Patent ID: 7209560

Claim:
A method of distributing digitally encoded data, comprising: a) dividing said data into a multiplicity of frames, b) encrypting said frames, c) distributing multiple copies of the said data frames to a multiplicity of users, each frame being distributed with a control field, d) communicating a seed value for key generation to respective secure modules located at each of the multiplicity of users, e) decrypting the data frames at respective users using keys derived from the seed value communicated to the secure module, the secure module being arranged to enable decryption of a respective frame only when said control field has been passed to the secure module, f) passing a control message, for modifying and controlling the availability of keys, in the control field to the secure module at a selected one or more users, and g) at the secure module of the or each selected user, in response to the said control message, controlling the availability of keys generated from the said seed value, thereby controlling access by the users to the said data.