Patent ID: 7212634
Filing Date: 2007-05-01
Classification: H04L

Abstract:
1. A method of distributing data comprising: (a) encrypting a plurality of data units each with a different one of a first sequence of keys; (b) communicating encrypted data units to a plurality of user terminals; (c) communicating at least one seed value to a user terminal; (d) generating from the seed value or values a second sequence of keys greater in number than the number of seed values communicated to the user terminal; and (e) decrypting data units at the user terminal using said second sequence of keys, characterised in that in step (d) a sequence of keys constituting an arbitrarily doubly bounded portion of the sequence of keys of step (a) is generated, and in that the position in sequence of the lower and upper bounds of the said portion are determined by the at least one seed value communicated in step (c).