Cryptography – Communication system using cryptography
Reexamination Certificate
1999-12-01
2004-12-21
Barrón, Gilberto (Department: 2132)
Cryptography
Communication system using cryptography
C380S259000, C380S281000, C380S284000, C713S171000
Reexamination Certificate
active
06834111
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a data transmitting/receiving method, a data transmission apparatus, a data reception apparatus, a data transmission/reception system, and a medium storing a program to direct a computer to perform all or a part of the function of means provided in each of the above described apparatuses.
In addition, the present invention relates to transmission of AV contents encrypted in different encrypting methods, and reception of the AV contents.
BACKGROUND ART
There are two conventional technologies, that is, a first conventional technology, and a second conventional technology, as described below.
First, the first conventional technology is described below. If data is to be provided only for a specific user, means, etc., then a method for preventing other users or means than the specific user or means from accessing the data is used by the transmission side encrypting and transmitting the data, and the reception side decrypting and uses the encrypted data.
The above described method is described below by referring to an example in which data is transmitted and received from an STB (Set Top Box, that is, a satellite broadcast receiver) for satellite broadcast to a VTR device for recording satellite broadcast data. In this method, data is encrypted to record correct satellite broadcast data only in the VTR device registered as a subscriber for recording satellite broadcast.
FIG. 14
shows a configuration of a conventional data transmission and reception system in which an STB for satellite broadcast functions as a data transmission device, and a VTR device functions as a data reception device. The configuration shows only the components relating to the transmission and reception of data between the STB and the VTR device, and reception means, etc. for receiving data from a satellite to the STB, and recording means, etc. for recording data to a recording medium in the VTR device are not shown here. The present system includes: an STB
101
for converting an electric wave received from a satellite into AV data and transmitting the data to a VTR device
102
; and the VTR device
102
for recording the AV data transmitted from the STB
101
in the recording medium.
The STB
101
includes: encryption means
111
for periodically or non-periodically updating a work key Kw, performing a first encryption process using the work key Kw on digital data D obtained by converting an electric wave received from a satellite into AV data so that the digital data D can be converted into encrypted digital data Kw (D), and transmitting the result to the VTR device
102
; a key encryption means
112
for generating a control key Kc, performing a second encryption process using the control key Kc on the work key Kw so that the work key Kw can be converted into an encrypted work key Kc (Kw), and transmitting the result to the VTR device
102
; a transmission side authentication and key exchange means
113
for performing an authentication and key exchange process with the VTR device
102
; and a D-I/F (digital interface)
114
for directly transmitting and receiving data to and from a D-I/F
124
of the VTR device
102
.
The VTR device
102
includes: the D-I/F
124
for directly transmitting and receiving data to and from the D-I/F
114
of the STB
101
; a reception side authentication and key exchange means
123
for performing an authentication and key exchange process with the transmission side authentication and key exchange means
113
of the STB
101
; key restoration means
122
for decrypting the encrypted work key Kc (Kw) using the control key Kc obtained through the reception side authentication and key exchange means
123
, and restoring the work key Kw; and decryption means
121
for decrypting the encrypted digital data Kw (D) using the work key Kw restored by the key restoration means
122
, and restoring the digital data D.
The data transmitted from the STB
101
to the VTR device
102
is the encrypted digital data Kw (D), the encrypted work key Kc (Kw), and the control key Kc. However, since the encrypted digital data Kw (D) and the encrypted work key Kc (Kw) are encrypted data, and the control key Kc is transmitted after the transmission side authentication and key exchange means
113
and the reception side authentication and key exchange means
123
perform an authentication process, the system has high security against the third party who is illegally using data.
Described below is the second conventional technology. As described above, in recent years there has been developed a technology for transmitting AV contents (AV data) such as movies, etc. using a digital signal, and receiving the AV contents.
A transmission device for transmitting such AV contents encrypts AV contents before transmission to protect the AV contents. A reception device receives and decrypts the encrypted AV contents, and displays the AV contents on the monitor.
As described above, the transmission device encrypts the AV contents. However, there are plural types of encrypting methods for encrypting the AV contents. For example, if the reception device is a normal domestic electric appliance such as a television, etc., then a “basic encrypting method” referred to as a baseline cipher such as M6, Blowfish, etc. is used corresponding to the domestic electric appliance. On the other hand, if, for example, the reception device is an appliance having a high-level arithmetic operations capability such as a personal computer, etc., then an “extended encrypting method” such as DES or the like which is more complicated and has a higher encryption level is used.
As in the conventional technology, the objects of the present invention exist corresponding to each of the first and second conventional technologies. Therefore, the objects are sequentially described below.
First, the object corresponding to the first conventional technology is described below. As described above, the control key Kc is transmitted after being authenticated. However, if the same control key Kc is continuously used, it may probably be decrypted by the third party. Therefore, the system can have higher security by periodically or non-periodically updating the control key Kc. However, since it is necessary to perform the authentication and key exchange process each time the control key Kc is updated, it is strongly demanded to minimize the frequency of the authentication and key exchange process for the purpose of reducing the load onto the system and improving the transmission and reception efficiency.
FIG. 15
shows a relationship between the execution of the control key update process and the authentication and that of key exchange process when the control key is updated by the conventional data transmission and reception system. The horizontal axis indicates the passage of time. The bar in the first row indicates that the STB is transmitting a data signal. The arrow in the second row indicates the range in which the same control key Kc is used.
FIG. 15
shows that control key Kc [
1
] is updated into control key Kc [
2
]. The bars in the third through fifth rows indicate that the VTR device is in a reception state. The ranges in which the bars are broken indicate that the reception is suspended. The two vertical arrows in the third through fifth rows indicate that the authentication and key exchange process has been performed.
Since the VTR device in case
1
is not suspended after starting the reception, it performs the authentication and key exchange process after starting the reception, and afterwards performs the authentication and key exchange process only when the control key Kc is updated. Since the VTR device in cases
2
and
3
is suspended after starting the reception, it is required to perform the authentication and key exchange process when resuming the reception. Especially, although the VTR device in case
3
is suspended only for a short time without update of the control key Kc when the reception is resumed, the authentication and key exchange process is to be p
Gotoh Shoichi
Iitsuka Hiroyuki
Nishimura Takuya
Takechi Hideaki
Yamada Masazumi
Barrón Gilberto
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
Zand Kambiz
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