The proliferation of network computing has shaped how society conducts business and personal communication. As reliance on computer networks grows, the flow of information between computers continues to increase in dramatic fashion. Accompanying this increased flow of information is a proportionate concern for network security. Commercial users, who regularly conduct business involving the exchange of confidential or company proprietary information over their computer networks, demand that such information is secure against interception by an unauthorized party or to intentional corruption. In addition, with the acceptance of electronic commerce over the global Internet, all users recognize the critical role cryptographic systems play in maintaining the integrity of network communication.
Cryptography is the art and science of keeping messages secure. A message is information or data that is arranged or formatted in a particular way. In general, a message, sometimes referred to as “plaintext” or “cleartext,” is encrypted or transformed using a cipher to create “ciphertext,” which disguises the message in such a way as to hide its substance. In the context of cryptography, a cipher is a mathematical function that can be computed by a data processor. Once received by the intended recipient, the ciphertext is decrypted to convert the ciphertext back into plaintext. Ideally, ciphertext sufficiently disguises a message in such a way that even if the ciphertext is obtained by an unintended recipient, the substance of the message cannot be discerned from the ciphertext.
Many different encryption/decryption approaches for protecting information exist. In general, the selection of an encryption/decryption scheme depends upon considerations such as the types of communications to be made more secure, the particular parameters of the network environment in which the security is to be implemented, and the desired level of security. An important consideration is the particular system on which a security scheme is to be implemented since the level of security often has a direct effect on system resources.
For example, for small applications that require a relatively low level of security, a traditional restricted algorithm approach may be appropriate. With a restricted algorithm approach, a group of participants agree to use a specific, predetermined algorithm to encrypt and decrypt messages exchanged among the participants. Because the algorithm is maintained in secret, a relatively simple algorithm may be used. However, in the event that the secrecy of the algorithm is compromised, the algorithm must be changed to preserve secure communication among the participants. Scalability, under this approach, is a problem. As the number of participants increases, keeping the algorithm secret and updating it when compromises occur place an undue strain on network resources. In addition, standard algorithms cannot be used since each group of participants must have its own unique algorithm.
To address the shortcomings of traditional restricted algorithm approaches, many contemporary cryptography approaches use a key-based algorithm. Generally two types of key-based algorithms exist: symmetric algorithms and asymmetric algorithms, of which one example is a public key algorithm. As a practical matter, a “key” forms one of the inputs to a mathematical function that is used by a computer or processor to generate a ciphertext.
Public key algorithms are designed so that the key used for encryption is different than the key used for decryption. These algorithms are premised on the fact that the decryption key cannot be determined from the encryption key, at least not in any reasonable amount of time with practical computing resources. Typically, the encryption key (public key) is made public so that anyone, including an eavesdropper, can use the public key to encrypt a message. However, only a specific participant in possession of the decryption key (private key) can decrypt the message.
Public key algorithms, however, often are not employed as a mechanism to encrypt messages, largely because such algorithms consume an inordinate amount of system resources and time to encrypt entire messages.
As a result, a public key cryptosystem is utilized to establish a secure data communication channel through key exchanges among the participants. That is, two or more parties, who wish to communicate over a secure channel, exchange or make available to each other public (or non-secure) key values. In the Diffie-Hellman algorithm, each party uses the other party's public key value to privately and securely compute a secret key, using an agreed-upon algorithm. The parties then use their derived secret keys in a separate encryption algorithm to encrypt messages passed over the data communication channel. Conventionally, these secret keys are valid only on a per communication session basis, and thus, are referred to as session keys. These session keys can be used to encrypt/decrypt a specified number of messages or for a specified period of time.
A typical scenario involves participants, A, B, in which user A is considered a publisher of a message to a subscriber, user B. The public key algorithm used to establish a secure channel between publisher, A, and subscriber, B, is:                1. B provides a public key, B, to A.        2. A generates a random session key SK, encrypts it using public key B and sends it to B.        3. B decrypts the message using private key, b (to recover the session key SK).        4. Both A and B use the session key SK to encrypt their communications with each other; after the communication session, A and B discard SK.This approach provides the added security of destroying the session key at the end of a session, thereby, providing greater protection against eavesdroppers.        
Once a multicast group is established, management of the session's keys due to membership changes poses a number of problems. Forward secrecy, which arises when a member node leaves the multicast group and may still possess the capability to decipher future messages exchanged among the group, becomes a concern. In addition, in the case where a new member node enters the multicast group, the new member should not, in general, be permitted to decrypt the past messages of the multicast group. Another consideration involves the expediency of session key updates when a “join” or “leave” occurs, as not to inject undue system delay. This issue relates to how well the network scales to accommodate additional users.
FIG. 1 is a block diagram of one approach to establish secure communication that employs a third party, called a key distribution center (KDC), to regulate the exchange of keys. A single central group controller (GC) 1001 is responsible for distributing, creating, and updating session keys to the members of the multicast group comprising users A-H. The users A-H communicate with the group controller 1001 via separate point-to-point connections 1003 to obtain the dynamic group session key.
Channels 1003 can be made secure by using a standard Diffie-Hellman key exchange protocol. To set up the secured channel among the nodes, N-1 messages are exchanged, wherein N is the number of nodes. Although this is relatively low overhead in terms of the number of messages that are exchanged, a major drawback is that the centralized group controller 1001 represents a single point of failure, so that the system lacks fault tolerance. If the group controller 1001 is down, no secure communication can exist among the multicast group of users A-H. This is unacceptable, especially in mission critical systems.
Another drawback is that the group controller 1001 is a potential bottleneck in the network. For instance, if multiple nodes request to join the multicast group, the group controller 1001 may not be able to process such requests in a timely manner; this problem is especially pronounced if the multicast group is distributed over a wide area network (WAN).
Further, the group controller 1001 does not scale well, due, in part, to physical hardware constraints.
Network entities share information in a variety of ways. One mechanism for sharing keys in a network involves use of a directory. A known standard for directory services is the X.500 standard, which was developed by the ITU (International Telecommunications Union). Directories traditionally provide services such as white pages to track e-mail addresses along with other user information (e.g., telephone and fax numbers) on a global scale. Conventional implementations of directories lack an integrated security mechanism with the network entities.
Based upon the foregoing, there is a clear need for improved approaches to key exchange that eliminates single points of failures, especially among broadcast or multicast group members.
In particular, there is an acute need for an improved approach to enhance scalability and fault tolerance, particularly over a WAN.
There is also a need for integrating directory services with security network mechanisms.
Based on the need to provide secure communication while limiting the adverse effects on system resources and the limitations in the prior approaches, an approach for providing secure communication that provides a relatively high level of security while requiring relatively fewer system resources and time to perform is highly desirable.