External security module for a television signal decoder

• US 5,029,207 A
• Filed: 02/01/1990
• Issued: 07/02/1991
• Est. Priority Date: 02/01/1990
• Status: Expired

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Inventors: Gammie, Keith B.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Cain, David
• Application Number:
  US07/473,442
• Time in Patent Office: 516 Days
• Field of Search: 380/10, 380/16, 380/21, 380/43, 380/23, 380/45
• US Class Current: 380/228
• CPC Class Codes: H04N 7/1675 Providing digital key or authorisation information for generation or regeneration of the scrambling sequence pseudo-random number generators in general G06F7/58

Abstract

A decoder for descrambling encoded satellite transmissions comprises an internal security element and a replaceable security module. The program signal is scrambled with a key and then the key itself is twice-encrypted and multiplexed with the scrambled program signal. The key is first encrypted with a first secret serial number (SSN₁) which is assigned to a given replaceable security module. The key is then encrypted with a second secret serial number (SSN₀) which is assigned to a given decoder. The decoder performs a first key decryption using the second secret serial number (SSN₀) stored within the decoder. The partially decrypted key is then further decrypted by the replaceable security module using the first secret serial number (SSN₁) stored within the replaceable security module. The decoder then descrambles the program using the twice-decrypted key. The replaceable security module can be replaced, allowing the security system to be upgraded or changed following a system breach.

Claims

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 encrypted key using a second confidential serial number and outputting a 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 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 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 key and outputting a descrambled signal.

2. The security system of claim 1, wherein said encoder means further comprises:

key memory means coupled to said signal scrambling means and said first key encryptor means for storing said key.

3. The security system of claim 1, wherein said encoder means further comprises:

a first confidential serial number database coupled to said first key encryptor means, containing a list of first confidential serial numbers.

4. The security system of claim 3, wherein said encoder means further comprises:

a second confidential serial number database coupled to said second key encryptor means, containing a list of second confidential serial numbers.

5. The security system of claim 1, wherein said decoder means further comprises:

second confidential serial number memory means coupled to said first key decryptor means, for storing a second confidential serial number.

6. The security system of claim 5, wherein said replaceable security module contains said first confidential serial number memory means.

9. The security system of claim 1, wherein said decoder means further comprises:

telephone interface means for transmitting and receiving data to and from a pay television provider, said data encrypted with a confidential telephone number.

10. The security system of claim 9, wherein an encrypted key is received via said telephone interface means.

11. The security system of claim 1, wherein said transmission means further comprises:

first transmission means for transmitting said scrambled signal, and

second transmission means for transmitting said twice-encrypted key.

12. The security system of claim 1, wherein said signal is a television signal.

13. The security system of claim 11, wherein said television signal is a B-MAC type television signal.

14. The security system of claim 1, wherein said encoder means further comprises:

multiplexor means for multiplexing said twice-encrypted key with said scrambled signal prior to transmission.

15. The security system of claim 14, wherein said decoder further comprises:

demultiplexor means for demultiplexing said twice-encrypted key from said scrambled signal.

7. A security system for transmission of a signal comporising:

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 encrypted key using a second confidential serial number and outputting a twice-encrypted key,

decoder means coupled to said transmission means for receiving and descrambling said scrambled signal, said decoder means comprising;

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

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 first confidential serial number and outputting a decrypted key, and

signal descrambling means coupled to said first second key decryptor means and said transmission means for descrambling said scrambled signal using said twice-decrypted key and outputting a descrambled signal.

8. The security system of claim 7, wherein said decoder means further comprises:

first confidential serial number memory means coupled to said second key decryptor means for storing a first confidential serial number.

16. A decoder for receiving and descrambling a signal which has been scrambled using a key which has been subsequently twice-encrypted, said decoder comprising:

first key decryptor means for performing a first key decryption on said twice encrypted key using said second confidential serial number and outputting a partially decrypted key,

a replaceable security module, removably attached to said decoder 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 first confidential serial number and outputting a decrypted key, and

signal descrambling means coupled to said second key decryptor means for descrambling said scrambled signal using said twice-decrypted key and outputting a descrambled signal.

17. The decoder of claim 16, further comprising:

key memory means coupled to said signal descrambler means and said second key decryptor means for storing said decrypted key.

