Patent ID: 7356688

Claim:
A method for encrypting an original document for distribution to a selected recipient chosen from a plurality of possible recipients, comprising the steps of: generating a session key based on a random number privately maintained only by the owner, including an encryptor, of the original document; encrypting the original document with the session key to create an encrypted document; generating a proxy key based on a public key corresponding to the selected recipient, wherein the proxy key may be published without compromising its security, and wherein the proxy key, when applied to a document encrypted for a recipient, is used to transform the document into a document encrypted for another recipient without decrypting the message in the process; and applying the proxy key to the encrypted document to transform the encrypted document into a transformed document, wherein the transformation may occur in a trusted environment without compromising its security, wherein the transformation may occur in an untrusted environment without compromising its security, and wherein the encrypted document remains in an encrypted state while being transformed into the transformed document and is not decrypted to the original document and re-encrypted at any point during the transformation.