Methods and apparatuses for key generation, encryption and decryption in broadcast encryption

1. A method of key generation performed by an apparatus based on a hierarchical identity based encryption scheme, comprising:

generating, by a processor of the apparatus, a public parameter and a primary key through an initializing method of the encryption scheme, wherein the primary key is based on a first random number;

with respect to each of leaf nodes in a binary tree where subscriber identities are represented by the leaf nodes in the same level, calculating a right key set of a leaf node according to the encryption scheme based on the public parameter, the identity of the leaf node and a right primary key obtained by replacing the first random number with a second random number, the right key set including a right key of the leaf node and right keys of right brother nodes for all the nodes on a path from a root node to the leaf node; and

with respect to the leaf nodes, calculating a left key set of the leaf node according to the encryption scheme based on the public parameter, the identity of the leaf node and a left primary key obtained by replacing the first random number with a third random number, the left key set including a left key of the leaf node and left keys of left brother nodes for all the nodes on the path from the root node to the leaf node,

wherein the sum of the second random number and the third random number equals to the first random number, and the second random number is different for different subscribers.

2. The method according to claim 1 , wherein the encryption scheme is a binary tree encryption scheme of a maximum depth d=┌log 2 n┐ and the public parameter includes a function randomly selected from a 4d−1-wise independent family of functions, where n is a number of subscribers.

3. The method according to claim 1 , wherein the encryption scheme is a Boneh-Boyen-Goh encryption scheme of a maximum depth d=┌log 2 n┐, where n is a number of subscribers.

4. The method according to claim 3 , wherein the public parameter comprises a first g 3 parameter and a second g 3 parameter different from each other, wherein the first g 3 parameter is used for generating the right key set, and the second g 3 parameter is used for generating the left key set.

5. A method of encryption performed by an apparatus based on a hierarchical identity based encryption scheme, comprising:

dividing, by a processor of the apparatus, the identities of subscribers entitled to decrypt a broadcast content into at least one interval;

with respect to each of the interval, encrypting the broadcast content through the encrypting method of the encryption scheme based on a public parameter of the encryption scheme, the lower limit of the interval and a random number associated with the interval, to generate a cipher text and header information associated with the lower limit; and

with respect to each of the interval, encrypting the broadcast content through the encrypting method of the encryption scheme based on the public parameter of the encryption scheme, the upper limit of the interval and the random number associated with the interval, to generate a cipher text and header information associated with the upper limit,

wherein a symmetrical key adopted by the encrypting method of the encryption scheme is based on the random number associated with the interval, and the random number associated with the respective interval is different from each other.

6. The method according to claim 5 , wherein the encryption scheme is a binary tree encryption scheme of a maximum depth d=┌log 2 n┐, and the public parameter includes a function randomly selected from a 4d−1-wise independent family of functions, where n is a number subscribers.

7. The method according to claim 5 , wherein the encryption scheme is a Boneh-Boyen-Goh encryption scheme of a maximum depth d=┌log 2 n┐, where n is a number of subscribers.

8. The method according to claim 7 , wherein the public parameter comprises a first g 3 parameter and a second g 3 parameter different from each other, wherein the first g 3 parameter is used for encryption based on the lower limit, and the second g 3 parameter is used for encryption based on the upper limit.

9. A method performed by an apparatus of decryption based on a hierarchical identity based decrypt scheme, comprising:

receiving information about intervals into which the identities of subscribers entitled to decrypt a broadcast content are divided, a cipher text and header information associated with lower limit of each of the intervals, and a cipher text and header information associated with upper limit of each of the intervals;

finding, by a processor of the apparatus, one of the intervals where the identity of receiving subscriber resides, such that in a binary tree where subscriber identities are represented by leaf nodes in the same level, a left key of one node on a path from a root node to a lower limit node of the interval is included in the left key set of the receiving node corresponding to the identity of the receiving subscriber, and a right key of one node on a path from the root node to the upper limit node of the interval is included in the right key set of the receiving node;

calculating the left key of the lower limit node through the key deriving method of the encryption scheme based on a public parameter, the identity of the node whose left key is included in the left key set and the left key of the node;

calculating the right key of the upper limit node through the key deriving method of the encryption scheme based on the public parameter, the identity of the node whose right key is included in the right key set and the right key of the node;

obtaining a first session key through the decrypting method of the encryption scheme based on the header information associated with the lower limit of the found interval, the left key of a respective lower limit node, the lower limit and the public parameter;

obtaining a second session key through the decrypting method of the encryption scheme based on the header information associated with the upper limit of the found interval, the right key of a respective upper limit node, the upper limit and the public parameter;

obtaining a symmetrical key based on the first session key and the second session key; and

decrypting the cipher text associated with the found interval with the symmetrical key.

10. The method according to claim 9 , wherein the encryption scheme is a binary tree encryption scheme of a maximum depth d=┌log 2 n┐, and the public parameter includes a function randomly selected from a 4d−1-wise independent family of functions, where n is a number of subscribers.

11. The method according to claim 9 , wherein the encryption scheme is a Boneh-Boyen-Goh encryption scheme of a maximum depth d=┌log 2 n┐, where n is a number of subscribers.

12. The method according to claim 11 , wherein the public parameter comprises a first g 3 parameter and a second g 3 parameter different from each other, wherein the first g 3 parameter is used for generating the right key set and encryption based on the lower limit, and the second g 3 parameter is used for generating the left key set and encryption based on the upper limit.

