Cryptographic system for direct broadcast satellite system

Apparatus for encrypting digitized signals in a direct boradcast satellite communications system including a transmission node and a plurality of receiver nodes, each receiver node having an address number and a pre-stored signature key which is a function of its address number, the apparatus comprising:

• means for generating a common key;
• means for encrypting the digitized signals with said common key;
• means for selecting each receiver node in turn, means for generating the signature key for each selected receiver node, said signature key generating means comprising:
• means for storing a master key associated with more than one of the receiver nodes and means for encrypting the address number of said selected receiver node associated with the master key using the master key, means for encrypting said common key for use by the selected receiver node using the generated signature key for that receiver node, said means for generating the signature key for a selected receiver node being actuated in real time to generate the signature key for said selected receiver node each time said receiver node is selected, so as to eliminate the necessity of storing and securing a signature key for each receiver node, means for distributing the encrypted digitized signals and the encrypted common key for said selected receiver node to said selected receiver node by means of a data stream comprising a first portion containing the encrypted digitized signals and receivable by all receiver nodes and a second portion comprising a plurality of sub-portions, each of said sub-portions comprising the encrypted common key for a different receiver node and receivable only by the receiver node having the address number upon which the encrypted common key therein is based.

A cryptographic method for secure distribution of information from a transmission node to first and second receiver nodes, each receiver node having a unique address number, the method comprising the steps of:

• generating a common key;
• encrypting the information to be distributed using said common key:
• selecting each receiver node in sequence;
• generating a different individual key for each receiver node in real time using a master key associated with both of the receiver nodes and encrypting the address number for each receiver node with the master key;
• forming an individualized encrypted common key for each receiver node by encrypting the common key using the generated individual key for that receiver node;
• the individualized key for each receiver node being generated each time that node is selected, so as to eliminate the necessity for storing and securing an individual key for each receiver node;
• and
• distributing the information to all receiver nodes and the individualized encrypted common key for each receiver node to that receiver node.

A method for encrypting digitized signals in a direct broadcast satellite communications system including a transmission node and a plurality of receiver nodes, each receiver node having an address number and a pre-stored signature key which is a function of its address number, the method comprising the steps of:

• storing a master key associated with more than one of the receiver nodes;
• generating a common key;
• encrypting the digitized signals with the common key;
• selecting each receiver node in turn;
• generating the signature key for a selected receiver node by encrypting the address number of the selected receiver node with the master key;
• encrypting said common key for use by the selected receiver node using the generated signature key for that receiver node;
• the signature key for each receiver node being generated in real time each time said receiver node is selected, so as to eliminate the necessity fo storing and securing the generated signature key for each of said receiver nodes, distributing the encrypted digitized signals and the encrypted common key for the selected receiver node to the selected receiver node by generating a data stream comprising a first portion containing the encrypted digitized signals, receivabe by all receiver noes and a second portion comprising a plurality of sub-portions, each of said sub-portions comprising the encrypted common key for a different receiver node and receivable only by the receiver node having the address number upon which the encrypted common key therein is based.