18. The decoder of claim 16, further comprising:

second confidential serial number memory means coupled to said first key decryptor means, for storing a second confidential serial number.

20. The decoder of claim 16, further comprising:

first confidential serial number memory means coupled to said second key decryptor means, for storing a first confidential serial number.

21. The decoder of claim 20, wherein said replaceable security module contains first confidential serial number memory means.

22. The decoder of claim 16, wherein said signal is a television signal.

23. The decoder of claim 16 further comprising:

telephone interface means for transmitting and receiving data to and from a pay television provider, said data encrypted with a confidential telephone number.

24. The decoder of claim 23, wherein said twice-encrypted key is received via said telephone interface means.

25. The decoder of claim 22, wherein said television signal is a B-MAC type television signal.

26. The decoder of claim 16, wherein said scrambled signal and said twice-encrypted key have been multiplexed together prior to reception by the decoder.

27. The decoder of claim 24, further comprising:

demultiplexor means for demultiplexing said twice-encrypted key from said scrambled signal.

19. A decoder for receiving and descrambling a signal which has been scrambled using a key which has been subsequently twice-encrypted, said decoder comprising:

a replaceable security module, removably attached to said decoder and containing a first key decryptor means for performing a first key decryption on said twice encrypted key using said second confidential serial number and outputting a partially decrypted key,

second key decryptor means coupled to said first key decryptor means for performing a second key decryption on said partially decrypted key using a first confidential serial number and outputting a decrypted key, and

signal descrambling means coupled to said second key decryptor means for descrambling said scrambled signal using said twice-decrypted key and outputting a descrambled signal.

28. A method of transmitting a secure signal comprising the steps of:

scrambling said signal using a key to produce a scrambled signal,

encrypting said key using a first confidential serial number to produce a once-encrypted key.

further encrypting said once encrypted key using a second confidential serial number to produce a twice-encrypted key,

transmitting said scrambled signal and said twice-encrypted key,

receiving said scrambled signal and said twice-encrypted key in a decoder,

performing a first decryption of said twice-encrypted key using said second confidential serial number to produce a partially decrypted key,

performing a second decryption on said partially decrypted key in a replaceable security module removably attached to said decoder using a first confidential serial number to produce a decrypted key,

descrambling said scrambled signal using said decrypted key to produce a descrambled signal, and

outputting said descrambled signal.

29. The method of claim 28, wherein said second confidential security number is assigned to said decoder.

32. The method of claim 28, wherein said first confidential security number is assigned to said replaceable security module.

33. The method of claim 28, wherein said transmitting step further comprises:

multiplexing said scrambled signal and twice-encrypted key together prior to transmission.

34. The method of claim 28, wherein said transmitting step further comprises:

transmitting said scrambling signal and said twice-encrypted key as separate signals.

30. A method of transmitting a secure signal comprising the steps of:

scrambling said signal using a key to produce a scrambled signal,

encrypting said key using a first confidential serial number to produce a once-encrypted key,

further encrypting said once encrypted key using a second confidential serial number to produce a twice-encrypted key,

transmitting said scrambled signal and said twice-encrypted key,

receiving said scrambled signal and said twice-encrypted key in a decoder,

performing a first decryption of said twice-encrypted key in a replaceable security module removably attached to said decoder using said second confidential serial number to produce a partially decrypted key,

performing a second decryption on said partially decrypted key using a first confidential serial number to produce a decrypted key,

descrambling said scrambled signal using said decrypted key to produce a descrambled signal, and

outputting said descrambled signal.

31. The method of claim 30, wherein said second confidential security number is assigned to said replaceable security module.

35. A method of decoding a signal comprising the steps of:

receiving a scrambled signal and a twice-encrypted key in a decoder,

performing a first decryption of said twice-encrypted key using a second confidential serial number to produce a partially decrypted key,

performing a second decryption on said partially decrypted key in a replaceable security module removably attached to said decoder using a first confidential serial number to produce a decrypted key,

descrambling said scrambled signal using said decrypted key to produce a descrambled signal, and

outputting said descrambled signal.

39. The method of claim 35, wherein said second confidential serial number is assigned to said decoder.

40. The method of claim 35, wherein said first confidential serial number is assigned to said replaceable security module.

