Content scrambling with minimal impact on legacy devices

A method of encrypting a digital television signal, comprising:

• examining unencrypted packets of data in the digital television signal to identify a selected packet type;
• identifying packets as being of the selected packet type to produce first packets;
• duplicating and encrypting duplicates of the packets identified as being of the selected packet type using an encryption method to produce second packets while retaining the first packets in an unencrypted state, the encrypting being carried out at an encrypting device;
• replacing the unencrypted packets of the selected packet type with the first packets and the second packets in the digital television signal to produce a selectively encrypted television signal that contains duplicate packets of the selected packet type with one of the duplicate packets being encrypted while the other of the duplicated packets remains unencrypted;
• and
• broadcasting the selectively dual encrypted television signal.

A television receiver device, comprising:

• a receiver device receiving a digital television signal, where the digital television signal has a plurality of unencrypted packets and a plurality of encrypted packets, where the encrypted packets duplicate some of the unencrypted packets and contain information required to decode the digital television signal;
• a decrypter that decrypts the encrypted packets and drops the transmitted unencrypted version of the same packets;
• and
• a decoder that decodes the unencrypted packets and the decrypted packets to produce a signal suitable for play on a television set.

A method of decoding a selectively encrypted television program, comprising:

• at a receiver device, receiving a selectively encrypted digital television program comprising a plurality of packets, where certain packets of the plurality of packets are encrypted and a remainder of the packets are unencrypted, where the encrypted packets are duplicates of certain of the unencrypted packets that are sent both in encrypted form and in unencrypted form and where the duplicate packets contain information that is required for correct decoding of the television program;
• and
• decrypting the encrypted packets to produce decrypted packets;
• and
• decoding the decrypted packets and the unencrypted packets to produce a decoded television signal.

A television receiver device, comprising:

• a receiver device configured to receive a digital television signal, where the digital television signal has a plurality of unencrypted packets and a plurality of encrypted packets, where the encrypted packets duplicate some of the unencrypted packets and contain information required to decode the digital television signal;
• a decrypter that decrypts the encrypted packets and drops the transmitted unencrypted version of the same packets;
• and
• a decoder that decodes the unencrypted packets and the decrypted packets to produce a signal suitable for play on a television set.