Copy prevention method and apparatus for digital video system

Abstract

A copy prevention method and apparatus for a digital video system is disclosed including the steps of: (a) adding a header area of a header start code and key field to a reproduced bit stream: stream; (b) decrypting and transmitting the bit stream to which the header area is added: added; (c) detecting a key field of the decrypted and transmitted bit stream and detecting copy prevention information; and (d) encrypting the bit stream according to information detected from stop step (c) and optionally recording it an on a tape.

Description

to respect6 5 comprises a PES header detecting portion 10 for searching the parallel data in synchronization with a clock clk to detect the PES header, and a copy prevention information extractor 20 enabled by the PES header signal of PES header detecting portion 10 to detect the copy prevention information field.

Referring to FIG. 7, PES header detecting portion 10 comprises first and second flipflops 11 and 12 for sequentially delaying the parallel data according to clock elk clk, a packet start code detector 13 for searching the parallel data and the output of first and second flipflops 11 and 12 to detect the packet start code of the PES header, a stream ID detector 14 for searching the output of second flipflop 12 to detect the stream ID of the PES header, a delay 15 for sequentially delaying the output is-pscp of packet start code detector 13 according to clock clk, and a detection signal generator 16 for logically multiplying the outputs of delay 15 and stream ID detector 14 and outputting a PES header detection signal is-PES-header.

As shown in FIG. 9, copy prevention information extractor 20 comprises a D-flipflop 21 for holding the parallel data output from PES header detector 10, a D-flipflop 22 for holding PES header detection signal is-PES-header of PES header detector 10, a D-flipflop 23 cleared by the output of D-flipflop 22 and holding voltage (+5V) by a CR signal of the output of D-flipflop 21 and outputting a signal LCR, a D-flipflop 24 cleared by the output of D-flipflop 22 and holding voltage (+5V) by an OC signal of the output of D-flipflop 21 and outputting a signal LOR LOC, a copy prevention information position operator 25 for searching the parallel data of PES header detector 10 and calculating the position of an additional copy information field, a counter 26 for counting the output of copy information position operator 25, and a D-flipflop 27 for holding the additional copy information field of the output of D-flipflop 21.

The operation and effect of the present invention will be explained below. Generally, in case of reproducing or copy recording data on tapa tape, connections between systems are made as shown in FIG. 4.

With those connections, an MPEG bit stream reproduced from VCR A is input to a satellite receiver or high-definition TV so that it cannot be recognized whether the stream is displayed on a screen or input to VCR B and recorded on another video tape.

For this reason, according to the present invention, in case that the bit stream reproduced from VCR A is copied from VCR B, information on copy prevention is transmitted to VCR B from VCR A. VCR B analyzes this information which is recorded with the bit stream.

Here, the insertion position of the copy prevention information contained in a GA bit stream is very limited because it must not affect decoding of the decoder of the satellite receiver or high-definition TV so that an image is displayed normally on a monitor. The copy prevention information may be inserted into the front end of the MPEG bit stream or inside the PES header.

When the MPEG bit stream is decoded in units or of group of picture (GOP), the respective GOPs are classified by their cop GOP start codes. This is useful in transmitting initialization data to a recording-side VCR because decoding is never affected even when a slight amount of data is added to the front end of the MPEG bit stream.

The case of inserting the copy prevention information into the PES header is useful in repeated transmission of information because copy prevention of a recording medium such as DSM is decided using CR and OC flaps of the PES header and additional copy information field. In this case, there are a variety of copy preventing methods.

First, when a mode of “No Copy” is detected from the additional copy information field of the PES header, VCR B is not able to enter its recording mode.

Second, when a mode of “Copy Permitted” is detected in order to implement a copy prevention such as DAT mode, VCR B records but “No Copy” mode is recorded in the additional copy information field to interrupt recopying from a copying tape. This means that a secondary source tape can be made, but a third source tape cannot.

Third, for “Back-up Copy”, tape B copied from VCR B is reproducible normally only in VCR A. According to this method, reproducing-side VCR A encrypts the bit stream with its own inherent key and records it on tape so that only reproducing-side VCR A decrypts the MPEG bit stream recording on the tape. For every VCR set, a unique key is provided, encrypted by VCR's key and recorded on tape B. However, the VCR set for recording tape B is VCR B and tape B is encrypted by VCR A's key so that VCR A's key needs to be transmitted to VCR B with GA bit stream.

Accordingly, when the key information of VCR A is transmitted as a header in advance prior to the bit stream in the “Back-up Copy”, it is recorded at the front end of tape B, which satisfies the insertion position of the copy prevention information mentioned before.

