1. Field of the Invention
The invention generally relates to encrypting digital content, and more specifically, to securely locking encrypted digital media to a particular user, computer or other computing device.
2. Background Description
Any owner or distributor of secure or copyrighted digital content, i.e., electronic data in any form, may face several problems concerning the encryption of the data and the method of access that is provided to an end user. The owner or distributor typically is compelled to provide a robust method of encryption while remaining within a system that is relatively easy and simple for users to operate. In order to be relatively effective and/or easy to use, the system provided by owners or distributors must typically allow users to repeatedly access the material while requiring that they undergo an authentication, approval or payment process under a set of rules determined by the content owner. For example, the user may access the content an unlimited number of times after approval, or the user may have to regain approval after a certain number of accesses and/or after a certain amount of time has passed. Normally, content owners require substantial confidence and assurance that once approved for access by a particular user on a particular device the content cannot be freely accessed by another user especially if the content is transmitted to another machine or device.
Currently, most content originators and distributors utilize a Public Key Infrastructure, or PKI system, to accomplish these functions. The PKI system utilizes public key or asymmetric cryptography in which a public key and a private key are produced at the time that the content file is encrypted. This PKI system typically has the following properties or requires the use of:                (i) A certificate authority that issues and verifies a digital certificate. A digital certificate includes the public key, information about the public key or other licensing information.        (ii) A registration authority that acts as the verifier for the certificate authority before a digital certificate is issued to a requestor.        (iii) One or more directories where the certificates (with their public keys) are held.        (iv) A certificate management system.This PKI system is quite complex and very often is an operational and financial burden for content originators, distributors and users.        
An alternative encryption system is symmetric cryptography. A symmetric system utilizes a secret or hidden key that is shared by both the sender and recipient of the encrypted data. While much simpler to use and substantially less costly to implement, a common drawback may be that if the secret key is discovered or intercepted, the encrypted data can easily be decrypted and stolen. However, if a method and system for protecting the secret key, itself, can be provided so that the secret key is not exposed to discovery or interception, including an end user, then a very reliable and effective procedure and system for securely delivering electronic content is possible while avoiding the significant burdens of a PKI infrastructure.