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Encryption using destination addresses in a TDMA satellite communications network

  • US 4,418,425 A
  • Filed: 08/31/1981
  • Issued: 11/29/1983
  • Est. Priority Date: 08/31/1981
  • Status: Expired due to Term
First Claim
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1. In a TDMA satellite communications network having a master station and a plurality of subsidiary earth stations, each communicating through a satellite transponder in a plurality of TDMA frames grouped into superframes, each said station including a TDMA communications controller having a plurality of input/output ports for transferring channels of data from respective, local data users to a TDMA output to said satellite transponder and transferring said channels of data via a TDMA input from said satellite transponder to said respective local users on a time interleaved basis during periodic TDMA frames, an encryption/decryption system for said network, comprising:

  • a superframe initialization vector generator in said master station, having an output connected to said TDMA output thereof, for transmitting a superframe synchronization vector once during each superframe;

    a first encryption engine in each of said stations, having an input connected to said TDMA input thereof, for receiving said superframe synchronization vector and encrypting it with a key, forming a first frame initialization vector prior to a first transmit frame of a transmit superframe, to be used for said first transmit frame;

    a frame initialization vector buffer in each of said stations, having an input connected to said first encryption engine, for storing frame initialization vectors output therefrom;

    a transmit address array buffer in each of said stations, for storing a plurality of destination addresses, each respectively corresponding to each of said plurality of channels of data to be transmitted;

    a first exclusive-OR circuit in each of said stations, having a first input connected to said frame initialization vector buffer and a second input connected to said transmit address array buffer, and an output connected to said input of said first encryption engine, for generating a plurality of channel units of exclusive-OR bits from said first initialization vector and said plurality of destination addresses, each said channel unit corresponding to each of said channels of data to be transmitted;

    said first encryption engine receiving each of said plurality of channel units of exclusive-OR bits and encrypting it with a key, forming a corresponding plurality of channel units of encryption bits;

    a transmit crypto bit buffer in each of said stations, having an alternate A/B storage cycle, with an input connected to said output of said first encryption engine, and an output, for storing said plurality of channel units of encryption bits on a first side during the transmit frame immediately preceding said first transmit frame;

    a second exclusive-OR circuit in each of said stations, having a first input connected to the output of said transmit crypto bit buffer and an output connected to said TDMA output;

    a transmit burst buffer in each of said stations having an alternate A/B storage cycle, with a data input connected to a transmit bus common to the data outputs of all of said ports and an output connected to a second input of said second exclusive-OR circuit, for storing, in clear-text form, said plurality of channels of data on a first side during said transmit frame immediately preceding said first transmit frame;

    said transmit burst buffer bursting said plurality of clear-text data channels from said first side thereof during said first transmit frame, to said second input of said second exclusive-OR circuit synchronously with said transmit crypto bit buffer bursting said plurality of channel units of encryption bits from said first side thereof to said first input of said second exclusive-OR circuit;

    said second exclusive-OR circuit outputting to said TDMA output a resultant plurality of encrypted data channels, each of which is transmitted to said satellite transponder with a corresponding destination address.

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