Here, as shown in FIG. 2, the position of the additional copy information field is varied within the PES header according to whether presentation time stamp (PTS)/Decoding time stamp (DTS) and DSM trick mode field are present or not. This varied position must be compensated. Here, information transmitted through the additional copy information is a copy prevention method to be performed by recording-side VCR B.

In case of recording the bit stream shown in FIG. 11A in the method of “Back-up Copy”, the format of the bit stream recorded on tape is determined as shown in FIG. 11B.

Here, a header area added to the front of the MPEG bit stream is formed with a tape header start code, that is, the header identifier code, and a key field for storing key information. In case of encrypting the MPEG bit stream in units of GOP, encryption blocks are classified by the packet start code prefix and stream ID of the PES header. The encryption block is a basic unit of encryption and can change whether encryption is performed in units of the encryption block, and encryption algorithm and key selection. Here, the encryption blocks must not be encrypted until the additional copy information field of the PES header. Encryption is performed until the end of the encryption block after the additional copy information field. The first ‘transmission header’ is not encrypted.

The operation of performing the “back-up Copy” mode by adding the header will be described below.

First, in copying, when recording data of tape A is encrypted, reproducing-side VCR A decrypts it using the key information of the key field so as to make message m. Its key information is added to the header and transmitted in the format of FIG. 11C.

Recording-side VCR B records the key information transmitted from reproducing-side VCR A on the header of copying tape B and then records the encrypted bit stream. Here, when the key information is transmitted from reproducing side to recording side, for security, a public-key encryption may be employed to the system because the information may be exposed to a pirate.

Such public-key encryption system ensures the secret of data even though the public-key is exposed but cannot be processed in real-time due to a great amount of calculation. Therefore, this system is not improper when the MPEG bit stream is encrypted directly. The “Back-up Copy” can be implemented when the MPEG bit stream is encrypted using a block-cipher algorithm or stream-cipher algorithm such as DES and a key used is encrypted in the public-key encryption.

In this case, every VCR u incorporates encryption algorithm E^PK_U corresponding to the public-key and decryption algorithm D^PK_U corresponding to the secret key. Encryption algorithm E^PK_U takes a power key of VCR u, and decryption algorithm D^PK_U to an internal key of VCR u.

Here, the internal key may be opened to the public. Reproducing-side VCR A transmits the internal key on the key field of the header because another VCR encrypts using the internal key. Recording-side VCR B randomly selects a key Y used in the block-cipher algorithm such as DES and encrypts it with the public-key encryption system using an external key E^PK_A. The result is recorded on the key field of copying tape B.

Sequentially, the data is divided into encryption blocks and encrypted and recorded in the block-cipher algorithm using key Y. In this method, the bit stream of FIG. 11D is recorded on copying tape B.

When copying tape B is reproduced in reproducing-side VCR A, key Y can be restored by decryption D^PK_A[E^PK_A(Y)] in which data is decrypted properly. In other VCRs, key Y cannot be found, which disables the decryption of the bit stream.

As An embodiment of the present invention, shown in FIG. 5, for performing such an operation will be described below.

When playback starts for tape copying, reproducing portion 1 detects data recorded on tape as shown in FIG. 11A, and amplifies it by a predetermined level. As shown in FIG. 11B, key inserting portion 2 adds a header having a tape header start code and key field to the GA bit stream of reproducing portion 1 shown in FIG. 11A. Copy prevention information is loaded on the additional copy information field of the PES header to form a format shown in FIG. 11C. Here, decrypting portion 3 decrypts the bit stream formed in key inserting portion 2 and transmits it as parallel data to the recording-side VCR via an interface.

When the bit stream of FIG. 11C is transmitted to the recording-side VCR via the interface, key detecting/correcting portion 4 detects the key field added to the bit stream and corrects the key field if necessary.

Copying prevention information detecting portion 5 searches the PES header area to detect the additional copy information field. Here, though a slight amount of information is recorded in the additional copy information field, redundancy is provided in several areas of the bit stream to increase reliability of information transmitted.

Copy prevention information detecting portion 5 extracts the value of AC flag from the PES header flag in order to calculate the position of the additional copy information field because it varies within the PES header. Here, when copy prevention information correcting portion 6 corrects the output of copy prevention information detecting portion 5, encrypting portion 7 performs encrypting using the block-cipher algorithm such as DES. Here, copy prevention information correcting portion 6 performs correction while the input data is stored in a RAM. Accordingly, encrypting portion 7 records the encrypted bit stream on tape in recording portion 8. Because the key information of the reproducing-side VCR is added on the copying tape, only a VCR having this key information can reproduce tape normally.

