Reception terminal, key management apparatus, and key updating method for public key cryptosystem

• US 20020164035A1
• Filed: 04/11/2002
• Published: 11/07/2002
• Est. Priority Date: 04/12/2001
• Status: Active Grant

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Tatebayashi, Makoto, Yokota, Kaoru
• Granted Patent: US 7,206,412 B2
• Time in Patent Office: Days
• US Class Current: 380/278
• CPC Class Codes: H04L 2209/60 Digital content management, e.g. content distribution
• CPC Class Codes: H04L 9/0822 using key encryption key
• CPC Class Codes: H04L 9/0825 using asymmetric-key encryption or public key infrastructure [PKI], e.g. key signature or public key certificates
• CPC Class Codes: H04L 9/083 involving central third party, e.g. key distribution center [KDC] or trusted third party [TTP]
• CPC Class Codes: H04L 9/0891 Revocation or update of secret information, e.g. encryption key update or rekeying

Abstract

A method for use in a distribution system having a key management center, a distribution station and a reception terminal. The method updates a pair of distribution keys unique to the reception terminal, the distribution public key being used to encrypt distribution data, and the distribution secret key to decrypt encrypted data. In the key updating method, the reception terminal acquires an update secret key prior to data distribution, the key management center acquires an update public key making a pair with update secret key, generates a new pair of distribution keys, encrypts new distribution secret key using update public key, transmits encrypted secret key to the reception terminal and updates to the new distribution public key. The reception terminal receives encrypted secret key and restores new distribution secret key by decrypting it using the update secret key and updates to the new distribution secret key.

Claims

1. A method, for use in a data distribution system having a key management center, a distribution station, and a reception terminal, for updating a pair of a distribution public key and a distribution secret key which conform to a public key cryptosystem and are both unique to the reception terminal, the distribution public key being used to encrypt data to be distributed to the reception terminal, the distribution secret key being used to decrypt the distributed encrypted data, the method comprising:

an update secret key acquiring step in which the reception terminal acquires an update secret key prior to a data distribution;

an update public key acquiring step in which the key management center acquires an update public key that makes a pair with the update secret key, prior to the data distribution;

a key generating step in which the key management center generates a new pair of a distribution public key and a distribution secret key for the reception terminal;

an encrypting step in which the key management center generates an encrypted secret key by encrypting the new distribution secret key using the update public key;

a transmission step in which the key management center transmits the encrypted secret key to the reception terminal;

a distribution public key updating step in which, after the transmission step, the key management center updates the distribution public key having been used so far by the distribution station in data distributions to the new distribution public key;

a reception step in which the reception terminal receives the encrypted secret key; and

a distribution secret key updating step in which the reception terminal restores the new distribution secret key as necessary by decrypting the encrypted secret key using the update secret key, and updates the distribution secret key having been used so far to the restored new distribution secret key.

2. The key updating method of claim 1, wherein

in the encrypting step, the key management center further places a digital signature on the encrypted secret key as a certification of the encrypted secret key, and.

in the distribution secret key updating step, the reception terminal checks the digital signature placed on the encrypted secret key and judges whether the encrypted secret key has the certification, and updates to the new distribution secret key if having judged positively and does not update if having judged negatively.

3. The key updating method of claim 1, wherein

the data distribution system has a plurality of reception terminals,

a plurality of pairs of a distribution public key and a distribution secret key are prepared for the plurality of reception terminals, respectively and uniquely,

each distribution public key is used to encrypt data to be distributed to a corresponding reception terminal,

each distribution secret key is used by a corresponding reception terminal to decrypt distributed encrypted data,

in the update secret key acquiring step, each reception terminal acquires a corresponding update secret key,

in the update public key acquiring step, the key management center acquires a plurality of update public keys that make pairs with the plurality of update secret keys, respectively,

in the key generating step, the key management center generates a plurality of new pairs of a distribution public key and a distribution secret key, each new pair being unique to a different one of the plurality of reception terminals,

in the encrypting step, the key management center generates encrypted secret keys for the plurality of reception terminals by encrypting the new distribution secret keys using the update public keys for the plurality of reception terminals, respectively,

in the transmission step, the key management center transmits the encrypted secret keys to the corresponding reception terminals all at once,

in the distribution public key updating step, after the transmission step, the key management center updates the distribution public keys for the plurality of reception terminals having been used so far by the distribution station in data distributions to the new distribution public keys;

in the reception step, each reception terminal receives a corresponding encrypted secret key, and

in the distribution secret key updating step, each reception terminal restores the corresponding new distribution secret key as necessary by decrypting the corresponding encrypted secret key using the corresponding update secret key, and updates the distribution secret key having been used so far to the restored new distribution secret key.

