypted state, which decryption conditions, etc. are independent of the encrypted digital information itself, and therefore it is easy to allocate different conditions, etc. for each user; further, in the event decryption conditions have been altered, decryption of the digital information is not performed correctly.
In the present invention, for achieving the above-mentioned object, an authentication device includes a proof data generation device in which data is generated for authenticating the authority of a user and verification device for verifying the legitimacy of the generated proof data; the proof data generation device includes a first memory part that stores authentication data generated by the verification device, a second memory part that stores control information for generating the proof data, a third memory part that stores proof support information calculated from authentication characteristic information and the control information which is for generating the proof data, and a proof data generation part that generates proof data on the basis of the information pieces stored in the above memory parts; the verification device includes a verification part that verifies that the proof data generated by the proof data generating part is based on the authentication characteristic information; and the authentication characteristic information is a decryption key used in an asymmetric cryptosysytem which utilizes a discrete logarithmic problem on a finite group G.
According to this construction, first, at the time of determining the legitimacy of an electronic ticket, it is possible to set flexible conditions such as the valid term and a limitation on the number of times of utilization, or a combination thereof, while ensuring safety. In addition, it is possible to make control so that authentication is not performed affirmatively in the event those conditions have been altered. Secondly, in the case of conditionally decrypting an encrypted digital information, it is possible to set decryption conditions, etc. for utilization of the digital information in a decrypted state. Further, the decryption conditions, etc. are independent of the encrypted digital information itself, so that it is easy to allocate different conditions, etc. for each user, and in the event of alteration of the decryption conditions, etc., it is possible to prevent the digital information from being decrypted correctly.
Moreover, by using as the authentication characteristic information an asymmetric cryptosysytem which is defined on an elliptic curve on a finite field, there is attained equivalent safety even with a shorter key length in comparison with the use of an RSA public key cipher for example, and the processing can be done at a high speed.
The present invention can be implemented as a method or as a computer program product.
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Kigo Kenichiro
Suzuki Kohji
Oliff & Berridg,e PLC
Smithers Matthew
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