U.S. patent application number 09/915913 was filed with the patent office on 2002-01-10 for data control method, method for embedding data control information, method for detecting data control information, device for embedding data control information, device for detecting data control information, and device for recording data.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Ibaraki, Susumu, Katta, Noboru.
Application Number | 20020003879 09/915913 |
Document ID | / |
Family ID | 16101134 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003879 |
Kind Code |
A1 |
Ibaraki, Susumu ; et
al. |
January 10, 2002 |
Data control method, method for embedding data control information,
method for detecting data control information, device for embedding
data control information, device for detecting data control
information, and device for recording data
Abstract
A data control method includes the steps of: A) at least one of
the following steps: A-1) embedding prohibition information in
data, wherein copying of the data is to be prohibited; and A-2)
embedding the prohibition information and N pieces of permission
information in the data (N is a natural number), wherein the
copying of the data is to be permitted N times; and B) detecting
the prohibition and/or permission information prior to the copying
of the data. In the case where the permission information is
detected from the data prior to the copying of the data, at least
one of the N pieces of permission information in the data is
invalidated, and then the copying of the data is permitted. In the
case where the permission information is not detected from the
data, and the prohibition information is detected from the data
prior to the copying of the data, the copying of the data is
prohibited.
Inventors: |
Ibaraki, Susumu; (Osaka,
JP) ; Katta, Noboru; (Itami-shi, JP) |
Correspondence
Address: |
Mark D. Saralino
RENNER, OTTO, BOISSELLE & SKLAR, P.L.L.
Nineteeth Floor
1621 Euclid Avenue
Cleveland
OH
44115-2191
US
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd.
|
Family ID: |
16101134 |
Appl. No.: |
09/915913 |
Filed: |
July 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09915913 |
Jul 25, 2001 |
|
|
|
09110560 |
Jul 6, 1998 |
|
|
|
Current U.S.
Class: |
380/201 ;
713/176; G9B/20.002 |
Current CPC
Class: |
G11B 20/00768 20130101;
G06T 1/0021 20130101; G06T 1/0071 20130101; G11B 20/00086 20130101;
G11B 20/00173 20130101; G11B 20/00746 20130101; G11B 20/00123
20130101; G06T 2201/0064 20130101 |
Class at
Publication: |
380/201 ;
713/176 |
International
Class: |
H04L 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 7, 1997 |
JP |
9-181459 |
Claims
What is claimed is:
1. A data control method comprising the steps of: A) at least one
of the following steps: A-1) embedding prohibition information in
data, wherein copying of the data is to be prohibited; and A-2)
embedding the prohibition information and N pieces of permission
information in the data (N is a natural number), wherein the
copying of the data is to be permitted N times; and B) detecting
the prohibition and/or permission information prior to the copying
of the data, wherein in the case where the permission information
is detected from the data prior to the copying of the data, at
least one of the N pieces of permission information in the data is
invalidated, and then the copying of the data is permitted, and
wherein in the case where the permission information is not
detected from the data, and the prohibition information is detected
from the data prior to the copying of the data, the copying of the
data is prohibited.
2. A data control method according to claim 1, wherein the
permission information is a digital signature f(M); and the digital
signature f(M) is derived based on a digital code M which is
extracted from the data.
3. A method for embedding data control information comprising one
of the following steps: embedding prohibition information in data,
wherein copying of the data is to be prohibited; and embedding the
prohibition information and N pieces of permission information in
the data (N is a natural number), wherein the copying of the data
is to be permitted N times.
4. A method for embedding data control information according to
claim 3, wherein the permission information is a digital signature
f(M) for a digital code M which is uniquely derived from the
data.
5. A method for detecting data control information comprising the
step of: detecting predetermined permission and/or prohibition
information prior to copying of data, wherein in the case where the
predetermined permission information is detected from the data
prior to the copying of the data, the predetermined permission
information is invalidated, and then the copying of the data is
permitted, and wherein in the case where the predetermined
permission information is not detected from the data, and the
predetermined prohibition information is detected from the data
prior to the copying of the data, the copying of the data is
prohibited.
6. A method for detecting data control information comprising the
step of: authenticating a digital signature f(M) in data based on a
digital code M which is derived from data, wherein in the case
where the digital signature f(M) in the data is authenticated prior
to copying of the data, the copying of the data is permitted, and
wherein in the case where the digital signature f(M) in the data is
not authenticated prior to the copying of the data, the copying of
the data is prohibited.
7. A device for embedding data control information, comprising: a
section for embedding prohibition information, which embeds
prohibition information indicating at least a prohibition against
copying of data in the data; and a section for embedding permission
information, which embeds N pieces of permission information in the
data along with the embedding of the prohibition information by the
section for embedding prohibition information in the case where the
copying of the data is to be permitted N times, wherein N is a
natural number.
8. A device for embedding data control information according to
claim 7, wherein the section for embedding permission information
has a code extracting section for extracting a digital code M from
the data.
9. A device for embedding data control information according to
claim 8, wherein the section for embedding permission information
includes: a signature section for generating a digital signature
f(M) based on the digital code M which is extracted by the code
extracting section and a first public key held by a producer of the
data; and a signature embedding section for embedding the digital
signature f(M) generated by the signature section in the data as
the permission information.
10. A device for detecting data control information which extracts
prohibition information and permission information embedded in
data, comprising: a permission information detecting section for
detecting the permission information from the data; a permission
information invalidating section for invalidating the permission
information in the data; a prohibition information detecting
section for detecting the prohibition information from the data;
and a determining section which sets a copy permission/prohibition
flag to be in a copy permissive state and then outputs the flag in
the case where the permission information is detected by the
permission information detecting section; and sets the copy
permission/prohibition flag to be in a copy prohibited state and
then outputs the flag in the case where the permission information
is not detected by the permission information detecting section,
and the prohibition information is detected by the prohibition
information detecting section.
11. A device for detecting data control information according to
claim 10, wherein the permission information detecting section has
a code extracting section for extracting a digital code M from the
data.
12. A device for detecting data control information according to
claim 11, wherein the permission information detecting section
includes: a signature extracting section for extracting a digital
signature f(M) which is embedded in the data; and an authentication
section which generates a digital signature f(M) based on the
digital code M extracted by the code extracting section and a
second public key, compares the generated digital signature f(M)
with the digital signature f(M) extracted by the signature
extracting section, and validates a copy permission flag and
outputs the flag if the digital signature f(M) is
authenticated.
13. A device for recording data on a recording medium, comprising:
a permission information detecting section for detecting the
permission information from the data; a permission information
invalidating section for invalidating the permission information in
the data; a prohibition information detecting section for detecting
the prohibition information from the data; and a determining
section which sets a copy permission/prohibition flag to be in a
copy permissive state and then outputs the flag in the case where
the permission information is detected by the permission
information detecting section; and sets the copy
permission/prohibition flag to be in a copy prohibited state and
then outputs the flag in the case where the permission information
is not detected by the permission information detecting section,
and the prohibition information is detected by the prohibition
information detecting section; and a data recording section which
records the data in the case where the copy permission/prohibition
flag is set to be in the copy permissive state by the determining
section, and does not record the data in the case where the copy
permission/prohibition flag is set to be in the copy prohibited
state by the determining section.
14. A device for recording data according to claim 13, wherein the
permission information detecting section has a code extracting
section for extracting a digital code M from the data.