4. The key updating method of claim 3 further comprising:

a terminal detecting step in which the distribution station detects a reception terminal for which data distribution should be stopped; and

a distribution preventing step in which, when a reception terminal for which data distribution should be stopped is detected in the terminal detecting step, the distribution station prevents data distribution to the detected reception terminal.

5. The key updating method of claim 3 further comprising

a terminal detecting step in which the distribution station detects a reception terminal for which a distribution secret key should be updated, wherein

in the key generating step, the key management center generates a new pair of a distribution public key and a distribution secret key for the reception terminal detected in the terminal detecting step,

in the encrypting step, the key management center generates an encrypted secret key for the detected reception terminal by encrypting the new distribution secret key generated for the detected reception terminal, using the update public key unique to the detected reception terminal,

in the transmission step, the key management center transmits the encrypted secret key for the detected reception terminal to the detected reception terminal,

in the distribution public key updating step, after the transmission step, the key management center updates the distribution public key having been used so far by the distribution station in data distributions to the detected reception terminal, to the new distribution public key, and

in the distribution secret key updating step, the detected reception terminal restores the new distribution secret key as. necessary by decrypting the encrypted secret key using the update secret key, and updates the distribution secret key having been used so far to the restored new distribution secret key.

6. The key updating method of claim 3, wherein

the distribution station generates encrypted contents keys respectively corresponding to the plurality of reception terminals by encrypting a contents key conforming to a secret key cryptosystem using the distribution public keys respectively corresponding to the plurality of reception terminals, generates encrypted contents respectively corresponding to the plurality of reception terminals by encrypting a content using the corresponding contents keys, and distributes (a) all the generated encrypted contents keys and (b) a corresponding encrypted content to each of the plurality of reception terminals, wherein

each reception terminal restores each contents key by decrypting each encrypted contents key among the distributed encrypted contents keys using each distribution secret key for each reception terminal, and restores the content by decrypting each corresponding encrypted content using each restored contents key.

7. The key updating method of claim 1, wherein

the reception terminal has an IC card on which an encrypted secret key unique to the reception terminal is recorded, and the reception terminal restores a distribution secret key by decrypting the encrypted secret key recorded on the IC card, and decrypts distributed encrypted data using the restored distribution secret key,

in the transmission step, the key management center records the encrypted secret key generated in the encrypting step onto a new IC card, and transmits the new IC card to the reception terminal,

in the reception step, the reception terminal receives the new IC card, and

in the distribution secret key updating step, the reception terminal updates to the new distribution secret key by replacing the IC card having been used so far with the new IC card.

8. A reception terminal for restoring certain data by decrypting encrypted certain data distributed from a distribution station, using a distribution secret key unique to the reception terminal, the reception terminal comprising:

an update secret key acquiring means for acquiring an update secret key prior to a data distribution;

a holding means for holding an encrypted secret key which is generated by encrypting the distribution secret key using an update public key that makes a pair with the update secret key;

a reception means for receiving the encrypted data from the distribution station;

a distribution secret key restoring means for restoring the distribution secret key unique to the reception terminal by decrypting the encrypted secret key held by the holding means, using the update secret key acquired by the update secret key acquiring means; and

a data restoring means for restoring the certain data by decrypting the encrypted certain data using the restored distribution secret key.

9. The reception terminal of claim 8 further comprising:

a new key receiving means for receiving a new encrypted secret key from the key management center, the new encrypted secret key being generated by the key management center by encrypting a distribution secret key using the update public key, the distribution secret key making a pair with a distribution public key, the pair being generated by the key management center and conforming to a public key cryptosystem; and

a secret key updating means for updating the encrypted secret key held by the holding means to the new encrypted secret key.

10. The reception terminal of claim 9, wherein

the new encrypted secret key received by the new key receiving means has a digital signature as a certification of the new encrypted secret key, and

after the secret key updating means updates to the new encrypted secret key, the distribution secret key restoring means checks the digital signature placed on the new encrypted secret key and judges whether the new encrypted secret key has the certification, and restores another distribution secret key by decrypting the new encrypted secret key if having judged positively and does not restore another distribution secret key if having judged negatively.

