U.S. patent application number 11/620923 was filed with the patent office on 2007-05-31 for recording medium, recording method and apparatus, reproducing method and apparatus, data transmitting method, and data decrypting method.
This patent application is currently assigned to Sony Corporation. Invention is credited to Shunsuke Furukawa, Tatsuya Inokuchi, Takashi Kihara, Yoichiro Sako.
Application Number | 20070124646 11/620923 |
Document ID | / |
Family ID | 27654488 |
Filed Date | 2007-05-31 |
United States Patent
Application |
20070124646 |
Kind Code |
A1 |
Inokuchi; Tatsuya ; et
al. |
May 31, 2007 |
RECORDING MEDIUM, RECORDING METHOD AND APPARATUS, REPRODUCING
METHOD AND APPARATUS, DATA TRANSMITTING METHOD, AND DATA DECRYPTING
METHOD
Abstract
A recording medium having an area in which data that has been
encoded with a first error correction code is recorded, wherein
data that can be decoded with a second error correction code that
is different from the first error correction code is recorded to
the area along with the data that has been encoded with the first
error correction code, and wherein the data that can be decoded
with the second error correction code composes at least part of
encryption key data.
Inventors: |
Inokuchi; Tatsuya; (Tokyo,
JP) ; Sako; Yoichiro; (Tokyo, JP) ; Furukawa;
Shunsuke; (Tokyo, JP) ; Kihara; Takashi;
(Chiba, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Sony Corporation
Tokyo
JP
|
Family ID: |
27654488 |
Appl. No.: |
11/620923 |
Filed: |
January 8, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10472492 |
Sep 30, 2003 |
|
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PCT/JP03/00526 |
Jan 22, 2003 |
|
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11620923 |
Jan 8, 2007 |
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Current U.S.
Class: |
714/758 ;
G9B/20.002; G9B/20.027; G9B/20.046; G9B/20.053; G9B/20.054 |
Current CPC
Class: |
G11B 20/00282 20130101;
H03M 13/2903 20130101; G11B 20/00086 20130101; G11B 2020/1461
20130101; H03M 13/2924 20130101; G11B 20/00528 20130101; G11B
20/00927 20130101; G11B 20/1217 20130101; H03M 13/2789 20130101;
G11B 20/0092 20130101; G11B 20/1866 20130101; G11B 20/18 20130101;
G11B 20/00202 20130101; G11B 20/1833 20130101; G11B 20/00297
20130101; G11B 2020/184 20130101; G11B 2220/2545 20130101; G11B
20/00913 20130101; G06F 21/10 20130101; G11B 20/00884 20130101;
G11B 20/0021 20130101; G11B 20/0063 20130101 |
Class at
Publication: |
714/758 |
International
Class: |
H03M 13/00 20060101
H03M013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2002 |
JP |
2002-024496 |
Claims
1-43. (canceled)
44. A reproducing method for a recoding medium, comprising the
steps of: decoding data that is read from an area of the recording
medium, data that has been encrypted and that has been encoded with
a first error correction code being recorded to the area, in the
area, data that can be decoded with a second error correction code
that is different from the first error correction code being
recorded along with the data encoded with the first error
correction code; generating decryption key data using data that has
been decoded with at least the second correction code; and
decrypting the data that has been encoded with the first error
correction code using the generated key data.
45. The reproducing method for the recording medium as set forth in
claim 44, further comprising the step of: generating the key data
using an error pattern of the data that has been decoded with the
second error correction code.
46. The reproducing method for the recording medium as set forth in
claim 44, wherein a reading position of data that can be decoded
with the second error correction code and that is read from the
area is changed whenever the data is reproduced from the recording
medium.
47. The reproducing method for the recording medium as set forth in
claim 44, wherein a reading order of data that can be decoded with
the second error correction code and that is read from the area is
changed whenever the data is reproduced from the recording
medium.
48. The reproducing method for the recording medium as set forth in
claim 44, wherein the key data generating step is performed by
reading the data from the area to a semiconductor memory and
generating the key data using data that is read to the
semiconductor memory.
49. The reproducing method for the recording medium as set forth in
claim 44, wherein the data that can be decoded with the second
error correction code is data that can be also decoded with the
first error correction code.
50. The reproducing method for the recording medium as set forth in
claim 44, wherein the first error correction code and the second
error correction code are used to encode at least two encoding
sequences in respective directions, the first error correction code
and the second error correction being different only in the
encoding sequences, the data that can be decoded being data of
which predetermined data is repeated as one unit of one of the two
encoding sequences in the respective directions.
