System and method for secure group communications via multicast or broadcast

• US 5,748,736 A
• Filed: 06/14/1996
• Issued: 05/05/1998
• Est. Priority Date: 06/14/1996
• Status: Expired due to Term

• Current Assignee: Suvo Mittra
• Original Assignee: Suvo Mittra
• Inventors: Mittra, Suvo
• Primary Examiner(s): Cain, David C.
• Application Number:
  US08/665,195
• Time in Patent Office: 690 Days
• Field of Search: 380/21, 380/48, 380/9, 380/20, 380/49
• US Class Current: 713/163
• CPC Class Codes: H04L 12/18 for broadcast or conference , e.g. multicast
• CPC Class Codes: H04L 12/185 with management of multicast group membership
• CPC Class Codes: H04L 63/0428 wherein the data content is protected, e.g. by encrypting or encapsulating the payload
• CPC Class Codes: H04L 63/065 for group communications cryptographic mechanisms or cryptographic arrangements for key management involving conference or group key H04L9/0833
• CPC Class Codes: H04L 63/104 Grouping of entities
• CPC Class Codes: H04L 63/123 received data contents, e.g. message integrity
• CPC Class Codes: H04L 63/126 the source of the received data
• CPC Class Codes: H04L 9/0822 using key encryption key
• CPC Class Codes: H04L 9/0833 involving conference or group key network architectures or network communication protocols for key management in group communication in a packet data network H04L63/065
• CPC Class Codes: H04L 9/0891 Revocation or update of secret information, e.g. encryption key update or rekeying

Abstract

A system and method for secure group communication via multicast or broadcast transmission. In preferred embodiments, the system of the invention implements a secure multicast group consisting of senders, receivers, a group security controller (GSC), and at least one trusted intermediary (TI) server. The GSC and each TI server are responsible for maintaining the security of the group by authenticating and authorizing all other members of the multicast as well as managing the group key(s) (Kgrp(s)) that are used to encrypt the messages multicast to the group. Any member of the group may have more than one role at a time. For example, senders may also be receivers, and the GSC may be combined with one of the senders. Each TI server is a trusted intermediary, which is a special type of sender and receiver. The TI servers create a (logical) hierarchy of secure multicast networks (a secure distribution tree) that makes the system of the invention scalable (able to practically implement a group of any number of members). Some embodiments of the system implement a security protocol supporting data confidentiality, source authentication, data integrity, and sender non-repudiation. Implementation of the system does not require use of any specific security technology (i.e. cryptographic and authentication tools). The decision to use one technology over another is left to the implementor.

Claims

1. A system for implementing a secure multicast group in a scalable manner, said system including:

a group security controller which encrypts data with a first group key and causes the encrypted data to be multicast to a first sub-group; and

a number of trusted intermediary servers, wherein each of the trusted intermediary servers can encrypt data with a different group key and cause the differently encrypted data to be multicast to a different sub-group, wherein each said different group key is different from the first group key and each said different sub-group is different from the first subgroup, and wherein the group security controller and each of the trusted intermediary servers form a logical hierarchy of sub-groups which determine said secure multicast group, with the first sub-group at a top level of said hierarchy and each of the sub-groups associated with a different one of the group security controller and the trusted intermediary servers.

2. The system of claim 1, wherein the trusted intermediary servers include a first trusted intermediary server associated with a sub-group at a first level of the hierarchy, the first level is lower than at least one other level of the hierarchy, the first trusted intermediary server can decrypt a message that has been multicast from said other level using a group key associated with said other level, and the first trusted intermediary server can reencrypt the message using a group key different from the group key associated with said other level and initiate a multicast of the reencrypted message to the sub-group at said first level.

3. The system of claim 1, wherein each of the trusted intermediary servers acts as a full proxy to exactly one of the group security controller or another of the trusted intermediary servers.

4. The system of claim 1, wherein each member of the secure multicast group communicates over a network having protocols, and the group security controller and the trusted intermediary servers are independent in design of the network and said protocols.

5. The system of claim 1, wherein the group security controller causes the encrypted data to be broadcast to the first sub-group, and said each of the trusted intermediary servers causes the differently encrypted data to be broadcast to said different sub-group.