15. A data control method comprising the steps of: A) at least one
of the following steps: A-1) embedding prohibition information in
data, wherein processing of the data is to be prohibited; and A-2)
embedding the prohibition information and N pieces of permission
information in the data (N is a natural number), wherein the
processing of the data is to be permitted N times; and B) detecting
the permission and/or prohibition information prior to the
processing of the data, wherein in the case where the permission
information is detected from the data prior to the processing of
the data, at least one of the N pieces of permission information in
the data is invalidated, and then the processing of the data is
permitted, and wherein in the case where the permission information
is not detected from the data, and the prohibition information is
detected prior to the processing of the data, the processing of the
data is prohibited.
16. A method for embedding data control information comprising one
of the following steps of: embedding prohibition information in
data, wherein processing of the data is to be prohibited; and
embedding the prohibition information and N pieces of permission
information in the data (N is a natural number), wherein the
processing of the data is to be permitted N times.
17. A method for detecting data control information comprising the
following step of: detecting predetermined permission and/or
prohibition information prior to processing of data, wherein in the
case where the predetermined permission information is detected
from the data prior to the processing of the data, the
predetermined permission information is invalidated so as to permit
the processing of the data, and wherein in the case where the
predetermined permission information is not detected from the data,
and the predetermined prohibition information is detected from the
data prior to the processing of the data, the processing of the
data is prohibited.
18. A device for embedding data control information, comprising: a
section for embedding prohibition information, which embeds
prohibition information indicating prohibition against processing
of data in the data; and a section for embedding permission
information, which embeds N pieces of permission information in the
data along with the embedding of the prohibition information by the
section for embedding prohibition information in the case where the
processing of the data is to be permitted N times, wherein N is a
natural number.
19. A device for detecting data control information which extracts
prohibition information and permission information embedded in
data, comprising: a permission information detecting and deleting
section which, in the case where N pieces of permission information
(N is a natural number) are detected from the data, invalidates at
least one of the N pieces of permission information in the data,
validates a permission flag, and outputs the flag; a prohibition
information detecting section which validates a prohibition flag
and outputs the flag in the case where the prohibition information
is detected from the data; and a determining section which sets a
permission/prohibition flag to be in a permissive state and then
outputs the flag when the permission flag is valid or the
prohibition flag is not valid, and sets the permission/prohibition
flag to be in a prohibited state and then outputs the flag when the
permission flag is invalid and the prohibition information is
valid.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for embedding data
control information for controlling the permission or prohibition
to copy recorded data in order to prevent data whose copyright
should be protected (e.g., an audio software, a graphic software,
or the like) from being copied or processed (i.e., manipulated),
and a device for realizing the method; a method for detecting such
data control information, and a device for realizing the method;
and a data control method in which the method for embedding data
control information and the method for detecting data control
information are combined.
[0003] 2. Description of the Related Art
[0004] As a method for embedding copy control information in an
image, or as a method for detecting copy control information, a
method referred to as Patchwork is known. This method is described
in "Data hiding techniques for supporting water mark (I)", Nikkei
Electronics, No. 683, pp. 149-162, published in Feb. 24, 1997 (this
is a translation of "Techniques for data hiding" by W. Bender, D.
Gruhl, N. Morimoto, and A. Lu, IBM Systems Journal, Vol 35, NOS 3
& 4, 1996). Hereinafter, a conventional method for embedding
copy control information and a conventional method for detecting
such a copy control information will be described.
[0005] As the conventional method for embedding copy control
information, a process for embedding a copy permission/prohibition
bit (one bit) in an image will be described hereinafter. When
copying is permitted, the copy permission/prohibition bit is set to
be 1. When copying is prohibited, the copy permission/prohibition
bit is set to be 0. Two points (i.e., Ai and Bi) are selected from
the image by means of pseudo random numbers. Next, when a bit to be
embedded is 1, the brightness level of Ai, i.e., Yai, is raised by
an amount d, and the brightness level of Bi, i.e., Ybi, is lowered
by the amount d. Conversely, when a bit to be embedded is 0, the
brightness level of Ai is lowered by the amount d, and the
brightness level of Bi is raised by the amount d. The value of d is
an integer from 1 to 5. Such processing is repeated n times (n is
generally about 10,000).
[0006] Next, the conventional method for detecting copy control
information will be described. First, brightness levels (i.e. pixel
information) at the same two points as those selected at the time
of embedding information (i.e., (Yai+d, Ybi-d) or (Yai-d, Ybi+d))
are extracted from the image by pseudo random numbers. Next, the
difference between these two points is calculated. These processing
steps are repeated n times, and a mean value of the thus-obtained
differences is calculated. If the mean value is equal to or greater
than d, the embedded bit is considered to be 1, and if the mean
value is equal to or less than -d, the embedded bit is considered
to be 0. If the mean value is between -d and d, it is considered
that no information is embedded.
[0007] Herein, the expected value of (Yai-Ybi) is estimated to be
0. The expected value of (Yai+d)-(Ybi-d) is 2d, and the expected
value of (Yai-d)-(Ybi+d) is -2d. Accordingly, determination is
performed assuming that the threshold values of displacement from
the mean value of 0 are d and -d. In order to perform more accurate
determination, copy control information can be detected by finding
the statistical distribution of such differences, and measuring the
displacement of its variance from the estimated value.
[0008] As described above, according to the conventional method for
embedding copy control information and the conventional method for
detecting copy control information, it is possible to embed and
detect a one-bit copy permission/prohibition flag. According to
another method, a constant level d is not added or subtracted in
the selected pixels. Rather, information is embedded as follows.
The level of embedding is changed for each of the pixels in
accordance with the characteristics of its image, and such a level
is respectively added to, or subtracted from, the brightness of
each of the pixels so that the mean of such calculations becomes
level d. As a result, it is possible to suppress the deterioration
of the image after embedding the information and to make it more
difficult to conduct tampering.
[0009] Therefore, the method for embedding copy control information
and the method for detecting the copy control information are
required not only to indicate the permission or prohibition to copy
but also to control the number of allowed copies (e.g., to control
the number of copies so as to limit the number of copies made to
N). In order to control the number of copies, it is necessary to
rewrite copy control information upon copying. For example, in the
case of a software whose copying is permitted only once, the copy
control information indicating that copying is permitted once is
embedded in the software. Upon copying the software, the copy
control information must be replaced by new copy control
information indicating copying is prohibited.
[0010] In order to realize such rewriting of copy control
information by the conventional method for embedding copy control
information and the conventional method for detecting the copy
control information, both of these methods must be executed when a
user makes a copy. Since the conventional method for embedding copy
control information is hard to process as compared to the method
for detecting the copy control information, its realization by a
user leads to an increase in cost. In addition, since the method
for embedding copy control information is disclosed to the user,
there exists a possibility that tempering can be carried out rather
easily.
SUMMARY OF THE INVENTION
[0011] According to one aspect of this invention, a data control
method includes the steps of: A) at least one of the following
steps: A-1) embedding prohibition information in data, wherein
copying of the data is to be prohibited; and A-2) embedding the
prohibition information and N pieces of permission information in
the data (N is a natural number), wherein the copying of the data
is to be permitted N times; and B) detecting the prohibition and/or
permission information prior to the copying of the data. In the
case where the permission information is detected from the data
prior to the copying of the data, at least one of the N pieces of
permission information in the data is invalidated, and then the
copying of the data is permitted. In the case where the permission
information is not detected from the data, and the prohibition
information is detected from the data prior to the copying of the
data, the copying of the data is prohibited.
