Efficient, secure multicasting with minimal knowledge

Details Efficient, secure multicasting with minimal knowledge Efficient, secure multicasting with minimal knowledge

1998-04-24

2001-02-27

Peeso, Thomas R. (Department: 2767)

Electrical computers and digital processing systems: support

Multiple computer communication using cryptography

Having particular address related cryptography

C713S162000

Reexamination Certificate

active

06195751

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to group data communications, and, more particularly, to secure multi-destination communications over an unsecured communication channel.
2. Relevant Background
Distributed applications such as multimedia conferencing, computer-supported collaborative work, distributed computing, and remote consultation and diagnosis systems for medical applications depend on efficient information exchange among multiple participants. Multi-destination communication and data exchange over a public network are essential for such applications. This type of communication is referred to generally herein as “multicast”. Some applications, generally referred to herein as “broadcasting applications”, are characterized by a small number of sending parties and a large dynamically changing group of receiving parties. Other applications referred to herein as “conferencing applications” involve a large number of sending and receiving participants.
When a group of people want to communicate over a public network such as the Internet in a conference, every message sent out by one of the participants is received by all other participants. The mechanism used to do this communication is called multicast. Any Internet subscriber or user with access to a public network may subscribe to a multicast communication group and will subsequently receive all messages sent to this group. Additionally, any Internet subscriber will be able to send messages to the whole group.
Multicast is rapidly becoming an important mode of communication as well as an effective platform for building group-oriented services. However, to be used for secure or trusted communication, existing multicast techniques must be supplemented by tools for protecting (i.e. encrypting and authenticating) traffic, controlling participation, and restricting access from unauthorized users.
A need for secure electronic information exchange over insecure public networks is increasingly apparent. As compared to conventional unicast, (i.e., point-to-point), multicast is more susceptible to attack. Multicast transmissions present substantially more opportunities for interception of the traffic due to the fact that the message is potentially distributed over a large portion of the network. When an attack occurs, a large number of multicast participants are affected. Further, since multicast addresses are often well known, it becomes easier for an attacker to target an attack. Moreover, multicast typically involves a large number of authorized users which can make it easier for a group of colluding members (or a single attacker posing as a group of legitimate users) to attempt attacks in parallel. While secure unicast communications are well understood, prior attempts at secure multicast communication have difficulty in scaling to large groups and handling groups with highly dynamic membership.
To help achieve secure electronic information exchange, any network security protocol should allow authorized participants to communicate securely over an insecure network under conditions where an attacker is assumed to be able to read, insert, modify, and delete raw communications. Typically, this protocol is achieved by creating a security association between the authorized participants through authentication and key exchange. The security association defines a set of keying material shared only by the authorized participants that can be used for a variety of security objectives such as authentication, confidentiality, and integrity verification.
In a multicast scenario, the security association between participants must be dynamic to support membership changes. A secure multicast communication group must ensure that participants are only allowed to participate during periods when they are authorized. A participant may be authorized to participate in the secure multicast at some periods of time and not authorized to participate during other periods. For example, in a pay-per-view program access a receiver is only authorized for the time periods for which they have paid. The security association and the group keying material it defines must be changed each time a participant joins or leaves the multicast group. This change is necessary to ensure that a joining participant is not able to understand data that was previously multicast and the leaving entity is not able to continue to understand data multicast after its authorization expires. The management and distribution of dynamic security associations and keying material is a fundamental difficulty in a secure multicast protocol.
Practical communication systems must provide reasonable efficiency over the network. By efficiency it is meant that the steps taken to ensure secure communication do not add an inordinate amount of overhead traffic that consumes bandwidth without transferring “payload” information (e.g., application-level data) between participants. For the foreseeable future all communication networks will have some bandwidth limitation which places a premium on efficient communication systems. Hence, it is desirable that the security procedures require minimal communication between participants to perform key management. In fact, in some scenarios such as television or radio broadcast there is only a one-way channel available in which case the need for minimal participant communication is paramount.
Efficiency also means that the steps taken to ensure secure communication do not place an unacceptable computational and data structure burden on the participants. Key management and encryption/decryption processes require participants to perform some additional computation to retrieve a secure communication. These processes also require the participants to implement data structures (i.e., tables, key storage areas, and the like) that may have considerable size. It often occurs that the number, size and/or complexity of these computations and data structures increase as the number of participants in the multicast communication group increases. In many cases, the complexity increases much faster than the number of participants making the security method unscalable because of these computational and data structure costs. Increasing complexity results in poorer performance and/or higher hardware and software costs for each participant entity.
To achieve efficient private communications over the network, all participants in the group need to share a secret information (i.e., key information). The manner of how this secret information is shared and maintained during the lifetime of the group is a focus of the present invention. Prior applications may continuously establish a unicast connections between a sender and all receivers to update security associations and exchange key information. Such continuously required unicast connections are not practical for large groups. For a key change many messages have to be generated or a message has to be processed by intermediate hops which is not efficient. Given a large group where participants may continuously leave and join and where the actual key has to be changed for each leave and join to achieve privacy, computing resources may be insufficient if extensive computation (e.g., such as associated with public key cryptography) is required.
An example of a key management system directed to unicast communications is the simple key management for Internet protocols (SunScreen™ SKIP, (SunScreen is a trademark of Sun Microsystems, Inc.). SKIP is a public key certificate-based key-management scheme which provides group key-management for Internet protocols. Prior multicast implementations of SKIP create a single multicast group and do not handle automatic key changes when participants join and leave the group. Designed to be application independent, SKIP can be plugged into the IP Security Protocol (IPSP) of IPV6. Using certified Diffie/Hellman keys, SKIP obviates the need for real session establishment by holding “soft” session state information that can be discarded and reproduced

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