International Business Machines Corporation

Simeon Naor

Jeffrey Bruce Lotspiech

Dalit Naor

Cynthia Dwork

Shanmugasundaram Ravikumar

Nimrod Megiddo

Dandapani Sivakumar

Ronald Fagin

A tree is used to partition stateless receivers in a broadcast content encryption system into subsets. Two different methods of partitioning are disclosed. When a set of revoked receivers is identified, the revoked receivers define a relatively small cover of the non-revoked receivers by disjoint subsets. Subset keys associated with the subsets are then used to encrypt a session key that in turn is used to encrypt the broadcast content. Only non-revoked receivers can decrypt the session key and, hence, the content.

Method for broadcast encryption and key revocation of stateless receivers

A system and method for aggregating rankings from a plurality of ranking sources to generate a maximally consistent ranking by minimizing a distance measure. The ranking sources may be search engines executing queries on web pages that have been deliberately modified to cause an incorrect estimate of their relevance. The invention supports combining partial rankings.

System and method for aggregating ranking results from various sources to improve the results of web searching

A method for tracing traitor receivers in a broadcast encryption system. The method includes using a false key to encode plural subsets representing receivers in the system. The subsets are derived from a tree using a Subset-Cover system, and the traitor receiver is associated with one or more compromised keys that have been obtained by a potentially cloned pirate receiver. Using a clone of the pirate receiver, the identity of the traitor receiver is determined, or the pirate receiver clones are rendered useless for decrypting data using the compromised key by generating an appropriate set of subsets.

Method for tracing traitor receivers in a broadcast encryption system

An encryption key matrix has rows grouped into segments, with a set of one segment per column establishing a slot. Slots are assigned to device manufacturers, with the keys of the slots then being assigned to decryption devices made by the respective manufacturer. In generating the slots, the number 'q' of segments in a column is first defined such that a predetermined maximum number of devices can be revoked devices (in that all the keys held by the device are revoked) while ensuring that a good device remains a functional device with a probability of at least (1&#x2212;Q), wherein Q is a predefined device confidence. Once the number 'q' of segments has been defined, the slots themselves are defined in a provably non-discriminatory fashion using an error-correcting code such as a Reed-Solomon code. With this invention, overlap between slots can be minimized to minimize the possibility that the key set of an innocent device might be inadvertently revoked when the keys in the slots of a &#x201c;bad&#x201d; manufacturer are revoked.

Method for assigning encryption keys

A method is provided for authentication of encrypted messages. A non-malleable public-key encryption technique is employed, so that an eavesdropper cannot employ an encrypted message, previously overheard, to generate a message which, when sent to a recipient, which would pass as a message originating from a valid sender. In a preferred embodiment, a protocol is provided in which, in response to a message authentication request from a sender, a recipient sends the sender a string, encrypted according to the sender's non-malleable public key. The sender decrypts the string using its private key, and sends the recipient a message which is a function of the string and the message to be authenticated. Because of the non-malleability of the public keys, an eavesdropper cannot impersonate the sender or the recipient and produce a disinformation message which would nevertheless contain the correct authorization string.

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Palo Alto, CA, United States of America

Simeon Naor