6. The system of claim 1, wherein the group security controller causes the encrypted data to be multicast other than via broadcast to the first sub-group, and said each of the trusted intermediary servers causes the differently encrypted data to be multicast other than via broadcast to said different sub-group.

7. The system of claim 1, wherein the group security controller causes the encrypted data to be multiply unicast to the first sub-group, and said each of the trusted intermediary servers causes the differently encrypted data to be multiply unicast to said different subgroup.

8. The system of claim 1, wherein the trusted intermediary servers include a first trusted intermediary server associated with a second sub-group and a second group key, said system also including:

a receiver which communicates with the first trusted intermediary server, wherein in response to a request from the receiver for permission to join the secure multicast group, the first trusted intermediary server attempts to authenticate the receiver and check that the receiver has permission to join the secure multicast group, and upon determining that the receiver has said permission, the first trusted intermediary server securely distributes the second group key to the receiver.

9. The system of claim 1, wherein the trusted intermediary servers include a first trusted intermediary server associated with a first sub-group and a second group key, said system also including:

a receiver which communicates with the first trusted intermediary server, wherein in response to a request from the receiver for permission to join the secure multicast group, the first trusted intermediary server attempts to authenticate the receiver and checks that the receiver has permission to join the secure multicast group, and upon determining that the receiver has said permission, the first trusted intermediary server determines a new group key to replace the second group key and securely distributes the new group key to the receiver and all members of the second sub-group that hold the second group key.

10. The system of claim 1, also including:

a receiver which communicates with the group security controller, wherein in response to a request from the receiver for permission to join the secure multicast group, the group security controller attempts to authenticate the receiver and checks that the receiver has permission to join the secure multicast group, and upon determining that the receiver has said permission, the group security controller determines a new group key to replace the first group key and securely distributes the new group key to the receiver and all members of the first sub-group that hold the first group key.

11. The system of claim 1, also including:

a receiver which communicates with the group security controller, wherein in response to a request from the receiver for permission to join the secure multicast group, the group security controller server attempts to authenticate the receiver and check that the receiver has permission to join the secure multicast group, and upon determining that the receiver has said permission, the group security controller server securely distributes the first group key to the receiver.

12. The system of claim 1, wherein the trusted intermediary servers include a first trusted intermediary server associated with a second sub-group and a second group key, said system also including:

a receiver which communicates with the first trusted intermediary server, wherein in response to a request to cause a first member of the second sub-group to leave the secure multicast group, the first trusted intermediary server determines a new group key to replace the second group key and securely distributes the new group key to all members of the second sub-group that hold the second group key other than said first member.

13. The system of claim 1, also including:

a receiver which communicates with the group security controller, wherein in response to a request to cause a first member of the first sub-group to leave the secure multicast group, the group security controller determines a new group key to replace the first group key and securely distributes the new group key to all members of the first sub-group that hold the first group key other than said first member.

14. The system of claim 1, wherein the trusted intermediary servers include a first trusted intermediary server associated with a second sub-group and a second group key, said system also including:

a sender which communicates with the first trusted intermediary server, wherein in response to a request from the sender for permission to join the secure multicast group, the first trusted intermediary server attempts to authenticate the sender and check that the sender has permission to join the secure multicast group, and upon determining that the sender has said permission, the first trusted intermediary server securely distributes the second group key to the sender.

15. The system of claim 1, wherein the trusted intermediary servers include a first trusted intermediary server associated with a second sub-group and a second group key, said system also including:

a sender which communicates with the first trusted intermediary server, wherein in response to a request from the sender for permission to join the secure multicast group, the first trusted intermediary server attempts to authenticate the sender and check that the sender has permission to join the secure multicast group.

16. The system of claim 1, wherein the trusted intermediary servers include a first trusted intermediary server associated with a first sub-group and a second group key, said system also including:

a sender which communicates with the first trusted intermediary server, wherein in response to a request from the sender for permission to join the secure multicast group, the first trusted intermediary server attempts to authenticate the sender and checks that the sender has permission to join the secure multicast group, and upon determining that the sender has said permission, the first trusted intermediary server determines a new group key to replace the second group key and securely distributes the new group key to the sender and all members of the second sub-group that hold the second group key.

