Time division partial encryption

A method of encrypting an unencrypted television program, comprising:

• sampling the unencrypted television program at a specified time interval;
• for each sample, encrypting the sample according to a first encryption method to create a first encrypted sample for the television program and encrypting the sample according to a second encryption method to create a second encrypted sample for the television program;
• and
• combining the first encrypted samples with the unsampled portions of the unencrypted television program to produce a multiple partially encrypted television program as an encrypted output signal.

A method of encrypting an unencrypted television program, comprising:

• identifying N periods out of every M periods of the television program for encryption, where M is greater than N;
• encrypting the N periods out of every M periods of the television program according to a first encryption method,
• encrypting the N periods out of every M periods of the television program according to a second encryption method;
• and
• combining the first and second encrypted periods with unencrypted periods to produce a partially multiple encrypted television program to produce a multiple selectively encrypted output signal.

A method of decoding a television program, comprising:

• receiving a television signal having N periods out of every M periods of the television program encrypted according to a first encryption method, where M is greater than N, and wherein the same N periods of the television program are encrypted according to a second encryption method, wherein M–N periods are unencrypted;
• decrypting the N periods according to a first decryption method to produce decrypted periods;
• discarding the N periods encrypted according to the second encryption method;
• and
• decoding the decrypted periods and the unencrypted periods.

A television set-top box for decoding a television program, comprising:

• a receiver receiving a television program having N periods out of every M periods of the television program encrypted according to a first encryption method, where M is greater than N, and wherein the same N periods of the television program encrypted according to a second encryption method, wherein M–N periods are unencrypted;
• a decrypter that decrypts the N periods according to a first decryption method to produce decrypted periods;
• filtering means for discarding the N periods encrypted according to the second encryption method;
• and
• a decoder that decodes the decrypted periods and the unencrypted periods.

A method of encrypting a plurality of unencrypted television program, comprising:

• selecting a video frame from each unencrypted television program at a specified time interval;
• encrypting the frame according to a first encryption method to create a first encrypted frame for each television program;
• encrypting the frame according to a second encryption method to create a second encrypted frame for each television program;
• and
• combining the first and second encrypted frames with unencrypted frames of the unencrypted television programs to produce partially dual encrypted television programs as an encrypted output signal.

A method of encrypting an unencrypted television program, comprising:

• selecting a frame of the unencrypted television program at a specified time interval;
• encrypting the frame according to a first encryption method to create a first encrypted sample for the television program;
• encrypting the frame according to a second encryption method to create a second encrypted sample for the television program;
• and
• combining the first encrypted sample and the second encrypted sample with unencrypted portions of the television program to produce a multiple partially encrypted television program.