11. The reception terminal of claim 9, wherein

the reception means receives (a) an encrypted contents key generated by encrypting a contents key using the distribution public key unique to the reception terminal and (b) an encrypted content generated by encrypting a content using the contents key, the data restoring means restores the contents key by decrypting the encrypted contents key using the distribution secret key unique to the reception terminal, and restores the content by decrypting the encrypted content using the restored contents key.

12. The reception terminal of claim 9, wherein

the holding means is an IC card,

the new key receiving means receives a new IC card on which the new encrypted secret key is recorded, and

the secret key updating means updates to the new encrypted secret key by replacing the IC card having been used so far with the new IC card.

14. The key management apparatus of claim 13, wherein

the encrypting means further places a digital signature on the encrypted secret key as a certification of the encrypted secret key.

15. The key management apparatus of claim 13, wherein

the update public key acquiring means acquires a plurality of update public keys that are respectively unique to a plurality of reception terminals,

the key generating means generates a plurality of pairs of a distribution public key and a distribution secret key, each pair being unique to a different one of the plurality of reception terminals,

the encrypting means generates encrypted secret keys for the plurality of reception terminals by encrypting the distribution secret keys using the update public keys for the plurality of reception terminals, respectively,

the transmission means transmits the encrypted secret keys to the corresponding reception terminals all at once, and

the distribution public key updating means, after the transmission of the encrypted secret keys, updates the distribution public keys having been used so far to the new distribution public keys for the respective reception terminals.

16. The key management apparatus of claim 15 further comprising:

a terminal detecting means for detecting a reception terminal for which data distribution should be stopped; and

a distribution preventing means for, when a reception terminal for which a data distribution should be stopped is detected by the terminal detecting means, preventing the data distribution to the detected reception terminal.

17. The key management apparatus of claim 15 further comprising:

a terminal detecting means for detecting a reception terminal for which a distribution secret key should be updated, wherein

the key generating means generates a new pair of a distribution public key and a distribution secret key for the reception terminal detected by the terminal detecting means,

the encrypting means generates an encrypted secret key for the detected reception terminal by encrypting the new distribution secret key generated for the detected reception terminal, using the update public key unique to the detected reception terminal,

the transmission means transmits the encrypted secret key for the detected reception terminal to the detected reception terminal,

the distribution public key updating means, after the transmission of the encrypted secret key, updates the distribution public key having been used so far to the new distribution public key, for the detected reception terminal.

18. The key management apparatus of claim 15, wherein

the key management apparatus also serves as a distribution station and further comprises:

a distribution data generating means for generating a plurality of pieces of encrypted data respectively for the plurality of reception terminals by encrypting certain data using distribution public keys for the plurality of reception terminals; and

a distribution means for distributing all the plurality of pieces of encrypted data to each of the plurality of reception terminals.

19. The key management apparatus of claim 18, wherein

the distribution data generating means generates a plurality of pieces of encrypted contents keys respectively for the plurality of reception terminals by encrypting a contents key using the distribution public keys for the plurality of reception terminals, and generates encrypted contents respectively corresponding to the plurality of reception terminals by encrypting a content using the corresponding contents keys, and

the distribution means distributes (a) all the generated encrypted contents keys and (b) a corresponding encrypted content to each of the plurality of reception terminals.

20. The key management apparatus of claim 13, wherein

the reception terminal has an IC card on which an encrypted secret key unique to the reception terminal is recorded, and the reception terminal restores a distribution secret key by decrypting the encrypted secret key recorded on the IC card, and decrypts distributed encrypted data using the restored distribution secret key,

the transmission means records the encrypted secret key generated by the encrypting means onto a new IC card, and transmits the new IC card to the reception terminal.

13. A key management apparatus, comprising:

an update public key acquiring means for acquiring, prior to a data distribution, an update public key that makes a pair with an update secret key held by a reception terminal;

a key generating means for generating a pair of a distribution public key and a distribution secret key for the reception terminal;

an encrypting means for generating an encrypted secret key by encrypting the distribution secret key using the update public key;

a transmission means for transmitting the encrypted secret key to the reception terminal;

a distribution public key updating means for, after the transmission step, updating the distribution public key having been used so far to the new distribution public key for use in data distribution.