17. The system of claim 1, also including:

a sender which communicates with the group security controller, wherein in response to a request from the sender for permission to join the secure multicast group, the group security controller attempts to authenticate the sender and checks that the sender has permission to join the secure multicast group, and upon determining that the sender has said permission, the group security controller determines a new group key to replace the first group key and securely distributes the new group key to the sender and all members of the first sub-group that hold the first group key.

18. The system of claim 1, also including:

a sender which communicates with the group security controller, wherein in response to a request from the sender for permission to join the secure multicast group, the group security controller attempts to authenticate the sender and check that the sender has permission to join the secure multicast group, and upon determining that the sender has said permission, the group security controller securely distributes the first group key to the sender.

19. The system of claim 1, also including:

a sender which communicates with the group security controller, wherein in response to a request from the sender for permission to join the secure multicast group, the group security controller attempts to authenticate the sender and check that the sender has permission to join the secure multicast group.

43. The system of claim 8, wherein each member of the secure multicast group communicates over a network having protocols, and the group security controller and the trusted intermediary servers are independent in design of the network and said protocols.

20. A system for implementing a secure multicast group in a scalable manner, said system including:

a group security controller which encrypts data with a first group key and causes the encrypted data to be multicast to a first sub-group; and

a number of trusted intermediary servers, wherein each of the trusted intermediary servers can encrypt data with a different group key and cause the differently encrypted data to be multicast to a different sub-group, wherein each said different group key can be different from the first group key and each said different sub-group is different from the first sub-group, and wherein the group security controller and each of the trusted intermediary servers form a logical hierarchy of sub-groups which determine said secure multicast group, with the first sub-group at a top level of said hierarchy and each of the sub-groups associated with a different one of the group security controller and the trusted intermediary servers.

21. A system for implementing a secure multicast group in a scalable manner, said system including:

a security controller which controls access to the secure multicast group; and

a sender which communicates with the security controller, and wherein the security controller is programmed with verification software for responding to a message received from the sender by verifying that the sender has permission to send said message to the secure multicast group, wherein upon determining that the sender has said permission, the security controller generates a digital signature and multicasts the message with said digital signature to at least a sub-group of the group.

22. The system of claim 21, wherein the security controller is a group security controller.

23. The system of claim 21, wherein the security controller is a trusted intermediary server.

24. The system of claim 21, also including:

a receiver which receives multicast transmissions from any member of the group, wherein the receiver is programmed with verification software for responding to said message by verifying that the sender has permission to send to the secure multicast group as evidenced by the digital signature.

25. A system for implementing a secure multicast group in a scalable manner, said system including:

a sender;

a security controller which controls access to the secure multicast group and communicates with the sender over a secure channel, wherein the security controller is programmed with software for verifying that the sender has permission to send data to the secure multicast group and upon determining that the sender has said permission, for causing the security controller to generate a digitally signed certificate and send said digitally signed certificate to the sender, wherein upon receiving the digitally signed certificate, the sender multicasts data to at least a sub-group of the group with said digitally signed certificate.

26. The system of claim 25, wherein the security controller is a group security controller.

27. The system of claim 25, wherein the security controller is a trusted intermediary server.

28. The system of claim 25, also including:

a receiver which receives multicast transmissions, wherein the receiver is programmed with verification software for responding to said message by verifying that the sender has permission to send to the secure multicast group as evidenced by inclusion of said digitally signed certificate.

29. A system for implementing a secure multicast group in a scalable manner, said system including:

a group security controller;

a trusted intermediary server which communicates with the group security controller over a multicast network; and

at least a first receiver which communicates with the trusted intermediary server over a second multicast network, wherein the trusted intermediary server is programmed with software for responding to a request from a prospective group member to join the secure multicast group by performing an authorization operation, and upon successful completion of the authorization operation determining a new group key and sending the new group key to the prospective group member and to the first receiver over the second multicast network.

30. The system of claim 29, also including:

a second receiver which communicates with the trusted intermediary server over a second multicast network, wherein the trusted intermediary server is also programmed with software for responding to a request from a prospective group member to leave the secure multicast group by determining a second new group key and sending the second new group key to the first receiver over the second multicast network.

31. The system of claim 29, also including:

a second receiver which communicates with the trusted intermediary server over a second multicast network, wherein the trusted intermediary server is also programmed with software for responding to a request from the group security controller to cause the second receiver to leave the secure multicast group by determining a second new group key and sending the second new group key to the first receiver over the second multicast network.