51. The reproducing method for the recording medium as set forth in
claim 44, wherein the first error correction code and the second
error correction code are a code with which a C1 sequence in a
vertical direction is encoded and a code with which a C2 sequence
in a diagonal direction is encoded, respectively, the first error
correction code and the second error correction code being
different in their interleave lengths, the data that can be decoded
being predetermined data repeated as one unit of the C1
sequence.
52. A reproducing apparatus for a recoding medium, comprising: a
head portion for reading data from the recording medium, data that
has been encrypted and that has been encoded with a first error
correction code being recorded to the area, in the area, data that
can be decoded with a second error correction code that is
different from the first error correction code being recorded along
with the data encoded with the first error correction code; a
decoding process portion for performing a decoding process for an
output signal of the head portion; a generating portion for
decoding output data of the decoding process portion with the
second error correction code and generating decryption key data
using data that has been decoded with at least the second
correction code; and a decrypting portion for decrypting output
data of the decoding process portion using the generated key
data.
53. The reproducing apparatus for the recording medium as set forth
in claim 52, wherein the generating portion is configured to also
generate the key data using an error pattern of the data that has
been decoded with the second error correction code.
54. The reproducing apparatus for the recording medium as set forth
in claim 52, wherein a reading position of data that can be decoded
with the second error correction code and that is read from the
area is changed whenever the data is reproduced from the recording
medium.
55. The reproducing apparatus for the recording medium as set forth
in claim 52, wherein a reading order of data that can be decoded
with the second error correction code and that is read from the
area is changed whenever the data is reproduced from the recording
medium.
56. The reproducing apparatus for the recording medium as set forth
in claim 52, wherein the data that is read from the area is read to
a semiconductor memory and the key data is generated using data
that is read to the semiconductor memory.
57. The reproducing apparatus for the recording medium as set forth
in claim 52, wherein the data that can be decoded with the second
error correction code is data that can be also decoded with the
first error correction code.
58. The reproducing apparatus for the recording medium as set forth
in claim 52, wherein the first error correction code and the second
error correction code are used to encode at least two encoding
sequences in respective directions, the first error correction code
and the second error correction being different only in the
encoding sequences, the data that can be decoded being data of
which predetermined data is repeated as one unit of one of the two
encoding sequences in the respective directions.
59. The reproducing apparatus for the recording medium as set forth
in claim 52, wherein the first error correction code and the second
error correction code are a code with which a C1 sequence in a
vertical direction is encoded and a code with which a C2 sequence
in a diagonal direction is encoded, respectively, the first error
correction code and the second error correction code being
different in their interleave lengths, the data that can be decoded
being predetermined data repeated as one unit of the C1
sequence.
60-67. (canceled)
68. A data decrypting method, comprising the steps of: decoding
data with a second error correction code, the data having been
received as data that has been encrypted and that has been encoded
with a first error correction code along with data that can be
decoded with a second error correction code that is different from
the first error correction code; generating decryption key data
using data that has been decoded with at least the second error
code; and decrypting the data that has been encoded with the first
error correction code using the generated key data.
69. The data decrypting method as set forth in claim 68, further
comprising the step of: generating the key data using an error
pattern of the data that has been decoded with the second error
correction code.
70. The data decrypting method as set forth in claim 68, wherein a
reading position of data that can be decoded with the second error
correction code is changed whenever the data is decoded.
71. The data decrypting method as set forth in claim 44, wherein a
reading order of data that can be decoded with the second error
correction code is changed whenever the data is decoded.
72. The data decrypting method as set forth in claim 68, wherein
the key data generating step is performed by reading the data to a
semiconductor memory and generating the key data using data that is
read to the semiconductor memory.
73. The data decrypting method as set forth in claim 68, wherein
the data that can be decoded with the second error correction code
is data that can be also decoded with the first error correction
code.
74. The data decrypting method as set forth in claim 68, wherein
the first error correction code and the second error correction
code are used to encode at least two encoding sequences in
respective directions, the first error correction code and the
second error correction being different only in the encoding
sequences, the data that can be decoded being data of which
predetermined data is repeated as one unit of one of the two
encoding sequences in the respective directions.