[0012] In one embodiment of the present invention, the permission
information is a digital signature f(M); and the digital signature
f(M) is derived based on a digital code M which is extracted from
the data.
[0013] According to another aspect of this invention, a method for
embedding data control information includes one of the following
steps of: embedding prohibition information in data, wherein
copying of the data is to be prohibited; and embedding the
prohibition information and N pieces of permission information in
the data in the data (N is a natural number), wherein the copying
of the data is to be permitted N times.
[0014] In one embodiment of the present invention, the permission
information is a digital signature f(M) for a digital code M which
is uniquely derived from the data.
[0015] According to still another aspect of this invention, a
method for detecting data control information includes the step of
detecting predetermined permission and/or prohibition information
prior to copying of data. In the case where the predetermined
permission information is detected from the data prior to the
copying of the data, the predetermined permission information is
invalidated so as to permit the copying of the data. In the case
where the predetermined permission information is not detected from
the data, and the predetermined prohibition information is detected
from the data prior to the copying of the data, the copying of the
data is prohibited.
[0016] According to still yet another aspect of this invention, a
method for detecting data control information includes the step of
authenticating a digital signature f(M) in data based on a digital
code M which is derived from data. In the case where the digital
signature f(M) in the data is authenticated prior to copying of the
data, the copying of the data is permitted. In the case where the
digital signature f(M) in the data is not authenticated prior to
the copying of the data, the copying of the data is prohibited.
[0017] According to still yet another aspect of this invention, a
device for embedding data control information includes: a section
for embedding prohibition information, which embeds prohibition
information indicating at least a prohibition against copying of
data in the data; and a section for embedding permission
information, which embeds N pieces of permission information in the
data along with the embedding of the prohibition information by the
section for embedding prohibition information in the case where the
copying of the data is to be permitted N times, wherein N is a
natural number.
[0018] In one embodiment of the present invention, the section for
embedding permission information has a code extracting section for
extracting a digital code M from the data.
[0019] In another embodiment of the present invention, the section
for embedding permission information includes: a signature section
for generating a digital signature f(M) based on the digital code M
which is extracted by the code extracting section and a first
public key held by a producer of the data; and a signature
embedding section for embedding the digital signature f(M)
generated by the signature section in the data as the permission
information.
[0020] According to still yet another aspect of this invention, a
device for detecting data control information which extracts
prohibition information and permission information embedded in data
includes: a permission information detecting section for detecting
the permission information from the data; a permission information
invalidating section for invalidating the permission information in
the data; a prohibition information detecting section for detecting
the prohibition information from the data; and a determining
section which sets a copy permission/prohibition flag to be in a
copy permissive state and then outputs the flag in the case where
the permission information is detected by the permissive
information detecting section, and sets the copy
permission/prohibition flag to be in a copy prohibited state and
then outputs the flag in the case where the permission information
is not detected by the permission information detecting section,
and the prohibition information is detected by the prohibition
information detecting section.
[0021] In one embodiment of the present invention, the permission
information detecting section has a code extracting section for
extracting a digital code M from the data.
[0022] In another embodiment of the present invention, the
permission information detecting section includes: a signature
extracting section for extracting a digital signature f(M) which is
embedded in the data; and an authentication section which generates
a digital signature f(M) based on the digital code M extracted by
the code extracting section and a second public key, compares the
generated digital signature f(M) with the digital signature f(M)
extracted by the signature extracting section, and validates a copy
permission flag and outputs the flag if the digital signature f(M)
is authenticated.
[0023] According to still yet another aspect of this invention, a
device for recording data on a recording medium includes: a
permission information detecting section for detecting the
permission information from the data; a permission information
invalidating section for invalidating the permission information in
the data; a prohibition information detecting section for detecting
the prohibition information from the data; and a determining
section which sets a copy permission/prohibition flag to be in a
copy permissive state and then outputs the flag in the case where
the permission information is detected by the permission
information detecting section, and sets the copy
permission/prohibition flag to be in a copy prohibited state and
then outputs the flag in the case where the permission information
is not detected by the permission information detecting section,
and the prohibition information is detected by the prohibition
information detecting section; and a data recording section which
records the data in the case where the copy permission/prohibition
flag is set to be in the copy permissive state by the determining
section, and does not record the data in the case where the copy
permission/prohibition flag is set to be in the copy prohibited
state by the determining section.
[0024] In one embodiment of the present invention, the permission
information detecting section has a code extracting section for
extracting a digital code M from the data.
[0025] According to still yet another aspect of this invention, a
data control method includes the steps of: A) at least one of the
following steps: A-1) embedding prohibition information in data,
wherein processing of the data is to be prohibited; and A-2)
embedding the prohibition information and N pieces of permission
information in the data (N is a natural number), wherein the
processing of the data is to be permitted N times; and B) detecting
the permission and/or prohibition information prior to the
processing of the data. In the case where the permission
information is detected from the data prior to the processing of
the data, at least one of the N pieces of permission information in
the data is invalidated, and then the processing of the data is
permitted. In the case where the permission information is not
detected from the data, and the prohibition information is detected
prior to the processing of the data, the processing of the data is
prohibited.
[0026] According to still yet another aspect of this invention, a
method for embedding data control information includes one of the
following steps of: embedding prohibition information in data,
wherein processing of the data is to be prohibited; and embedding
the prohibition information and N pieces of permission information
in the data (N is a natural number), wherein the processing of the
data is to be permitted N times.
[0027] According to still yet another aspect of this invention, a
method for detecting data control information includes the
following step of: detecting predetermined permission and/or
prohibition information prior to processing of data. In the case
where the predetermined permission information is detected from the
data prior to the processing of the data, the predetermined
permission information is invalidated so as to permit the
processing of the data. In the case where the predetermined
permission information is not detected from the data, and the
predetermined prohibition information is detected from the data
prior to the processing of the data, the processing of the data is
prohibited.
[0028] According to still yet another aspect of this invention, a
device for embedding data control information includes: a section
for embedding prohibition information, which embeds prohibition
information indicating prohibition against processing of data in
the data; and a section for embedding permission information, which
embeds N pieces of permission information in the data along with
the embedding of the prohibition information by the section for
embedding prohibition information in the case where the processing
of the data is to be permitted N times, wherein N is a natural
number.
[0029] According to still yet another aspect of this invention, a
device for detecting data control information which extracts
prohibition information and permission information embedded in data
includes: a permission information detecting and deleting section
which, in the case where N pieces of permission information (N is a
natural number) are detected from the data, invalidates at least
one of the N pieces of permission information in the data,
validates a permission flag, and outputs the flag; a prohibition
information detecting section which validates a prohibition flag
and outputs the flag in the case where the prohibition information
is detected from the data; and a determining section which sets a
permission/prohibition flag to be in a permissive state and then
outputs the flag when the permission flag is valid or the
prohibition flag is not valid, and sets the permission/prohibition
flag to be in a prohibited state and then outputs the flag when the
permission flag is invalid and the prohibition information is
valid.
[0030] Thus, the invention described herein makes possible the
advantages of providing a method for embedding data control
information which can control not only the permission or
prohibition to copy, but also control the number of copies, and
which makes it more difficult to conduct tampering, and a device
for realizing the same; a method for detecting the data control
information, and a device for realizing such a method; a method for
embedding data control information which limits manipulation of
data or data processing of displayed contents or the like, and a
device for realizing such a method; and a method for detecting the
data control information, and a device for realizing such a
method.