32. A system for implementing a secure multicast group in a scalable manner, said system including:

a group security controller;

a first trusted intermediary server which communicates with the group security controller over a first multicast network;

a second trusted intermediary server which communicates with the first trusted intermediary server over a second multicast network; and

at least a first receiver which communicates with the second trusted intermediary server over a third multicast network, wherein the second trusted intermediary server is programmed with software for responding to a request from a prospective group member to join the secure multicast group by performing an authorization operation, and upon successful completion of the authorization operation determining a new group key and sending the new group key to the prospective group member over a secure channel and to the first receiver over the third multicast network.

33. The system of claim 32, also including:

a second receiver which communicates with the first trusted intermediary server over the second multicast network, and wherein the second trusted intermediary server communicates with the first receiver over the third multicast network using a first group key, and the first trusted intermediary server communicates with the second receiver over the second multicast network using a second group key.

34. The system of claim 33, also including:

a third receiver which communicates with the group security controller over the first multicast network, and wherein the group security controller communicates with the third receiver over the first multicast network using a third group key.

35. A method for implementing a secure multicast group in a scalable manner, said method including the steps of:

in response to a request from a prospective group member to join the secure multicast group, operating a first device to perform an authorization operation;

upon successful completion of the authorization operation, operating the first device to determine a new group key, and causing the new group key to be sent from the first device to the prospective group member over a unicast communication line and to current members of at least a sub-group of the group over a multicast network; and

in response to a request to cause a first current member of the sub-group to leave said sub-group, operating the first device to determine a second new group key, and causing the second new group key to be sent to current members of the sub-group, other than said first current member, over said multicast network.

36. The method of claim 35, wherein the first device is a trusted intermediary server which communicates with said current members of the sub-group over the multicast network, and wherein the trusted intermediary server communicates with a group security controller over a second multicast network.

37. A method for implementing a secure multicast group in a scalable manner using a system including a group security controller, a first trusted intermediary server which communicates with the group security controller over a first multicast network, a second trusted intermediary server which communicates with the first trusted intermediary server over a second multicast network, and at least a first member which communicates with the second trusted intermediary server over a third multicast network, said method including the steps of:

(a) responding to a request from a prospective group member to join the secure multicast group by operating the second trusted intermediary server to perform an authorization operation; and

(b) upon successful completion of the authorization operation, determining a new group key and sending the new group key to the prospective group member over a unicast communication line and to the first member over the third multicast network.

38. The method of claim 37, wherein the system also includes a second member which communicates with the first trusted intermediary server over the second multicast network, said method also including the steps of:

communicating with the first member over the third multicast network using a first group key; and

communicating with the second member over the second multicast network using a second group key.

39. The method of claim 38, wherein the system also includes a third member which communicates with the group security controller over the first multicast network, and also including the step of:

communicating with the third member over the first multicast network using a third group key.

40. The method of claim 37, wherein the secure multicast group includes a first sub-group which is served by the second trusted intermediary server, and wherein said method also includes the steps of:

in response to a request to cause a first current member of the first sub-group to leave said group, operating the second trusted intermediary server to determine a second new group key, and causing the second new group key to be sent to current members of the first sub-group, other than said first current member, over said third multicast network.

41. A method for adding a new receiver to an existing group of receivers, the group currently receiving data over a multicast network, said data being encrypted with one of a first group key or a third key encrypted with said first group key, and said data being distributed via at least one of a group security controller and a sender, said method comprising the steps of:

transmitting a request to join the existing group of receivers by the new receiver to the group security controller;

performing an authorization procedure which includes supplying a second group key to the new receiver from the group security controller, said authorization procedure being carried out over a unicast communication line;

transmitting the second group key encrypted with the first group key to the existing group of receivers over the multicast network; and

transmitting data over the multicast network encrypted with one of the second group key or a fourth key encrypted with said second group key.

42. A network protocol method for dropping a receiver from a group of receivers, the group currently receiving data over a multicast network encrypted with a first group key, said data being distributed via at least one of a group security controller and a sender, said method comprising the steps of:

generating, at the group security controller, a second group key;

distributing the second group key to each of the receivers remaining in the group; and

transmitting data over the multicast network encrypted with the second group key.