75. The data decrypting method as set forth in claim 68, wherein
the first error correction code and the second error correction
code are a code with which a C1 sequence in a vertical direction is
encoded and a code with which a C2 sequence in a diagonal direction
is encoded, respectively, the first error correction code and the
second error correction code being different in their interleave
lengths, the data that can be decoded being predetermined data
repeated as one unit of the C1 sequence.
Description
TECHNICAL FIELD
[0001] The present invention relates to a recording medium on which
content data is recorded, a recording method, a recording
apparatus, a reproducing method, a reproducing apparatus, a data
transmitting method, and a data decrypting method.
BACKGROUND ART
[0002] Since optical discs such as a CD (Compact Disc) and a CD-ROM
(Compact Disc Read Only Memory) are easy to handle and are produced
at relatively low cost, they have been widely used as recording
mediums for storing data. In recent years, a CD-R (Compact Disc
Recordable) disc, on which data can be recorded once, and a CD-RW
(Compact disc ReWritable) disc, on which data can be rewritten,
have come out. Thus, data can be more easily recorded on such
optical discs than before. As a result, optical discs such as a
CD-DA (Compact Disc Digital Audio) disc, a CD-ROM disc, a CD-R
disc, and a CD-RW disc have become the mainstream of data recording
mediums. In addition, in recent years, audio data is compressed
according to compression-encoding system such as the MP3 (MPEG1
Audio Layer-3) and the ATRAC (Adaptive TRansform Acoustic Coding) 3
and recorded on the CD-ROM disc, the CD-R disc, the CD-RW disc, and
so forth.
[0003] However, as the CD-R disc and the CD-RW disc have come out,
data recoded on the CD-DA disc can be more easily copied than
before. As a result, a problem about copyright protection has
arisen. Thus, when content data is recorded to the CD-R disc or the
CD-RW disc, it is necessary to take measures to protect content
data.
[0004] As one method for protecting content data recorded on the
CD-DA disc, the content data is encrypted and recorded on the CD-DA
disc. When content data is encrypted and recorded on a disc, unless
key data with which the content data is decrypted is obtained, the
content data cannot be decrypted. Thus, the content data can be
protected.
[0005] However, when encryption key data and a disc are separately
distributed, a particular system is required and becomes
troublesome. Thus, it is preferred to bury encryption key data on a
disc. However, it was difficult to record encryption key data on a
disc in such a manner that the encryption key data cannot be easily
known. That is because it is necessary to prevent buried encryption
key data from adversely affecting a conventional CD player, which
has been widely used.
[0006] Therefore, an object of the present invention is to provide
a recording medium, a recording method, a recording apparatus, a
reproducing method, a reproducing apparatus, a data transmitting
method, and a data decrypting method that allow copyright to be
securely protected using buried encryption key data with which
encrypted data is decrypted.
DISCLOSURE OF THE INVENTION
[0007] Claim 1 of the present invention is a recording medium
having an area in which data that has been encoded with a first
error correction code is recorded, wherein data that can be decoded
with a second error correction code that is different from the
first error correction code is recorded to the area along with the
data that has been encoded with the first error correction code,
and wherein the data that can be decoded with the second error
correction code composes at least part of encryption key data.
[0008] Claim 11 of the present invention is a recording method for
a recording medium, comprising the steps of recording data that has
been encoded with a first error correction code to a recording area
of the recording medium; and recording data that composes at least
a part of encryption key data and that can be decoded with a second
error correction code that is different from the first error
correction code to the area along with the data that has been
encoded with the first error correction code.
[0009] Claim 22 of the present invention is a recording method for
a recording medium, comprising the step of recording data that has
been encoded with a first error correction code to an area of the
recording medium along with a plurality of pieces of data that can
be decoded with the first error correction code and that can be
also decoded with a second error correction code that is different
from the first error correction code as a pattern that represents
at least a part of the encryption key data.
[0010] Claim 34 of the present invention is a recording apparatus
for a recording medium, comprising an encoding process portion for
performing an encoding process including an error correction code
encoding process for input data with a first error correction code;
a recording portion for receiving output data of the encoding
process portion and recording the received data to the recording
medium; and a generating portion for generating data that can be
decoded with the first error correction code, that composes at
least a part of encryption key data, and that can be decoded with a
second error correction code that is different from the first error
correction code and supplying the generated data to the encoding
process portion.