As shown in FIG. 6, in copy prevention information detecting portion 5, PES header detecting portion 10 searches the output of key detecting/correcting portion 4 and outputs a header detection signal is-PES-header. After header detection signal is-PES-header is input, copy prevention information extractor 20 detects the additional copy information field and OC and CR flags.

PES header detector 10 for detecting the PES header is formed as shown in FIG. 7. When bit stream data_in is input as shown in FIG. 8A, first flipflop 11 synchronized to clock clk is delayed for a predetermined time to output the bit stream delayed as shown in FIG. 8B. Second flipflop 12 delays the output of first flipflop 11 by are predetermined time and outputs the bit stream delayed as shown in FIG. 8C.

Here, packet start code detecting portion 13 searches the bit stream shown in FIG. 8A and the output of first and second flipflops 11 and 12 shown in FIGS. 8B and 8C in order to detect the packet start code of the PES header. When detection signal is-pscp is output as shown in FIG. 8D, delay 15 in which flipflops are coupled at multi-stages delays it sequentially according to clock clk.

Meanwhile, stream ID code detector 14 searches the output of second flipflop 12 and detects the stream ID area of the PES header. Then, detection signal is-sid shown in FIG. 8E is output to detection signal generator 16. Detection signal generator 16 logically multiplies the outputs of delay 15 and stream ID code detector 14, and the flipflops hold the output of the AND gate according to clock clk so that PES header detection signal is-PES-header is output to copy prevention information extractor 20, as shown in FIG. 8P 8F.

Here, copy prevention information extractor 20 for detecting the copy prevention information is formed as shown in FIG. 9. When the parallel data output from PES header detector 10 and shown in FIG. 10A is held and output as shown in FIG. 10B, D-flipflop 22 synchronized to PES header detection signal is-PES-header of PES header detector 10 shown in FIG. 8F holds voltage +5V so that a HIGH signal is output to the clear ports of D-flipflops 23, 24 and 27 to release the clear states.

D-flipflops 23 is synchronized to the CR flag or the output of D-flipflop 21 shown in FIG. 10B to hold voltage Vcc so that a HIGH signal LCR is output as shown in FIG. 10C. D-flipflop 24 is synchronized to the OC flag of the output of D-flipflop 21 to hold voltage Vcc so that a HIGH signal LOC is output as shown in FIG. 10D.

Copy prevention position detector 25 searches the PD, TM and AC flags of the parallel data of PES header detector 10 shown in FIG. 10A to calculate the position of the additional copy information field, which is output to counter 26 as shown in FIG. 10E. Counter 26 receiving the 4-bit value performs counting so that a HIGH signal is output as shown in FIG. 10F at a predetermined counting value.

D-flipflop 27 synchronized to HIGH output rco of counter 26 holds the additional copy information field from the parallel data of D-flipflop 21 shown in FIG. 10B. The field is output as shown in FIG. 10C.

As described above, in the copy prevention method and apparatus for a digital video system of the present invention, a key information is recorded with a bit stream so that a VCR having the key information reproduces tape normally, thereby preventing illegal copy of tape. In addition, for key information transmission, the public-key encryption is introduced to disable a pirate to release the copy prevention, increasing reliability of copy prevention.

Claims

1. A copy prevention method for a digital video system comprising the steps of:

(a) receiving a digital data stream reproduced from a digital medium ;

(b) detecting an encryption key, which is a portion of said received digital data stream ;

(c) decrypting said encryption key using key information;

(d) decrypting digital video content included in said received digital data stream based on said decrypted encryption key; and

(e) transmitting said decrypted digital data stream video content to at least one of a monitor and a digital recorder reproducing device and a recording device.

2. A copy prevention method for a digital video system as claimed in claim 1, wherein said key information is predetermined by said digital video system.

3. A copy prevention method for a digital video system as claimed in claim 1, wherein said decrypting step (d) is operated in operates on units of a predetermined block of said received digital data stream .

4. A copy prevention apparatus for a digital video system comprising:

receiving means for receiving a a receiver to receive digital data stream reproduced from a digital medium ;

a key detector to detect an encryption key, which is a portion of said received digital data stream;

a decryption unit to decrypt said encryption key using key information and to decrypt digital video content included in said received digital data stream based on said decrypted encryption key; and

a controller to control transmission of said decrypted digital data stream video content to at least one of a monitor and a digital recorder reproducing device and a recording device.

5. A copy prevention apparatus for a digital video system as claimed in claim 4, wherein said key information is predetermined by said digital video system.

