Cryptography – Key management – Having particular key generator
Reissue Patent
2000-02-23
2003-08-26
Cangialosi, Salvatore (Department: 2661)
Cryptography
Key management
Having particular key generator
C380S047000
Reissue Patent
active
RE038236
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a digital signal transmitting method, a digital signal receiving apparatus, and a recording medium, and is applicable, for example, to a digital signal transmitting system which provides fee-charged software information to contract users.
2. Description of the Related Art
In a conventional digital signal transmitting system using satellites or cables, as shown in
FIG. 1
, a program source PS, input to a digital signal transmitting apparatus, i.e., a broadcasting station
1
, is band-compression coded with a moving picture image coding experts group (MPEG) method by means of an MPEG encoder
2
and is converted to packet transmission data by means of a packet generation section
3
.
The packetized transmission data is multiplexed by a multiplexer
4
, then the transmission data is scrambled for security by an encryption processing section
5
, and finally keys (ciphers) are put over the scrambled data many times so that the scrambling cannot be descrambled easily. The encrypted transmission data is error corrected by a forward error correction (FEC) section
6
and modulated by a modulator
7
. The modulated data is then sent through a digital satellite
8
directly to a digital signal receiving apparatus installed in a contract user's household, i.e., a terminal
10
(FIG.
2
), or sent through the digital satellite
8
to a signal distributing station
9
(
FIG. 2
) which is called a head end. The data, transmitted to the signal distributing station
9
, is sent to the terminal
10
via cable.
Now, as shown in
FIG. 2
, in the terminal
10
, when the transmission data is directly sent via the satellite
8
, the data is received by an antenna
11
and sent to a front end section
12
. When the transmission data is sent from the signal distributing station
9
via the cable, it is inputted directly to the front end section
12
. A user contracting with the broadcasting station
1
accesses a key authorized to each user to the terminal
10
, with respect to the transmission data sent directly from the satellite
8
or from the satellite
8
via the signal distributing station
9
, so that the user is authorized as a contract user and bill processing is performed, and at the same time, the user can appreciate desired software information.
That is, in the terminal
10
, the transmission data is processed by the front end section
12
comprising a tuner, a demodulator, and an error corrector, and the processed data is input to a data fetch section
13
. In the data fetch section
13
, the multiplexed data is demultiplexed by the demultiplexer
14
so that the data is separated into a video signal, an audio signal, and data other than these signals. In a decryption section
15
, ciphers are decrypted while performing bill processing. In a packet separation section
16
, the decrypted data is packet separated. Finally, the compression of the data is expanded by an MPEG decoder
17
, and the video and audio signals, which are digital-to-analog converted to analog signals, are output to television.
Incidentally, in the digital signal transmission system, when fee-charged software information such as video on demand or near video on demand is transmitted, a digital storage
18
such as tape media or disk media is incorporated into or connected to the terminal
10
to meet the convenience of users and to effectively utilize a digital transmission path. In such a case, large amounts of software data have been downloaded to the storage
18
by making use of an unoccupied time band and an unoccupied transmission path, and when the user looks at the software information at hand, the user accesses it with an ID card (for example, smart card)
19
to perform bill processing, and reproduction limitation is lifted.
More specifically, if the user accesses a central processing unit (CPU)
20
by means of the smart card
19
, the CPU
20
performs an inquiry of registration to an authorization center
22
(
FIG. 1
) through a modem
21
. The authorization center
22
confirms registration by means of a conditional access
23
. If registration is confirmed, the authorization center
22
performs bill processing and also performs notification of confirmation to the CPU
20
through the modem
21
.
The CPU
20
instructs decryption of key to a local conditional access
24
by this notification, and the local conditional access
24
decrypts a cipher which has been put over the data recorded on the storage
18
. Hence, the reproduction limitation is lifted, and the packet of the data recorded on the storage
18
is separated by the packet separation section
16
. The compression of the packet-separated data is decompressed (expanded) by the MPEG decoder
17
and then the expanded data is digital-to-analog converted to be output to television as the analog signal and audio signal A/V.
However, if, in the security system in a current broadcasting form, software information has been downloaded to the storage
18
, as described above, to try to realize a system where this software can be appreciated when user wants to see it, then the following problems will arise.
More specifically, in the current digital signal transmitting system, when a cipher is decrypted by the decrypting section
15
and then software information is downloaded to the storage
18
, as shown by point A in
FIG. 3
, fee-charged software cannot be downloaded to the storage
18
by decrypting the cipher without billing, because decrypting a cipher is, vis-a-vis, billing. Now, if only billing information is made free, all ciphers of data are decrypted, and downloaded to the storage
18
, then a piece of software information is passed as it is and output from the terminal
10
.
Also, in a case where the storage
18
is not incorporated into the terminal
10
but is connected to the terminal
10
and switching means is not provided between the decryption section
15
and the packet separation section
16
, if ciphers are all decrypted and downloaded to the storage
18
, then the decrypted data are all sent and there is the possibility that they can been seen for free at point C of
FIG. 3
by persons other than contract users.
To solve these problems, data can be downloaded to the storage
18
before ciphers are decrypted, i.e., after multiplex is demultiplexed by the demultiplexer
14
(point B of FIG.
3
). If, however, data are downloaded to the storage
18
after multiplex is demultiplexed by the demultiplexer
14
, there is the problem that intra-coded (I) pictures can not be pulled out and can not be reproduced at variable speed, because data remain encrypted. Also, in broadcasting systems where data are encrypted, keys are changed annually or biennially to ensure security. Therefore, when a key is changed after software information is downloaded to the storage
18
, there is the problem that ciphers cannot be decrypted and therefore the downloaded software information cannot be seen.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of this invention is to provide a digital signal transmitting method, a digital signal receiving apparatus, and a recording medium which are capable of ensuring security when fee-charged software information is transmitted.
The foregoing object and other objects of the invention have been achieved by the provision of a digital signal transmitting method where at least a band-compression coded digital video signal is given encryption processing and transmitted, in which when an image providing predetermined services is transmitted, the band-compression coded digital signal is given first-encryption processing and then the first-encryption processed digital signal is further given the encryption processing and transmitted.
Also, according to the present invention, in the digital signal transmitting method where at least a band-compression coded digital video signal is given encryption processing and transmitted, the band-compression coded and encryption processed digital signal is mixed with the digital signal
Goto Koichi
Kubota Yukio
Cangialosi Salvatore
Frommer Williams S.
Kessler Gordon
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