[0031] These and other advantages of the present invention will
become apparent to those skilled in the art upon reading and
understanding the following detailed description with reference to
the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIGS. 1A to 1D are views for describing the summary of a
data control method according to Embodiment 1 of the present
invention;
[0033] FIG. 2 is a flow chart showing a method for embedding data
control information according to Embodiment 1 of the present
invention;
[0034] FIG. 3 is a flow chart showing a process in the method for
embedding data control information shown in FIG. 2;
[0035] FIG. 4 is a flow chart showing a method for detecting data
control information according to Embodiment 1 of the present
invention;
[0036] FIG. 5 is a flow chart showing a process in the method for
detecting data control information shown in FIG. 4;
[0037] FIG. 6 is a view for illustrating the structure of a data
control system according to Embodiment 2 of the present
invention;
[0038] FIG. 7 is a view for illustrating the structure of a method
for embedding permission information in the data control system
shown in FIG. 6; and
[0039] FIG. 8 is a view for illustrating the structure of a method
for detecting the permission information in the data control system
shown in FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] Hereinafter, the present invention will be described by way
of illustrative, but non-limiting examples with reference to the
accompanying drawings.
[0041] (Embodiment 1)
[0042] Hereinafter, a data control method according to Embodiment 1
of the present invention will be described with reference to FIGS.
1A to 1D, 2, 3, 4, and 5. FIGS. 1A to 1D are views for describing
the summary of the data control method in Embodiment 1. The term
"data control" as used in Embodiment 1 of the present invention
refers to copy control. As shown in FIG. 1A, a signal CI is a
signal dispersed over the entire image, and indicates copy
prohibition information 31 (FIG. 1B). A signal CE is a signal
inserted in a predetermined position of the image, and indicates
information 32 which permits the making of one copy (hereinafter,
referred to as a "one-time-copy-permitting information"). In the
case where copying is permitted N times, the number of permission
information 32 inserted in the image is N.
[0043] The signal CI is dispersed over the entire image, and thus
the signal CI is not visible. On the other hand, the signal CE is
inserted at a predetermined corner at the image, and the signal CE
may be visible or invisible.
[0044] FIG. 1B shows an image 33 whose copying is prohibited
(hereinafter, referred to as a "copy-prohibited image"). FIG. 1C
shows an image 34 whose copying is permitted once (hereinafter,
referred to as a "one-time-copy-permitted image"). A piece of the
permission information 32 is inserted in the lower right corner of
the image. FIG. 1D shows an image 35 whose copying is permitted
(hereinafter, referred to as a "copy-permitted image"), and no
prohibition information 31 is inserted over the entire image.
[0045] The copy control according to Embodiment 1 of the present
invention is intended to perform output control of an image signal
in accordance with three kinds of states, i.e., a copy-free state,
a N-times-copy-permitted state in which copying is permitted N
times (in the description hereinafter, N=1), and a copy-prohibited
state. In the copy-free state (i.e., copying is permitted), copying
is unconditionally permitted. In the one-time-copy-permitted state,
coping is permitted only once. In the copy-prohibited state, no
coping is permitted although displaying the image is allowed.
[0046] For the copy-prohibited image 33, the prohibition
information 31 is embedded as shown in FIG. 1B. When the
copy-prohibited image 33 is input to a device for recording data,
the permission information 32 is not detected, whereas the
prohibition information 31 is detected. In such a case, copying of
the image 33 is prohibited.
[0047] For the one-time-copy-permitted image 34, both of the
prohibition information 31 and the permission information 32 are
embedded as shown in FIG. 1C. If the permission information 32 is
detected prior to the copying of the image 34, copying of the image
is permitted. The device for recording data deletes the permission
information 32 of the image 34 which had been transmitted from a
transmitting medium to the device for recording data, and starts
copying the image 34. Regarding the deletion of the permission
information 32, the entire permission information 32 may be
deleted, or part of the permission information 32 may be deleted.
The purpose of such deletion is to make the permission information
impossible to be detected as the permission information 32, i.e.,
to invalidate the permission information. For example, in the case
where the permission information 32 has an 8-bit format, one bit of
such information may be deleted or all of the 8-bit of the
information may be deleted. Alternatively, in the case where the
permission information 32 is structured by the combination of two
pieces of information, one of the two pieces of the information may
be deleted.
[0048] Since only the permission information 32 is removed from the
image after copying, the prohibition information 31 is left behind,
thereby changing the image to the copy-prohibited image 33.
[0049] However, in the case of the N-time-copy-permitted-image in
which N pieces of the permission information (N is 2 or greater)
are embedded, one of the N pieces of the permission information is
deleted. As a result, the image becomes an
(N-1)-time-copy-permitted image.
[0050] For the copy-free image 35, at least the prohibition
information 31 is not embedded. When the copy-free image 35 is
copied, since the prohibition information 31 is not detected,
copying is permitted unconditionally.
[0051] According to the copy control method as described above, it
is possible to realize control such that copying is permitted N
times only, in addition to controlling copy prohibition and
permission. Moreover, it is not necessary to disclose the method
for embedding the prohibition information or the method for
deleting the prohibition information upon copying. Thus, this makes
it difficult for an unauthorized party to delete the prohibition
information. Furthermore, since the permission information is not
embedded upon copying, there is no need for disclosing the method
for embedding permission information. Therefore, it is impossible
for the unauthorized party to embed permission information.
Although the prohibition information is embedded across the entire
image according to the description made with reference to FIGS. 1A
to 1D, the prohibition information may be embedded in a certain
position in the image. Moreover, the permission information is
embedded in a predetermined position of the image as described
above in relation to FIGS. 1A to 1D. However, in the case where the
permitted number of copies is limited to 1, i.e., N=1, the
permission information may be embedded across the entire image.
[0052] Next, a method for embedding data control information and a
method for detecting data control information, which are
fundamental techniques for realizing the data control method
according to Embodiment 1 of the present invention, will be
described with reference to FIGS. 2 to 5.
[0053] FIG. 2 is a flow chart for illustrating the method for
embedding data control information according to Embodiment 1 of the
present invention. FIG. 4 is a flow chart for illustrating the
method for detecting data control information according to
Embodiment 1 of the present invention.
[0054] According to the method for embedding data control
information shown in FIG. 2, a variable Status which indicates one
of three states, i.e., (1) a copy-prohibited state; (2) a
one-time-copy-permitted state; and (3) a copy-free state, is set
first. In step S1, it is determined whether the variable status
indicates copy-free state or not. In the case where the variable
status indicates the copy-free state, the process is terminated. In
the case where the variable status does not indicate the copy-free
state, the process goes on to a step S2. In the step S2, the
prohibition information 31 is embedded in an image.
[0055] Such an embedding process may be any method for embedding
information of one bit or more in an image (e.g., the conventional
method for embedding copy control information). In particular, it
is more preferable that the method for embedding copy control
information is more complicated than the method for detecting the
copy control information. Under such a restriction, the effects of
the present invention are not ruined by the embedding method. Such
a method for embedding information in an image is refereed to as
Water Mark, and a large number of methods, including the method
described in the "DESCRIPTION OF THE RELATED ART", are known. For
example, a method introduced in "Water Mark protects multi-media
generation" (Nikkei Electronics, published in Feb. 24, 1997) is
known. At the next step S3, it is determined whether or not the
variable Status indicates the one-time-copy-permitted state. In the
case where the variable Status does not indicate the
one-time-copy-permitted state, the process is terminated. In the
case of the one-time-copy-permitted state, the process goes on to a
step S4.
