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External security module for a television signal decoder

  • US RE39,166 E1
  • Filed: 05/04/1993
  • Issued: 07/11/2006
  • Est. Priority Date: 02/01/1990
  • Status: Expired due to Term
First Claim
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1. A security system for transmission of a signal comprising:

  • encoder means for encoding said signal, said encoder means comprising;

    signal scrambling means for scrambling signal and outputting a scrambled signal and a key for descrambling said scrambled signal;

    first key encryptor means coupled to said signal scrambling means, for performing a first encryption on said key using a first confidential serial number and outputting a once-encrypted key, and second key encryptor means coupled to said first key encryptor means, for performing a further encryption on said once once-encrypted key using a second confidential serial number and outputting a twice-encrypted key, transmission means coupled to said signal scrambling means and said second key encrypted means for transmitting said scrambled signal and said twice-encrypted key, decoder means coupled to said transmission means for receiving and descrambling said scrambled signal, said decoder means comprising;

    first key decryptor means coupled to said transmission means, for performing a first key decryption on said twice twice-encrypted key using said second confidential serial number and outputting a partially decrypted key, a replaceable security module, removably attached to said decoder means and containing a second key decryptor means coupled to said first key decryptor means, for performing a second key decryption on said partially decrypted key using a said first confidential serial number and outputting a decrypted key, and signal descrambling means coupled to said second key decryptor means and said transmission means for descrambling said scrambled signal using said twice-decrypted decrypted key and outputting a descrambled signal.

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