Patent ID: RE39166

Claim:
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.