[0056] At step S4, the permission information 32 is embedded in the
image. Step S4 is a process, for example, as shown in the flow
chart of FIG. 3. Hereinafter, the process for embedding the
permission information at the step S4 will be described in detail
with reference to FIG. 3.
[0057] At step S21, from pixels of an image or pixels of images in
which information is to be embedded, a code M which uniquely
corresponds to the image is extracted. The extraction of the code M
can be realized, for example, by a method in which k predetermined
pixels (k is an integer) are selected from the image, and the MBS
(i.e., most significant bit) of the data in these pixels is set to
be the code M of k bits. However, the process for extracting the
code M is not limited thereto. For example, a method in which k
blocks each having 8.times.8 pixels are selected from the image,
and the brightness values of these blocks is set to be the code M
of k bits, a method in which a frequency component in the image is
calculated, and low frequency components thereof are used as the
code M, or the like may be employed. Any extraction method may be
employed as long as the method can uniquely extract digital data
from the image.
[0058] At a next step S22, a digital signature f(M) is produced
using the code M. Hereinafter, the digital signature will be
described in detail.
[0059] Herein, it is assumed that a user A is a sender of an image
and a user B is a receiver of the image. Then, the case where the
code M of the image is converted to the signature C (C=f(M)), and
the signature is transmitted from user A to user B is considered.
User A produces the signature C and then transmits the image with
the signature C. User B authenticates the signature C, i.e.,
verifies whether the signature is valid or not.
[0060] Any digital signature can be used in Embodiment 1 of the
present invention as long as the signature satisfies the following
conditions:
[0061] (1) user B can readily authenticate the signature C; and
[0062] (2) user A can easily produce the signature C, but it is
difficult for a person other than the user A to produce the
signature C.
[0063] Specific examples of such a digital signature method include
a method utilizing public key cryptography. User A prepares a
signature function D (i.e., a first public key) as a function for
performing the signature, and prepares an authentication function E
(i.e., a second public key) as a function for performing
authentication. Herein, the authentication function E is set to be
an inverse function of the signature function D. User A uses the
signature function D so as to produce the signature C from the code
M according to the equation C=D(M). User B uses the authentication
function E so as to verify whether or not E(C) is identical with M.
Specifically, since the authentication function E is the inverse
function of the signature function D, if C is the valid signature,
the relationship such that E(C) E(D(M))=M is satisfied. On the
other hand, if the signature C is not valid, E(C) is not identical
with M.
[0064] According to this public key cryptography, a mechanism such
that the secret digital function D is difficult to derive from the
disclosed authentication function E is realized by using a
mathematical technique. Such examples include mechanisms utilizing
RSA cryptograph, Elgamal cryptograph, and the like. According to
the RSA cryptography, the signature function D is defined by the
following expression (1).
D(M)=M.sup.dmod n (1)
[0065] The authentication function E is defined by the following
expression (2).
E(C)=C.sup.emod n (2)
[0066] The term "mod n" herein refers to a remainder operation by
n, i.e., a remainder, which is an integer, resulting from the
division by n.
[0067] The terms "n", "e", and "d" in the above expressions (1) and
(2) are selected such that E becomes the inverse function of D.
Specifically, they are selected so as to satisfy the following
expression (3). 1 E ( C ) = C e mod n = ( M d ) 3 mod n = M de mod
n = M ( 3 )
[0068] User A prepares large prime numbers p and q, and sets that
n=p.times.q. Next, Euler's function .phi.(n), which is
(p-1).times.(q-1)=.phi.(n), is defined. Thereafter, an integer e
which constitutes a prime number with the function .phi.(n) is
suitably set. Specifically, the greatest common divider of .phi.(n)
and e is 1. Next, d is determined so as to satisfy the following
expression (4).
e.times.d mod .phi.(n)=1 (4)
[0069] By using the thus-determined e and d, aforementioned
expression (3) is satisfied.
[0070] User A discloses n and e, and keeps d, p, and q secret.
Accordingly, the authentication function E is disclosed, and the
signature function D is kept secret. User A who knows p and q can
derive d from e using expression (4). For user B who does not know
p and q, however, it is difficult to derive d from n and e.
[0071] To facilitate an understanding of the above, a very simple
numerical example will be described hereinafter. For example, if
p=5 and q=11 are selected as prime numbers. Then, n=55 and
.phi.(n)=40 are obtained from the aforementioned equations
n=p.times.q and (p-1).times.(q-1)=.phi.(n). Next, if e=7 is
selected, 7.times.23mod40=1 is obtained from the aforementioned
expression (4). Thus, d is 23. User A discloses n=55 and e=7, and
keeps p=5, q=11, and d=23 secret.
[0072] The signature for M=42, for example, will be calculated as
in the following expression (5).
D(M)=42.sup.23 mod 55=3 (5)
[0073] Accordingly, C equals 3. Using the disclosed authentication
function, user B performs the calculation of the following
expression (6).
E(C)=3.sup.7 mod 55=42 (6)
[0074] Consequently, since E(C) equals the original number of M,
i.e., M=42, it is authenticated that the signature is valid.
[0075] For the purpose of simplification, small values are selected
as prime numbers p and q which constitute n in the above-described
numerical example. In reality, however, in order to enhance the
security of cryptograph, n has the size of about 512 bits. Even if
the values of p and q are assumed to have a bit width of 256, the
value of n is enormous, i.e., the value of n has about 77 to 78
digits in terms of decimal number system.
[0076] The aforementioned description concerns the digital
signature using public key cryptography. However, a digital
signature based on a knapsack problem, a digital signature using
zero knowledge proof, and the like are known, and described in
"Cryptography and information security" written by Tujii and
Kasahara (published by Shoukoudou in 1990).
[0077] With reference to the flow charts shown in FIGS. 2 and 3
again, description of the method for embedding data control
information according to Embodiment 1 will be continued
hereinafter. After the digital signature f(M) is produced using the
code M at step S22 in FIG. 3, the signature f(M) is embedded in the
image at step S23. As a method for embedding the signature f(M) in
the image, there is a method in which the signature is embedded in
the edge of the image using a visible pattern such that 0 is
represented by white color and 1 is represented by black color.
However, the present invention is not limited to such a method. Any
signature embedding method may be employed as long as the method
embeds a code having a plurality of bits. For example, a method in
which LSB (i.e., the least significant bit) of a pixel selected
from the image is replaced with the signature f(M), a method in
which the signature f(M) is embedded between blanking areas of the
image, a method using Water Mark which can be easily deleted, or
the like may be used.
[0078] Since such a process for embedding permission information
uses the digital signature based on the code M which can be
uniquely derived from the image as the permission information, it
is difficult for a third party to produce the identical signature
without having the private key d. Thus, it is impossible to newly
embed permission information.
[0079] According to the method for embedding copy control
information in Embodiment 1 of the present invention, in the case
of copy-free image, nothing is embedded in the image. In the case
of one-time-copy-permitted image, the prohibition information and a
piece of permission information are embedded in the image. In the
case of copy-prohibited image, only the prohibition information is
embedded in the image.