36. A method of decoding a signal comprising the steps of:

receiving a scrambled signal and a twice-encrypted key in a decoder,

performing a first decryption of said twice-encrypted key in a replaceable security module removably attached to said decoder using a

second confidential serial number to produce a partially decrypted key,

performing a second decryption on said partially decrypted key using a first confidential serial number to produce a decrypted key,

descrambling said scrambled signal using said decrypted key to produce a descrambled signal, and

outputting said descrambled signal.

37. The method of claim 36 wherein said first confidential serial number is assigned to said decoder.

38. The method of claim 36, wherein said second confidential serial number is assigned to said replaceable security module.

41. A decoder for receiving and descrambling a signal scrambled using a twice-encrypted key, said decoder comprising:

connector means for connecting said decoder to a replaceable security module, through which connector means said twice-encrypted key is transmitted to said replaceable security module and a partially-decrypted key is received from said replaceable security module,

key decryptor means, coupled to said connector means for performing a decryption on said partially-decrypted key using a second confidential serial number, and outputting a decrypted key, and

signal descrambling means coupled to said key decryptor for descrambling said signal with said decrypted key and outputting a descrambled signal.

42. The decoder of claim 41, further comprising:

key memory means coupled to said signal descrambling means and said key decryptor means for storing said decrypted key.

43. The decoder of claim 41, wherein said signal is a television signal.

44. The decoder of claim 41, wherein said television signal is a B-MAC type television signal.

45. The decoder of claim 41, wherein said scrambled signal and said twice-encrypted key signal have been multiplexed together prior to reception by the decoder.

46. The decoder of claim 45, further comprising:

demultiplexor means for demultiplexing said twice-encrypted key signal from said scrambled signal.

47. The decoder of claim 41, further comprising:

telephone interface means for transmitting and receiving data to and from a pay television provider, said data encrypted with a confidential telephone number.

48. The decoder of claim 47, wherein said twice-encrypted key is received via said telephone interface means.

49. A decoder for receiving and descrambling a signal scrambled using a twice-encrypted key, said decoder comprising:

key decryptor means, for performing a first key decryption on said twice-encrypted key using a first confidential serial number and outputting a partially decrypted key,

connector means, coupled to said key decryptor means for connecting said decoder to a replaceable security module, through which connector means said partially decrypted key is transmitted to said replaceable security module and a descrambling control signal is received from said replaceable security module,

signal descrambling means, coupled to said connector means and receiving said descrambling control signal for descrambling said signal and outputting a descrambled signal.

50. The decoder of claim 49, wherein said signal is a television signal.

51. The decoder of claim 49, wherein said television signal is a B-MAC type television signal.

52. The decoder of claim 49, wherein said scrambled signal and said twice-encrypted key signal have been multiplexed together prior to reception by the decoder.

53. The decoder of claim 52, further comprising:

demultiplexor means for demultiplexing said twice-encrypted key signal from said scrambled signal.

54. The decoder of claim 49 further comprising:

telephone interface means for transmitting and receiving data to and from a pay television provider, said data encrypted with a confidential telephone number.

55. The decoder of claim 54, wherein said twice-encrypted key is received via said telephone interface means.

56. A replaceable security module for storing confidential serial number and performing a partial decryption of a twice-encrypted key and outputting a partially decrypted key, said replaceable security module comprising;

connector means for connecting said replaceable security module to a decoder and through which a twice-encrypted key is received from said encoder and a partially decrypted key is transmitted to said decoder,

memory means for storing at least a confidential serial number, and

decryption means, coupled to said connector means and said memory means for performing a partial decryption on said twice-encrypted key and outputting a partially-decrypted key.

57. The replaceable security module of claim 56, wherein said memory means further comprises:

security means for allowing the contents of said memory means to be read only by said decryption means.

58. A replaceable security module for storing a secret serial number and performing a decryption of a partially decrypted key and outputting a descrambling control signal, said replaceable security module comprising;

connector means for connecting said replaceable security module to a decoder and through which a partially decrypted key is received from said encoder and descrambling control signal is transmitted to said decoder,

memory means for storing at least a secret serial number, and

decryption means, coupled to said connector means and said memory means for performing a decryption on said partially decrypted key and outputting a descrambling control signal.

59. The replaceable security module of claim 58, wherein said memory means further comprises:

security means for allowing the contents of said memory means to be read only by said decryption means.