[0011] Claim 44 of the present invention is a reproducing method
for a recoding medium, comprising the steps of decoding data that
is read from an area of the recording medium, data that has been
encrypted and that has been encoded with a first error correction
code being recorded to the area, in the area, data that can be
decoded with a second error correction code that is different from
the first error correction code being recorded along with the data
encoded with the first error correction code; generating decryption
key data using data that has been decoded with at least the second
correction code; and decrypting the data that has been encoded with
the first error correction code using the generated key data.
[0012] Claim 52 of the present invention is a reproducing apparatus
for a recoding medium, comprising a head portion for reading data
from the recording medium, data that has been encrypted and that
has been encoded with a first error correction code being recorded
to the area, in the area, data that can be decoded with a second
error correction code that is different from the first error
correction code being recorded along with the data encoded with the
first error correction code; a decoding process portion for
performing a decoding process for an output signal of the head
portion; a generating portion for decoding output data of the
decoding process portion with the second error correction code and
generating decryption key data using data that has been decoded
with at least the second correction code; and a decrypting portion
for decrypting output data of the decoding process portion using
the generated key data.
[0013] Claim 60 of the present invention is a data transmitting
method, comprising the step of outputting data that has been
encoded with a first error correction code along with data that
composes a part of encryption key data that can be decoded with the
first error correction code and that can be also decoded with a
second error correction code that is different from the first error
correction code.
[0014] Claim 68 of the present invention is a data decrypting
method, comprising the steps of decoding data with a second error
correction code, the data having been received as data that has
been encrypted and that has been encoded with a first error
correction code along with data that can be decoded with a second
error correction code that is different from the first error
correction code; generating decryption key data using data that has
been decoded with at least the second error code; and decrypting
the data that has been encoded with the first error correction code
using the generated key data.
[0015] On an optical disc as a data recording medium, an area that
has been encoded according to the CIRC7 system that is a first
error correction code is formed. Content data is encrypted, encoded
according to the CIRC4 system that is a second error correction
code, and recorded. In the area in which data has been encoded
according to the CIRC7 system, data that can be corrected according
to both the CIRC4 system and the CIRC7 system is recorded at a
predetermined position in a predetermined pattern. As the data that
can be corrected according to both the CIRC4 system and the CIRC7
system, predetermined data is repeated in the unit of a C1
sequence. When data is decoded in those areas, data that can be
corrected is obtained. When data is decoded according to the CIRC4
system, information that represents whether or not there is a
correction impossible error is obtained. That data and information
are used as an encryption key.
[0016] According to the present invention, an encryption key can be
recorded without influence of a conventional CD drive and a
conventional CD-ROM. To improve the secrecy of the encryption key,
the position of the area on the disc, the position of data in the
area, and so forth are kept secret. Preferably, the structure of
data in the area is changed for each disc and for each stamper. In
addition, when the encryption key is read from the area, by various
measures, the secrecy of the encryption key is improved.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a plan view for describing an optical disc
according to the present invention.
[0018] FIG. 2 is a schematic diagram for describing the optical
disc according to the present invention.
[0019] FIG. 3 is a schematic diagram for describing a recording
format of the optical disc according to the present invention.
[0020] FIG. 4 is a schematic-diagram for describing the recording
format of the optical disc according to the present invention.
[0021] FIG. 5 is a block diagram showing an example of a CIRC
encoder.
[0022] FIG. 6 is a detailed block diagram showing the example of
the CIRC encoder.
[0023] FIG. 7 is a block diagram showing an example of a CIRC
decoder.
[0024] FIG. 8 is a detailed block diagram showing the example of
the CIRC decoder.
[0025] FIG. 9 is a schematic diagram for describing interleaving
according to the CIRC4 system.
[0026] FIG. 10 is a schematic diagram for describing interleaving
according to the CIRC7 system.
[0027] FIG. 11 is a schematic diagram for describing data that can
be corrected according to both the CIRC4 system and the CIRC7
system.
[0028] FIGS. 12A and B are schematic diagrams for describing an
area that has been encoded according to the CIRC7 system on the
optical disc according to the present invention.
[0029] FIGS. 13A and B are schematic diagrams for describing an
area that has been encoded according to the CIRC7 system on the
optical disc according to the present invention.
[0030] FIGS. 14A an B are schematic diagrams for explaining an area
that has been encoded according to the CIRC7 system on the optical
disc according to the present invention.
[0031] FIGS. 15A and B are schematic diagrams for describing an
area that has been encoded according to the CIRC7 system on the
optical system according to the present invention.