[0080] Next, with reference to FIG. 4, a method for detecting data
control information (i.e., detecting copy control information) from
an image according to Embodiment 1 of the present invention will be
described.
[0081] First, at step S5, the permission information 32 is detected
from an image. Step S5 is a process, for example, as shown in the
flow chart of FIG. 5. With reference to FIG. 5, the process for
detecting the permission information at step S5 of FIG. 4 will be
described in detail hereinafter.
[0082] At a step S24 in FIG. 5, the signature f(M), which is
embedded in the image, is detected. In next step S25, the code M is
extracted from the image. In order to extract the code M, the same
process as that used for extracting the code M at step S21 in FIG.
3 may be employed.
[0083] At a next step S26, authentication of the digital signature
is performed. At this time, the signature produced at step S22 in
FIG. 3 is authenticated. In the case of the authentication for the
RSA cryptograph, for example, the disclosed information n and the
public key e are used. If the signature f(M) is assumed to be C,
the function for authenticating the signature is represented by the
aforementioned expression (2). If the result equals M as shown in
the aforementioned expression (3), the signature is authenticated.
On the other hand, if the result is not identical with M, the
signature is not authenticated.
[0084] The fact that the signature is authenticated indicates that
the permission information is embedded. Therefore, the process goes
on to step S27 and 1 is substituted for a permission flag. The fact
that the signature is not authenticated at step S26 indicates no
permission information is embedded. Therefore, the process goes on
to step S28 and 0 is substituted for the permission flag. Although
the permission flag is produced in the manner as described above in
Embodiment 1 of the present invention, any signal may be used as
long as the signal can identify the state where the permission
information is embedded and the state where the permission
information is not embedded.
[0085] After the permission information is detected in step S5 in
FIG. 4 as described above, the process goes on to a step S6, and
the determination of the permission flag is performed. If the
permission flag is 1, the process goes on to a step S7. If the
permission flag is 0, the process goes on to a step S8. At step S7,
the permission information is deleted. The deletion of the
permission information is a process for removing the permission
information which had been embedded in step S4 in FIG. 2 from the
image. Herein, at least part of the permission information is
deleted as described above. After the process at step S7 is
completed, the process goes on to a step S11, and a copy
permission/prohibition flag is set to be 1.
[0086] At step S8, the prohibition information is detected. The
detection herein refers to the detection of the prohibition
information which had been embedded at step S2 in FIG. 2. In the
case where the prohibition information is detected, the prohibition
flag is set to be 1. In the case where no prohibition information
is detected, the prohibition flag is set to be 0. Thereafter, the
process goes on to step 59, and the determination of the
prohibition flag is performed. If the prohibition flag is 1, the
process goes on to step S10. If the prohibition flag is 0, the
process goes on to step S11. A method for generating the
prohibition flag is not limited to the above-described method. Any
signal may be used as the prohibition f lag as long as the signal
can identify the state where the prohibition information is
embedded and the state where the prohibition information is not
embedded.
[0087] At step S10, the copy permission/prohibition flag is set to
be 0, and at step S11, the copy permission/prohibition flag is set
to be 1. Herein, the copy permission/prohibition flag is a signal
such that 0 represents the prohibition of copying and 1 represents
the permission of copying. Any form of the copying
permission/prohibition flag can be employed as long as the signal
can identify the prohibition of copying and the permission of
copying.
[0088] According to the method for detecting data control
information according to Embodiment 1 of the present invention,
copying of the image in which the permission information is
embedded is not permitted after the permission information is
deleted. For the image in which neither the permission information
nor the prohibition information is embedded, copying of the image
is permitted. For the image in which no permission information is
embedded and the prohibition information is embedded, copying of
the image is prohibited.
[0089] As described above, the change from the
one-time-copy-permitted state to the copy-prohibited state is
realized by a means of the embedding and deleting of the permission
information. Moreover, the embedding of the permission information
is based on the digital signature. Accordingly, the deletion or
detection of the permission information can be easily performed.
However, for a person who does not know the private key d, it is
difficult to embed permission information. Therefore, it is
difficult to change (i.e., rewrite) a copy-prohibited state to a
copy-permitted state in an unauthorized manner. Furthermore, the
prohibition information is embedded by using a method different
from the embedding method of the permission information. As a
result, it is only necessary to disclose or provide the detecting
method to user B. Thus, user A can keep the embedding or deleting
method secret.
[0090] According to Embodiment 1 of the present invention, in
addition to controlling for the prohibition and permission to copy,
it is possible to realize such control that copying is permitted
only once. Therefore, it is possible to realize a data control
method, or a method for embedding data control information and a
method for detecting the data control information, which make
tampering more difficult to conduct as compared to the conventional
method.
[0091] In Embodiment 1 of the present invention, the method which
realizes control such that copying is permitted only once is
described. However, it is also possible to realize control such
that copying is permitted N times by embedding N pieces of the
permission information (N is an integer greater than or equal to 2)
upon embedding copy control information, and deleting only one
piece of permission information regardless of the number of pieces
of permission information found upon detection.
[0092] In the above description, a data control method which
prohibits copying, a data control method which permits copying
once, and a data control method which permits copying N times are
described. However, the present invention is not limited thereto.
Similarly, it is also possible to realize, for example, control
such that the reproduction of an image is prohibited, the
reproduction of an image is permitted once, or the reproduction of
an image is permitted N times; control for data processing such as
editing or manipulation of an image; or control for the display of
an image.
[0093] Moreover, although the image signal is the subject for the
processing according to Embodiment 1 of the present invention, an
audio signal or a document may be subjected to such processing as
well. In such a case, the same effects as those described above can
be obtained.
[0094] Furthermore, although the digital signature based on the
code M which can be uniquely derived from an image is used as the
permission signal in Embodiment 1, the present invention is not
limited thereto. Any embedding method may be used. Specifically,
without disclosing the method for embedding the permission
information to user B, only the deletion method and the detection
method are disclosed to user B. If a method in which the embedding
method cannot be guessed from the deletion method or the detection
method, a method in which the calculation amount of the embedding
process is greater than that of the deletion or detection process,
a method using a large complicated circuit, or the like is
employed, it is possible to further increase tamper resistance. By
producing the permission information based on the code M which can
be uniquely derived from the image, the image can have one-to-one
correspondence with the permission information. This makes
unauthorized production of the permission information
difficult.
[0095] Other examples of the method for embedding the permission
information include a method in which permission information
consists of a first piece of permission information and a second
piece of permission information; and the first piece of permission
information is embedded in an image using a first embedding method,
and the second piece of permission information is simultaneously
embedded in the image using a second embedding method. Herein, an
embedding method which makes the deletion of the embedded
information difficult to perform, i.e., the same method as used for
embedding the prohibition information, is used as the first
embedding method. On the other hand, a method in which the
permission information is visibly embedded in the edge of the image
and thus the deletion thereof can be easily performed is used as
the second embedding method. Regarding the copying of the image,
only when both of the first piece of permission information and the
second piece of permission information are detected is copying
permitted, and only the second piece of permission information is
deleted. By the combination of the first piece of permission
information and the second piece of permission information as
described above, it is possible to realize an embedding method
whereby the detection and deletion of the permission information
are performed easily, but the unauthorized embedding of permission
information is difficult to perform. The first embedding method
herein may be the method same as, or different from, the method for
embedding the prohibition information.