13. An apparatus for key generation based on a hierarchical identity based encryption scheme, comprising:

an initialization device which generates a public parameter and a primary key through an initializing method of the encryption scheme, wherein the primary key is based on a first random number;

a right key set generating device which, with respect to each of leaf nodes in a binary tree where subscriber identities are represented by the leaf nodes in the same level, calculates a right key set of a leaf node according to the encryption scheme based on the public parameter, the identity of the leaf node and a right primary key obtained by replacing the first random number with a second random number, the right key set including a right key of the leaf node and right keys of right brother nodes for all the nodes on a path from a root node to the leaf node; and

a left key set generating device which, with respect to the leaf nodes, calculates a left key set of the leaf node according to the encryption scheme based on the public parameter, the identity of the leaf node and a left primary key obtained by replacing the first random number with a third random number, the left key set including a left key of the leaf node and left keys of left brother nodes for all the nodes on the path from the root node to the leaf node,

wherein the sum of the second random number and the third random number equals to the first random number, and the second random number is different for different subscribers.

14. The apparatus according to claim 13 , wherein the encryption scheme is a binary tree encryption scheme of a maximum depth d=┌log 2 n┐, and the public parameter includes a function randomly selected from a 4d−1-wise independent family of functions, where n is a number of subscribers.

15. The apparatus according to claim 13 , wherein the encryption scheme is a Boneh-Boyen-Goh encryption scheme of a maximum depth d=┌log 2 n┐, where n is a number of subscribers.

16. The apparatus according to claim 15 , wherein the public parameter comprises a first g 3 parameter and a second g 3 parameter different from each other, wherein the first g 3 parameter is used for generating the right key set, and the second g 3 parameter is used for generating the left key set.

17. An apparatus for encryption based on a hierarchical identity based encryption scheme, comprising:

a subscriber grouping device which divides the identities of subscribers entitled to decrypt a broadcast content into at least one interval;

a first encrypting device which, with respect to each of the interval, encrypts the broadcast content through the encrypting method of the encryption scheme based on a public parameter of the encryption scheme, the lower limit of the interval and a random number associated with the interval, to generate a cipher text and header information associated with the lower limit; and

a second encrypting device which, with respect to each of the interval, encrypts the broadcast content through the encrypting method of the encryption scheme based on the public parameter of the encryption scheme, the upper limit of the interval and the random number associated with the interval, to generate a cipher text and header information associated with the upper limit;

wherein a symmetrical key adopted by the encrypting method of the encryption scheme is based on the random number associated with the interval, and the random number associated with the respective interval is different from each other.

18. The apparatus according to claim 17 , wherein the encryption scheme is a binary tree encryption scheme of a maximum depth d=┌log 2 n┐, and the public parameter includes a function randomly selected from 4d−1-wise independent family of functions, where n is a number of subscribers.

19. The apparatus according to claim 17 , wherein the encryption scheme is a Boneh-Boyen-Goh encryption scheme of a maximum depth d=┌log 2 n┐, where n is a number of subscribers.

20. The apparatus according to claim 19 , wherein the public parameter comprises a first g 3 parameter and a second g 3 parameter different from each other, wherein the first g 3 parameter is used for encryption based on the lower limit, and the second g 3 parameter is used for encryption based on the upper limit.

21. An apparatus for decryption based on a hierarchical identity based encryption scheme, comprising:

a receiving device which receives information about intervals into which the identities of subscribers entitled to decrypt a broadcast content are divided, a cipher text and header information associated with lower limit of each of the intervals, and a cipher text and header information associated with upper limit of each of the intervals;

a searching device which finds one of the intervals where the identity of a receiving subscriber resides, such that in a binary tree where subscriber identities are represented by leaf nodes in the same level, a left key of one node on a path from a root node to a lower limit node of the interval is included in the left key set of the receiving node corresponding to the identity of the receiving subscriber, and a right key of one node on a path from the root node to the upper limit node of the interval is included in the right key set of the receiving node;

a key deriving device which calculates the left key of the lower limit node through the key deriving method of the encryption scheme based on a public parameter, the identity of the node whose left key is included in the left key set and the left key of the node, and calculates the right key of the upper limit node through the key deriving method of the encryption scheme based on the public parameter, the identity of the node whose right key is included in the right key set and the right key of the node; and

a key recovering device which obtains a first session key through the decrypting method of the encryption scheme based on the header information associated with the lower limit of the found interval, the left key of a respective lower limit node, the lower limit and the public parameter, obtains a second session key through the decrypting method of the encryption scheme based on the header information associated with the upper limit of the found interval, the right key of a respective upper limit node, the upper limit and the public parameter, and obtains a symmetrical key based on the first session key and the second session key; and

a decrypting device which decrypts the cipher text associated with the found interval with the symmetrical key.

22. The apparatus according to claim 21 , wherein the encryption scheme is a binary tree encryption scheme of a maximum depth d=┌log 2 n┐, and the public parameter includes a function randomly selected from 4d−1-wise independent family of functions, where n is a number of subscribers.

23. The apparatus according to claim 21 , wherein the encryption scheme is a Boneh-Boyen-Goh encryption scheme of a maximum depth d=┌log 2 n┐, where n is a number of subscribers.

24. The apparatus according to claim 23 , wherein the public parameter comprises a first g 3 parameter and a second g 3 parameter different from each other, wherein the first g 3 parameter is used for generating the right key set and encryption based on the lower limit, and the second g 3 parameter is used for generating the left key set and encryption based on the upper limit.