Encryption system for distributing a common crypt key

Details Encryption system for distributing a common crypt key Encryption system for distributing a common crypt key

1998-10-30

2003-04-15

Smithers, Matthew (Department: 2134)

Electrical computers and digital processing systems: support

Multiple computer communication using cryptography

Particular communication authentication technique

C380S229000

Reexamination Certificate

active

06550009

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an encryption system for decoding encrypted data recorded in a portable storage medium, and in particular to an encryption system for distributing a common crypt key using encryption information in BCA (burst cutting area) of a DVD-ROM.
2. Description of the Prior Art
In order to protect data in CD-ROM or DVD-ROM from being copied illegally, data are generally encrypted. There will be no meaning in the encryption unless a common crypt key for restoring the encrypted data is safely distributed, and it is necessary to have a method to safely distribute a common crypt key. One of the methods for safe distribution of the common crypt key is a method to use a public key encryption.
FIG. 3
is a block diagram of a DVD-ROM encryption system designed according to conventional common technique in order to acquire a common crypt key using a public key encryption method.
Description will be given now on the method to acquire a common crypt key by the public key encryption method referring to FIG.
3
. Here, it is assumed that a user A receives a common crypt key from a server B on on-line basis. It is also assumed that the data encrypted by the common crypt key is at hand (on DVD-ROM) of the user A and that the user A can specify the index information which can designate a common crypt key required. In acquiring the common crypt key, it is generally necessary to take the following procedure:
(1) A request to acquire a common crypt key is given from the user A to the server B.
(1-1) An index information to specify a common crypt key of what is to be acquired is obtained.
(1-2) An information for the request is prepared by random information such as the current time.
(1-3) A hash value is calculated from the information for request using hash function.
(1-4) Secret key of the user A is read from an IC card
15
.
(1-4-1) To the IC card
15
storing the secret key, the user A is requested to enter a password.
(1-4-2) An IC card reader checks whether the password is correct or not and reads the stored secret key.
(1-5) Using the secret key of the user A, signature is calculated from the hash value.
(1-6) A public key certificate of the user A is obtained from a storage device (hard disk) of a personal computer.
(1-7) A public key of the server B is obtained from a certificate issuing center
4
.
(1-8) To the information and the signature for request, RSA encryption is performed using the public key of the server B, and it is sent to the server B together with the public key certificate of the user A.
(2) The server B authenticates the request from the user A.
(2-1) To the public key certificate of the user A, correctness is confirmed using the public key of the certificate issuing center
4
, and the public key of the user A is obtained.
(2-2) The secret key of the server B is read from an IC card
25
. (The same procedure as in (1-4)).
(2-3) The information and the signature for the request are restored using the secret key of the server B.
(2-4) Hash value X is calculated from the information for request using hash function.
(2-5) Hash value Y is restored using the public key of the user A from the signature of the user A.
(2-6) It is checked whether the hash value X obtained in the step (2-4) is the same as the hash value Y obtained in the step (2-5). If it is the same, it is confirmed that it is a request information from the user A.
(3) The server B delivers a common crypt key to the user A.
(3-1) The server B specifies a common crypt key necessary from a key DB
22
using request information.
(3-2) An information for response is prepared by adding random information such as the current time.
(3-3) Hash value is calculated from the information for response using hash function.
(3-4) The secret key of the server B is read from the IC card
25
. (The same procedure as in (1-4))
(3-5) Using the secret key of the server B, signature is calculated from the hash value.
(3-6) A public key certificate of the server B is obtained from a storage device (hard disk)
26
of a personal computer.
(3-7) To the information and the signature for response, RSA encryption is performed using the public key of the user A, and it is transmitted to the user A together with the public key certificate of the server B.
(4) The user A authenticates the response from the server B, obtains the common crypt key, and restores the data.
(4-1) To the public key certificate of the server B, correctness is confirmed using the public key at the certificate issuing center
4
, and the public key of the server B is obtained.
(4-2) The secret key of the user A is read from the IC card
15
. (The same procedure as in (1-4))
(4-3) Using the secret key of the user A, the information and the signature for response are restored.
(4-4) Hash value U is calculated from the information for the response using hash function.
(4-5) Hash value V is restored using the public key of the server B from the signature of the server B.
(4-6) It is checked whether the hash value U obtained in the step (4-4) is the same as the hash value V obtained in the step (4-5). If it is the same, it is confirmed that it is response information from the server B.
(4-7) From the information for response, the common crypt key is separated, and a common crypt key is obtained.
(4-8) From encryption data in DVD-ROM
12
, the data is restored by the common crypt key.
As far as each secret key is protected by the above method, it is almost perfectly possible to defend against wire tapping on communication route or against attacker who pretends to be or disguises as the other user. When the common crypt key has been obtained and if it is stored as it is encrypted by the public key of the user A without directly storing it in hard disk of the personal computer, it is also possible to defend against attack at the time of storage.
In the above procedure, however, it is necessary to check the correctness of the public keys with each other using the public key of the certificate issuing center. Because there is only one secret key respectively, it is necessary to store the key in IC card and the like as described above to ensure safety and to control by password. For this purpose, it is necessary to have a special device (such as IC card reader). This often leads to the problems such as complicated procedure or large-scale design of the system.
Further, safety against attack such as wire tapping of data or disguise or falsification of data depends upon the safety of the control of the secret key of each individual. In this respect, even when the system itself is robust and durable, the safety of the entire system depends upon the managing and controlling ability of each individual. In this sense, the more the users are increased, the bigger the problem may become in actual operation of the system.
To solve the above problems, it is an object of the present invention to safely distribute a common crypt key such as DVD-ROM by simplified devices and procedure.
SUMMARY OF THE INVENTION
To solve the above problems, in the encryption system according to the present invention, an encrypted data decryption device comprises means for sending a data request to a data encryption device, and means for decrypting the data received from the data encryption device using a medium specific information, and the data encryption device comprises means for obtaining the medium specific information corresponding to data request by searching a medium specific information data base, and means for encrypting and transmitting transmission data using the medium specific information. With such an arrangement, it is possible to encrypt and transmit the data using the medium specific information already distributed as a crypt key by simple devices and procedure.
Also, in a terminal equipment such as a DVD-ROM system, there is provided means for decrypting the received data using BCA data, and the center device comprises means for obtaining BCA data of a user by searching BCA data base, and means for encrypting and

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