6. A copy prevention apparatus for a digital video system as claimed in claim 4, wherein said decryption unit is operated in operates on units of a predetermined block of said received digital data stream .

7. A copy prevention method for a digital video data system comprising the steps of:

(a) receiving a digital data stream reproduced from a digital medium ;

(b) detecting an encryption key, which is a portion of said received digital data stream ;

(c) decrypting said encryption key using key information; and

(d) decrypting digital content included in said received digital data stream based on said decrypted encryption key.

8. A copy prevention method for a digital video data system as claimed in claim 7, wherein said key information is predetermined by said digital video data system.

9. A copy prevention method for a digital video data system as claimed in claim 7, wherein said decrypting step (d) is operated in operates on units of a predetermined block of said received digital data stream.

10. A copy prevention apparatus for a digital video data system comprising:

receiving means for receiving a a receiver to receive digital data stream reproduced from a digital medium ;

a key detector to detect an encryption key, which is a portion of said received digital data stream; and

a decryption unit to decrypt said encryption key using key information and to decrypt digital content included in said received digital data stream based on said decrypted encryption key.

11. A copy prevention apparatus for a digital video data system as claimed in claim 10, wherein said key information is predetermined by said digital video data system.

12. A copy prevention apparatus for a digital video data system as claimed in claim 10, wherein said decryption unit is operated in operates on units of a predetermined block of said received digital data stream .

13. A copy prevention method for a digital video system comprising the steps of:

(a) receiving a digital data stream reproduced from a digital medium;

(b) detecting an encryption key, which is a portion of said received digital data stream ;

(c) decrypting said encryption key using predetermined key information;

(d) decrypting digital video content included in said received digital data stream based on said decrypted encryption key.

14. A copy prevention method for a digital video system as claimed in claim 13, wherein said decrypting step (d) is operated in operates on units of a predetermined block of said received digital data stream .

15. A copy prevention apparatus for a digital video system comprising:

a receiving means for receiving a unit to receive digital data stream reproduced from a digital medium;

a key detector to detect an encryption key, which is a portion of said received digital data stream ;

a decryption unit to decrypt said encryption key using predetermined key information and to decrypt digital video content included in said received digital data stream based on said decrypted encryption key.

16. A copy prevention apparatus for a digital video system as claimed in claim 15, wherein said decrypting unit is operated in operates on units of a predetermined block of said received digital data stream .

17. A copy prevention method for a digital data system, comprising the steps of:

(a) receiving first key information;

(b) encrypting second key information using said first key information;

(c) encrypting digital data streams using said second key information; and

(d) recording at least said encrypted second key information and said encrypted digital data streams on a digital medium.

18. The method of claim 17, wherein said step (b) randomly selects said second key information.

19. The method of claim 17, wherein said step (c) encrypts said digital data streams in blocks.

20. A copy prevention apparatus for a digital data system, comprising the steps of :

an encryption unit receiving first key information, encrypting second key information using said first key information, and encrypting digital data streams using said second key information; and

a controller controlling recording of at least said encrypted second key information and said encrypted digital data streams on a digital medium.

21. The apparatus of claim 20, wherein said encryption unit randomly selects said second key information.

22. The apparatus of claim 20, wherein said encryption unit encrypts said digital data streams in blocks.

23. A recording medium having a data structure for controlling operation of a copy prevention function in a digital data processing device, comprising:

a digital data area for storing digital data encrypted using first key information; and

a key information area for storing said first key information encrypted using second key information, said first key information operatively controlling the decryption of said encrypted digital data in a digital data process device.

24. A copy prevention method for a digital data system, comprising:

receiving first key information, said first key information for encrypting digital data;

encrypting said first key information using second information; and

transferring said encrypted first key information.

25. The method of claim 24, wherein said encrypting step involves a public key encrypts said second key information .

26. The method of claim 24, wherein said transferring step records said encrypted first key information on a digital medium.

27. The method of claim 24, wherein said transferring step transmits said encrypted first key information.

28. A copy prevention apparatus for a digital data system, comprising:

an encryption unit receiving first key information, said first key information for encrypting digital data, and encrypting said first key information using second key information; and

a controller controlling a transfer of said encrypted first key information.

29. The apparatus of claim 28, wherein said encryption unit uses a public key encrypts to encrypt said first key information.

30. The apparatus of claim 28, wherein said controller controls recording said encrypted first key information on a digital medium.

31. The apparatus of claim 28, wherein said controller controls transmitting said encrypted first key information.

32. The recording medium of claim 23, wherein the first key information is randomly selected.