Electrical computers and digital processing systems: support – Multiple computer communication using cryptography – Having particular address related cryptography
Reexamination Certificate
1999-12-22
2004-01-27
Peeso, Thomas R. (Department: 2132)
Electrical computers and digital processing systems: support
Multiple computer communication using cryptography
Having particular address related cryptography
C713S168000, C713S152000, C713S152000
Reexamination Certificate
active
06684331
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to secure network communication systems. The invention relates more specifically to a method and apparatus for distributing and updating group controllers or multicast service agents over a wide area network based on a tree structure.
BACKGROUND OF THE INVENTION
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 the 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 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 an issue. 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 a 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: (1) symmetric algorithms and (2) 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 processor or computer 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. Further, public key encryption systems are vulnerable to chosen-plaintext attacks, particularly when there are relatively few possible encrypted messages.
As a result, a public key cryptosystem generally is utilized to establish a secure data communication channel through key exchanges among the participants. 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. Each party uses the other party's public key value to privately and securely compute a private key, using an agreed-upon algorithm. The parties then use their derived private keys in a separate encryption algorithm to encrypt messages passed over the data communication channel. Conventionally, these private 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 and 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 as follows:
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.
The above 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 sessions 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 be permitted to decrypt the past messages of the multicast group. Another consideration involves making session key updates when a “join” or “leave” occurs; updates must be rapid to prevent undue system delay. This issue relates to how well the network scales to accommodate additional users.
Another conventional technique used to establish secure communication employs a trusted third party authentication mechanism, such as a certificate authority (“CA”) or key distribution center (“KDC”) to regulate the exchange of keys.
FIG. 9
is a block diagram of a system that uses a single central group controller (GC)
901
that has responsibility for distributing, creating, and updating session keys to members of the multicast group (users A-H). The eight users, A-H, communicate with group controller
901
via separate point-to-point connections
903
to obtain a dynamic group session key. The channels
903
can be made secure by using a standard Diffie-Hellman key exchange protocol.
The group controller preferably comes to a shared Group Session key using a binary tree approach. The KDC or CA carries out a third party authentication. The keys can be sent in a multicast or broadcast messages or overlapping broadcast or multicast messages or many point to point messages. Diffie-Hellman is not required to secure communications with the group controller; the binary tree approach provides it. Ideally, onl
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