Michael E Ernst

US Patent:

55861865, Dec 17, 1996

Filed:

Jul 15, 1994

Appl. No.:

8/275500

Inventors:

Gideon A. Yuval - Mercer Island WA
Michael Ernst - Redmond WA

Assignee:

Microsoft Corporation - Redmond WA

International Classification:

H04L 930

US Classification:

380 30

Abstract:

A system for controlling unauthorized access to information distributed to users and, more particularly, for controlling unauthorized access to software distributed to users is provided. One method utilizing the system of the present invention enables the software to be encrypted using a single encryption key and to be decrypted using a multiplicity of "decryption" keys, each of which is unique to a particular user. The "decryption" keys are the products of numeric representations of identifying information relating to users and unique user keys generated using the numeric representations and a "true" decryption key. Since each user receives a unique user key and both the numeric representation and the user key are generated using the identifying information, if the user reveals the numeric representation and the user key (or the product of the numeric representation and the user key), the numeric representation and the user key can be traced to the user who revealed them. Another method utilizing the system of the present invention introduces randomness or pseudo-randomness into the decryption scheme to provide an additional level of security to the scheme.