International Business Machines Corporation

Joseph Y Halpern

Cynthia Dwork

Hovey Ramond Strong, Jr

Jeffrey Bruce Lotspiech

Barbara Bluestein Simons

Phillip Adams

An information processing system including an encryption processing logic module and a decryption processing logic module for enabling the encryption of digital information to be decrypted with a decryption key K. The encryption processing module includes logic for encrypting the digital information, distributing the digital information and authorizing a user to decrypt the information. The decryption processing module includes logic for the user to communicate a user number n.sub.i to receive an authorization number a.sub.i from the authorization logic in the encryption processing module and extrication logic for extricating the decryption key. The user number n.sub.i uniquely identifies, and is valuable to, the user, so valuable in fact that the user would be unwilling to publically dislcose it. The extrication logic operates on a digital signet pair (a.sub.i, n.sub.i) consisting of the authorization number and user number, to extract K. The decryption logic then uses K to make the content available to the user. The extrication function is fully available to the user as a publicly-computable function in which it is computationally infeasible to use the extrication function to determine other valid digital signet pairs which can be used to extract K.

Method and system for protection of digital information

An information processing system including an encryption processing logic module and a decryption processing logic module for enabling the encryption of digital information to be decrypted with a decryption key K. The encryption processing module includes logic for encrypting the digital information, distributing the digital information and authorizing a user to decrypt the information. The decryption processing module includes logic for the user to communicate a user number n.sub.i to receive an authorization number a.sub.i (a.sub.i being calculated as equal to ((K.sym.n.sub.i) raised to the power of (1/n.sub.i ' mod .phi. from the authorization logic in the encryption processing module and extrication logic for extricating the decryption key. The user number n.sub.i uniquely identifies, and is valuable to, the user, so valuable in fact that the user would be unwilling to publically disclose it. The extrication logic operates on a digital signet pair (a.sub.i, n.sub.i) consisting of the authorization number and user number, to extract K (K being calculated as equal to ((a.sub.i raised to the power of n.sub.i ') mod N.sym.n.sub.i)). The decryption logic then uses K to make the content available to the user. The extrication function is fully available to the user as a publicly-computable function in which it is computationally infeasible to use the extrication function to determine other valid digital signet pairs which can be used to extract K.

A method and apparatus are disclosed for managing tasks in a network of processors. After a period of time has elapsed, during which the processors of the network have been executing tasks allocated to them, the processors exchange views as to which pending tasks have or have not been completed. The processors reach a consensus as to the overall state of completion of the pending tasks. In a preferred embodiment, the processors exchange views and update their views based on the views received from the other processors. A predetermined condition determines that a consensus has been reached. The predetermined condition is preferably two sets of exchanges in which a processor has received messages from the same set of other processors. Alternatively, the condition is an exchange which does not result in any updates to a processor's view. A processor which has not sent a view as part of an exchange is deemed to have crashed, and the tasks previously allocated to crashed processors are assumed not to have been completed. All pending tasks including those previously allocated but not completed, are then allocated. Preferably, allocation is based on an estimation that approximately the same time will be required for each processor to complete its allocated tasks. Based on this estimation, a time is scheduled for the next exchange of views, and the processors then resume executing their allocated tasks.

Fault tolerant load management system and method

A method and apparatus are disclosed for managing tasks in a network of processors. After a period of time has elapsed, during which the processors of the network have been executing tasks allocated to them, the processors exchange views as to which pending tasks have or have not been completed. The processors reach a consensus as to the overall state of completion of the pending tasks. In a preferred embodiment, the processors exchange views and update their views based on the views received from the other processors. A predetermined condition determines that a consensus has been reached. The predetermined condition is preferably two sets of exchanges in which a processor has received messages from the same set of other processors. Alternatively, the condition is an exchange which does not result in any updates to a processor's view. A processor which has not sent a view as part of an exchange is deemed to have crashed, and the tasks previously allocated to crashed processors are assumed not to have been completed. All pending tasks, including those previously allocated but not completed, are then allocated. Preferably, allocation is based on an estimation that approximately the same time will be required for each processor to complete its allocated tasks. Based on this estimation, a time is scheduled for the next exchange of views, and the processors then resume executing their allocated tasks.

A method for synchronizing clocks in a distributed computing system in the presence of faults. The condition to be renewed guarantees that all clocks of correct processors never deviate by more than some maximum amount. This condition is achieved by periodically resynchronizing the clocks so that the correct clocks do not deviate by more than some minimum deviation. In the process of resynchronization, a correct clock is never adjusted by more than a maximum amount during a period and it is never set back. The method requires ascertaining whether a valid time value message has been received within a specified period. A message is valid if it was received within an interval predetermined as a function of the number of signatures from other processors appending the message. If the valid message has not been received within the current period, then the local processor originates and broadcasts to all processors exactly one time value message and appends thereto its unforgeable signature. On the other hand if a valid message has been received, then the local processor appends its unforgeable signature to the message and passes exactly the one message on by broadcasting to all processors. As part of the protocol involving broadcasting of a message, each processor resets the time for expected resynchronization and updates its local clock.

Decentralized synchronization of clocks

A method for synchronizing clocks in a distributed computing system in the presence of faults. The condition to be renewed guarantees that all clocks of correct processors never deviate by more than some maximum amount. This condition is achieved by periodically resynchronizing the clocks so that the correct clocks do not deviate by more than some minimum deviation. In the process of resynchronization, a correct clock is never adjusted by more than a maximum amount during a period and it is never set back. The method requires that there is a previously agreed upon ordered list of all participants. At a specified time in the period, the first processor on the list attempts to synchronize all to its clock. The result of this is either a synchronization of all correct processors and their clocks to be within the desired tolerance or an agreement among all other correct processors that the first node on the list has failed. If the first fails, then the second tries and so on. Assuming at most f faulty components then one of the first f+1 attempts must succeed.

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Cupertino, CA, United States of America

Joseph Y Halpern