Cryptography – Video cryptography – Copy protection or prevention
Reexamination Certificate
1998-10-29
2002-10-08
Smithers, Matthew (Department: 2132)
Cryptography
Video cryptography
Copy protection or prevention
C705S057000
Reexamination Certificate
active
06463151
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a data transmission method, a data receiving method, a data transmission system, and a program recording medium used for transmitting and receiving, for example, digital data.
2. Description of the Related Art
Conventional data transfer method includes one employing IEEE 1394 Standard (IEEE: The Institute of Electrical and Electronic Engineers, Inc.) (reference: IEEE 1394 High Performance Serial Bus). Data transfer in IEEE 1394 Standard includes isochronous communication suitable for transfer of isochronous data such as video or sound signals, and asynchronous communication suitable for transfer of asynchronous data such as control signals, and both communications can simultaneously exist on an IEEE 1394 bus.
The isochronous communication is so-called broadcasting type communication. Isochronous packets output from a device on the IEEE 1394 bus can be received by all other devices on the bus.
On the other hand, the asynchronous communication includes peer-to-peer communication and a broadcasting type communication. Then, an asynchronous packet output from a device on the bus contains an identifier identifying a device receiving that packet. If the identifier indicates a specific device, the device specified by the identifier receives the asynchronous packet, and, if the identifier indicates broadcast, all devices on the bus receive the asynchronous packet.
In addition, IEC (International Electrotechnical Commission) is studying IEC 61883 Standard (hereinafter called an “AV protocol”) as a standard for transferring a digital audio or video signal employing IEEE 1394 Standard, or managing connections of a data transmission path between equipment attached on the IEEE 1394 bus. In the AV protocol, video/audio data is arranged and transmitted in an isochronous packet. In addition, an isochronous packet contains a CIP (Common Isochronous Packet) header. The CIP header contains identification information indicating a type of video/audio data, and information such as a device number of source device transmitting an isochronous packet.
For a data transmission system employing such conventional data transfer method, a data transmission system is proposed to limit the number of copies of data to be transferred with data protection information in view of protection of copyright of data to be transmitted. Digital data requiring such copy limiting mechanism includes video data which is digitized video images, audio data which is digitized sound, and digital data which is a combination of them.
Now, such conventional data transmission system is described for its arrangement with reference to FIG.
6
.
FIG. 6
is a format of isochronous packet used in the conventional data transmission system.
As shown in the figure, the isochronous packet
101
comprises an isochronous packet header
900
, a header CRC
901
, an isochronous payload
902
, and data CRC
903
.
The isochronous packet header
900
contains an Sy field
910
for storing data protection information. If the value stored in the most significant two bits of the Sy field
910
is 00, it indicates that data to be transmitted (real data
905
described later) is data freely copied. If it is 10, it indicates that the data can be copied only once, while, if it is
11
, it indicates that the data is copy prohibited.
In addition, the isochronous packet header
900
contains a two-bit tag
907
. If the tag
907
has a value of 01, it indicates that the isochronous packet is an isochronous packet conforming to the AV protocol. When the tag
907
has a value of 01, that is, when the isochronous packet is an isochronous packet conforming to the AV protocol, a CIP header
904
is contained at the top of an isochronous payload
902
.
The CIP header
904
contains a source ID
906
which is an identifier of the device outputting the isochronous packet. The CIP header
904
also contains FMT
908
or FDF
909
. indicating what type data the real data
905
contained in the isochronous payload
902
is.
Data such as video or audio to be transmitted is contained in the real data
905
. The real data
905
is encrypted data if the data protection information is 10 or 11, and not encrypted if it is 00 indicating copy-freely. The data protection information is also contained in the real data
905
, and generally called SCMS for CD and CGMS for DV.
Now, operation is described for such arrangement.
When a source device transmits digital data, it embeds data protection information indicating a condition whether or not the data can be copied in the Sy field
910
in the isochronous packet header
900
, and transmits the information together with the real data
905
. A sink device retrieves the data protection information from the Sy field
910
in the received data, and changes over the operation of equipment in recording the digital data based on the result of interpretation on the data protection information. In addition, except for a case where it is copy-freely data, since the real data is encrypted, the sink device sends a transfer request for decryption information necessary for decrypting it to the source device. Upon receipt of the request, the source device sends decryption information to the requesting device. The sink device decrypts the received real data
905
using the decryption information sent from the source device. The real data
905
thus decrypted is displayed on a display device. On the other hand, an operation for recording the decrypted real data is appropriately changed over based on content of the data protection information.
That is, when the sink device is, for example, a VTR, and the retrieved data protection information means “copy-one-generation”, the decrypted data is recorded on video tape loaded in the VTR. If it means “copy-prohibited”, the recording operation is not performed even if a recording button has been pressed.
However, in such conventional data transmission system, there is a problem that, if the data protection information contained in the Sy field
910
is tampered on a transmission path between the source device and the sink device by a person intending to conduct an unauthorized action, the decrypted data is unauthorizedly copied.
That is, for example, it is assumed that, when the data protection information contained in the Sy field
910
of the isochronous packet header
900
has a value of 11 indicating “copy-prohibited” in the stage when the data is transmitted from the source device, a person conducting an illegal action tampers the value of data protection information to 10 indicating “copy-one-generation” on the transmission path. This case is described in detail in the following.
In this case, the VTR at the sink device checks the data protection information contained in the Sy field
910
, and detects that its value is 10. In this case, since the real data
905
is encrypted as described above, the sink device sends a transmission request for decryption information for decrypting it to the source device. Upon receipt of the request, the source device sends the decryption information to the sink device. The sink device decrypts the real data
905
using the decryption information being sent, and then displays the decrypted real data on the display device or the like. Then, there arises a problem that, since the VTR has detected the fact that the data protection information contained in the Sy field
910
has a value of
10
, it determines that the received real data
905
is copy-one-generation although it is originally copy-prohibited data, and records the decrypted real data on the video tape.
SUMMARY OF THE INVENTION
The present invention is intended to provide a data transmission method, a data receiving method, a data transmission system, and a program recording medium in which transmission data can be more surely protected than in the prior art by taking into account such problems in the conventional data transmission system.
The 1st aspect of the present invention is a data transmission method comprising th
Iitsuka Hiroyuki
Matsuzaki Natsume
Takechi Hideaki
Yamada Masazumi
Matsushita Electric - Industrial Co., Ltd.
Ratner & Prestia
Smithers Matthew
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