[0096] Examples of the method constituting the first piece of
permission information and the second piece of permission
information include a method in which either the result of the
conversion processing of the code M by a conversion factor or the
conversion factor is set to be the first piece of permission
information, and the remaining result or conversion factor is set
to be the second piece of permission information. Herein, any
conversion processing method may be used as long as it is a process
such that the result of the conversion processing varies depending
on the value of its conversion factors. Examples of such a
conversion method include arithmetic operations such as addition,
subtraction, multiplication, or division using the conversion
factors, a logical operation using the conversion factor, an
encryption using the conversion factor as a key, a delay process
wherein the conversion factor is set as the amount of delay, and
the like. It is particularly preferable to employ conversion
processing such that it is difficult to derive a conversion factor
from the code M and the conversion result. This conversion method
has an effect of increasing tamper resistance. Such an effect can
be realized by keeping the method for the conversion processing
secret.
[0097] (Embodiment 2)
[0098] In Embodiment 2 of the present invention, a data control
system for realizing the data control method described in
Embodiment 1; and a device for embedding data control information
and a device for detecting data control information in said system
are described.
[0099] FIG. 6 is a view for illustrating the structure of the data
control system according to Embodiment 2 of the present invention.
The data control system includes: a device 41 for embedding data
control information (hereinafter, referred to simply as an
"embedding device"); a device 42 for detecting data control
information (hereinafter, referred to simply as a "detecting
device"); a transmitting section 43; a recording section 44; and a
recording medium 45. An image signal is input to the embedding
device 41, and copy control information is embedded in the image
signal. Thereafter, the image signal in which the copy control
information is embedded is output to the transmitting section
43.
[0100] Examples for the transmission method by the transmitting
section 43 include digital transmission or analog transmission by
means of radio utilizing a satellite or a ground wave, and digital
transmission or analog transmission by means of wire utilizing a
telephone line, a coaxial cable, a twisted pair cable, an optical
cable, or the like. In addition, a digital or analog recording
medium such as a magnetic disk, an optical disk, a CD, a DVD, a
DVC, a VCR, or the like is also considered to be the transmitting
section 43 since the image signal is reproduced from the recording
medium as a bit stream.
[0101] The image signal which is transmitted or reproduced via the
transmitting section 43 is input to the detecting device 42. In the
detecting device 42, the copy control information is detected, and
a recording permission/prohibition flag indicating whether or not
the copying is permitted and image information are output from the
detecting device 42. This information is input to the recording
section 44.
[0102] In the case where the recording permission/prohibition flag
indicates the permission to copy, the recording section 44 allows
the recording medium 45 to record the image information. In the
case where the recording permission/prohibition flag indicates
copying is prohibited, no recording is performed by the recording
section 44. The recording medium 45 may be any medium as long as it
performs the recording of data. Examples of the recording medium 45
include a magnetic disk, an optical disk, a CD, a DVD, a DVC, a
VCR, and the like.
[0103] The embedding device 41 includes a section 411 for embedding
prohibition information and a section 412 for embedding permission
information.
[0104] In the embedding device 41, if one-time-copy-permitting
information or copy-prohibiting information is to be embedded,
section 411 for embedding prohibition information embeds the
prohibition information in the input image signal. The process for
embedding the prohibition information is the same as that described
in the step S2 in FIG. 2. Thereafter, in the case where copying is
permitted once, section 412 for embedding permission information
embeds the permission information in the image signal. The
operation of section 412 for embedding permission information will
be described later.
[0105] According to the above-described operation of the embedding
device 41, no information is embedded in the image in the case of a
copy free image; the prohibition information and the permission
information are embedded in an image in the case where copying of
the image is permitted once; and the prohibition information is
embedded in an image in the case where copying of the image is
prohibited.
[0106] The detecting device 42 includes a section 421 for detecting
prohibition information, a section 422 for detecting and deleting
permission information, and a determining section 423.
[0107] In the detecting device 42, section 422 for detecting and
deleting prohibition information performs detection and deletion of
the permission information from the image signal. In the case where
the permission information is detected, a permission flag
indicating 1 is output. In the case where the permission
information is not detected, the permission flag indicating 0 is
output. The operation of section 422 for detecting and deleting
permission information will be described later.
[0108] When the image signal is input to section 421 for detecting
prohibition information from section 422 for detecting and deleting
permission information, section 421 for detecting prohibition
information examines whether or not the prohibition information is
embedded. If the prohibition information is detected, a prohibition
flag indicating 1 is output. If the prohibition information is not
detected, the prohibition flag indicating 0 is output. The values
of the permission flag and the prohibition flag are input to the
determining section 423. In the case where the permission flag is
1, or the prohibition flag is 0, determining section 423 outputs
the recording permission/prohibition flag indicating permission to
copy. In the case where the permission flag is 0 and the
prohibition flag is 1, the recording permission/prohibition flag
indicating that copying is prohibited is output by determining
section 423.
[0109] By the above-described operation of the detecting device 42,
the image in which the permission information is embedded is
allowed to be copied after the permission information is deleted.
For the image in which neither the permission information nor the
prohibition information is embedded, copying of the image is
permitted. For the image in which no permission information is
embedded and the prohibition information alone is embedded, copying
of the image is prohibited.
[0110] Next, the structures and operations of section 412 for
embedding permission information and section 422 for detecting and
deleting permission information will be described with reference to
FIGS. 7 and 8.
[0111] As shown in FIG. 7, section 412 for embedding permission
information includes a section 51 for embedding a signature
(hereinafter, referred to as "signature embedding section"), a
section 52 for extracting a code (hereinafter, referred to as "code
extracting section"), and a signature section 53.
[0112] In section 412 for embedding permission information, the
code extracting section 52 generates a code M which can be uniquely
derived from the image signal. Then, the code M is output to
signature section 53. Thereafter, signature section 53 converts the
code M to the digital signature f(M). The digital signature f(M) is
then output to signature embedding section 51. Subsequently,
signature embedding section 51 embeds the digital signature f(M) in
the image signal. In the case where the permission information is
not to be embedded, the process for embedding the digital signature
f(M) is not performed. Herein, the method for generating the code M
in code extracting section 52, the method for generating the
digital signature f(M) in signature section 53, and the method for
embedding the signature in signature embedding section 51 are the
same as the processes at steps S21, S22, and S23 in FIG. 3,
respectively.
[0113] As shown in FIG. 8, section 422 for detecting and deleting
permission information includes section 54 for extracting and
deleting a signature (hereinafter, referred to as "signature
extracting and deleting section"), section 55 for extracting a code
(hereinafter, referred to as "code extracting section"), and
authentication section 56.
[0114] In section 422 for detecting and deleting permission
information, the signature extracting and deleting section 54
extracts the digital signature f(M) from the image signal and
deletes at least part of the digital signature f(M) from the image
signal. Next, code extracting section 55 generates the code M from
the image signal in the same manner as that of code extracting
section 52. The code M is then output to authentication section 56.
Thereafter, authentication section 56 authenticates the digital
signature f(M) based upon the code M, and outputs the recording
permission/prohibition flag indicating whether recording is
permitted. If the digital signature f(M) is not authenticated, the
recording permission/prohibition flag indicating a prohibition
against recording is output. Herein, the method for extracting the
signature in the signature extracting and deleting section 54, the
method for generating the code M in the code extracting section 55,
and the authentication method in the authentication section 56 are
the same as those described with reference to FIG. 5,
respectively.
[0115] As described above, according to Embodiment 2 of the present
invention, in addition to controlling the prohibition and
permission to copy, it is possible to realize control such that
copying is permitted only once. Therefore, it is possible to
realize a data control system, and a device for embedding data
control information and a device for detecting the data control
information in said system, which make tampering more difficult to
conduct as compared to the conventional method.
[0116] In Embodiment 2 of the present invention, the method for
realizing control such that copying is permitted only once is
described. However, it is also possible to realize control such
that copying is permitted N times by embedding N pieces of
permission information (N is a natural number greater than or equal
to 1) upon embedding copy control information, and deleting only
one piece of permission information regardless of the number of
pieces of permission information found upon detection.
[0117] Moreover, a method for embedding copy prohibition
information and a method for detecting copy prohibition information
are described above. Similarly, it is also possible to realize a
method for embedding reproduction prohibition information and a
method for detecting the reproduction prohibition information.
Thus, control for reproduction can be performed. Furthermore, it is
possible to simultaneously realize control of copying and control
of reproduction.
[0118] Although the embedding device 41 has the structure as shown
in FIG. 6 in Embodiment 2 of the present invention, the structure
thereof is not limited thereto. The positions of section 411 for
embedding prohibition information and section 412 for embedding
permission information may be switched. The embedding device may
have any structure such that the device embeds at least the
prohibition information for an image whose copying is prohibited,
and embeds both of the prohibition information and the permission
information for an image whose copying is permitted once.
[0119] Although the detecting device 42 has the structure as shown
in FIG. 6, the structure thereof is not limited thereto. For
example, the image signal input to section 422 for detecting and
deleting permission information may be directly input to section
421 for detecting prohibition information. Also, the detecting
device 42 may have the structure such that section 422 for
detecting and deleting permission information is separated into a
device for detecting permission information and a device for
deleting the permission information, or the like. The detecting
device 42 may have any structure such that copying is permitted
upon the detection of the permission information and the permission
information is deleted, and copying is prohibited if the
prohibition information is detected.
[0120] Although the digital signature based on the code M which can
be uniquely derived from an image is used as the permission signal
in the embodiments described above, the permission signal is not
limited thereto. Any embedding method can be used. Specifically,
without disclosing the embedding method to user B, only the
deletion method and the detection method are disclosed. If a method
in which the embedding method cannot be guessed from the deletion
method or the detection method, a method in which the calculation
amount in the embedding process is greater than that of the
deletion or detection process, or a method using a large
complicated circuit, or the like is employed, it is possible to
further increase the tamper resistance. By producing the permission
information based on the code M which can be uniquely obtained from
the image, an image can have one-to-one correspondence with the
permission information. This makes the unauthorized production of
the permission information difficult.
[0121] Other examples of the method for embedding the permission
information include a method in which permission information
consists of a first piece of permission information and a second
piece of permission information; and the first piece of permission
information is embedded in an image using a first embedding method,
and the second piece of permission information is simultaneously
embedded in the image using a second embedding method. Herein, an
embedding method which makes the deletion of the embedded
information difficult to perform, i.e., the same method as used for
embedding the prohibition information, is used as the first
embedding method. On the other hand, a method in which the
permission information is visibly embedded in the edge of the image
and thus the deletion thereof can be easily performed is used as
the second embedding method. Regarding the copying of the image,
only when both of the first piece of permission information and the
second piece of permission information are detected is copying
permitted, and only the second piece of permission information is
deleted. By the combination of the first piece of permission
information and the second piece of permission information as
described above, it is possible to realize an embedding method
whereby the detection and deletion of the permission information
are performed easily, but the unauthorized embedding of permission
information is difficult to perform. The first embedding method
herein may be the method same as, or different from, the method for
embedding the prohibition information.
[0122] Examples of the method constituting the first piece of
permission information and the second piece of permission
information include a method in which either the result of the
conversion processing of the code M by a conversion factor or the
conversion factor is set to be the first piece of permission
information, and the remaining result or conversion factor is set
to be the second piece of permission information. Herein, any
conversion processing method may be used as long as it is a process
such that the result of the conversion processing varies depending
on the value of its conversion factors. Examples of such a
conversion method include arithmetic operations such as addition,
subtraction, multiplication, or division using the conversion
factors, a logical operation using the conversion factor, an
encryption using the conversion factors as a key, a delay process
wherein the conversion factor is set as the amount of delay, and
the like. It is particularly preferable to employ conversion
processing such that it is difficult to derive a conversion factor
from the code M and the conversion result. This conversion method
has an effect of increasing tamper resistance. Such an effect can
be realized by keeping the method for the conversion processing
secret.
[0123] In the above description of Embodiments 1 and 2, when status
is copy-free, method for embedding data control information or
device for embedding data control information does not embed data
control information. However, the present invention is not limited
thereto. When status is copy-free, it can embed information that
denotes copy-free in the data.
[0124] In the above description of Embodiments 1 and 2, method for
detecting data control information or device for detecting data
control information permits copy when data control information is
not detected. However, the present invention is not limited
thereto. When it does not detect data control information, it can
prevent data from copying. Alternatively, when it detects
information that denotes copy-free, it can permit the copying of
the data.
[0125] As described above, according to the present invention, in
addition to controlling copy-free permission and the prohibition of
copying, it is possible to realize control such that copying is
permitted only N times when the permission information is detected
in the data. Also, it is possible to realize a data control method
which makes tampering difficult to conduct.
[0126] According to one embodiment of the present invention, since
the producer of the data embeds the permission information in the
data using a digital signature, it is impossible for a person who
accesses the data to tamper with the permission information.
[0127] According to one embodiment of the present invention, in
addition to controlling copy-free permission and the prohibition
against copying, it is possible to embed information which permits
copying N times.
[0128] According to one embodiment of the present invention, since
the permission information is generated based on the code which can
be uniquely derived from the data, the permission information has a
one-to-one correspondence with the data. Thus, it is possible to
make tampering with the permission information difficult.
[0129] According to one embodiment of the present invention, it is
possible to limit the number of copies to N when data in which the
permission information is inserted is input, and it is possible to
prohibit copying when data in which the prohibition information
alone is inserted.
[0130] According to one embodiment of the present invention, only
when the permission information based on a code which can be
uniquely derived from the data is detected is copying
permitted.
[0131] According to one embodiment of the present invention, only
when the digital signature is authenticated is copying
permitted.
[0132] According to one embodiment of the present invention, when
the permission information is detected from data, data can be
recorded on a recording medium.
[0133] According to one embodiment of the present invention, when
the prohibition information alone is detected in data, the
processing of the data is prohibited; and when the permission
information is detected, it is possible to permit the processing of
the data N times.
[0134] According to one embodiment of the present invention, in
addition to controlling the prohibition of data processing, it is
possible to embed information which permits data processing N
times.
[0135] According to one embodiment of the present invention, when
data in which the permission information is inserted is input, the
number of times the data can be processed can be limited to N; and
when data in which the prohibition information alone is inserted is
input, data processing can be prohibited.
[0136] Various other modifications will be apparent to and can be
readily made by those skilled in the art without departing from the
scope and spirit of this invention. Accordingly, it is not intended
that the scope of the claims appended hereto be limited to the
description as set forth herein, but rather that the claims be
broadly construed.
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