[0032] FIGS. 16A and B are schematic diagrams for describing an
area that has been encoded according to the CIRC7 system on the
optical disc according to the present invention.
[0033] FIG. 17 is a schematic diagram for describing an area that
has been encoded according to the CIRC7 system on the optical disc
according to the present invention.
[0034] FIG. 18 is a schematic diagram for describing another
example of an optical disc according to the present invention.
[0035] FIG. 19 is a block diagram showing an example of an optical
disc recording apparatus according to the present invention.
[0036] FIG. 20 is a block diagram showing an example of an optical
disc reproducing apparatus according to the present invention.
BEST MODES FOR CARRYING OUT THE INVENTION
[0037] Next, with reference to the accompanying drawings, an
embodiment of the present invention will be described. As a
recording medium according to the present invention, a
multi-session optical disc is used. The optical disc according to
the present invention has almost the same physical standard such as
size as a CD. Information on the optical disc can be optically read
by a conventional CD player and a CD-ROM drive.
[0038] On the optical disc according to the present invention,
encrypted content data has been recorded. The encrypted content
data is for example CD-ROM format or CD-DA format audio or video
content data that has been encrypted. As an example of the
encrypting system, the DES (Data Encryption Standard) can be used.
The DES is a block encoding system of which plain text is
block-segmented and encrypted block by block. In the DES, an input
of 64 bits is encrypted with key data of 64 bits (a key of 56 bits
and a parity of eight bits). As a result, 64 bits are output.
Alternatively, another encrypting system other than the DES can be
used. Although the DES is a common key system that uses the key
data for both encryption and decryption. Alternatively, the RSA
encryption, which is a public key encryption that use different key
data for encryption and decryption, may be used. When necessary,
content data has been compression-encoded according to the ATRAC3
(Adaptive TRansform Acoustic Coding 3), the MP3 (MPEG1 Audio
Layer-3), the AAC (MPEG Advanced Audio Coding), the TwinVQ, or the
like.
[0039] As shown in FIG. 1, the optical disc 1 according to the
present invention has a diameter of 120 mm. At the center of the
optical disc 1, a hole 2 is formed. The optical disc 1 may have a
diameter of 80 mm, which is same as so-called CD single disc.
[0040] As the optical disc 1, there are a reproduction-only disc, a
recordable disc, and a rewritable disc.
[0041] When the optical disc is a reproduction-only optical disc, a
reflection film made of aluminum is formed as a recording layer.
When the optical disc 1 is a reproduction-only optical disc, data
is recorded as physical pits. Normally, the disc is produced by an
injection molding method using a stamper.
[0042] When the optical disc is a rewritable optical disc, an
organic coloring matter such as phthalocyanine or cyanine is used
for a recording layer. When data is written to the recordable
optical disc, the temperature of the recording layer made of an
organic coloring matter of the disc is raised by a laser beam. As a
result, the recording layer made of the organic coloring matter is
thermally deformed.
[0043] When the optical disc is a rewritable optical disc, a phase
change material is used for a recording layer. As an example of the
phase change material, an alloy of Ag--In--Sb--Te
(silver--indium--antimony-tellurium) is used. Such a phase change
material has a crystal phase and an amorphous phase. When the
intensity of the laser beam is strong, the recording layer made of
the phase change material is heated over its melting point and then
rapidly cooled. As a result, the recording layer made of the phase
change material becomes the amorphous state. When the intensity of
the laser beam is relatively weak, the recording layer made of the
phase change material is heated to around the crystallization
temperature and then gradually cooled. As a result, the recording
material becomes the crystallization state. As a result, data is
recorded to the optical disc or erased therefrom.
[0044] As shown in FIG. 1 and FIG. 2, on the innermost periphery of
the optical disc 1, a first lead-in area LI1 is formed. On an outer
periphery of the area LI1, a first program area PA1 is formed.
Outside the first program area PA1, a first lead-out area LO1 is
formed. In the first program area PAl, in the same recording format
as the CD-DA standard, audio data is recorded. Since the recording
format of data in the first program area PA1 is the same as that of
the CD-DA standard and the data has not been encrypted, the data
can be reproduced by a conventional music reproduction CD
player.
[0045] Outside the first lead-out area LO1, a second lead-in area
LI2 is formed. On an outer periphery of the area LI2, a second
program area PA2 is formed. Outside the second program area PA2, a
second lead-out area LO2 is formed. In the second program area PA2,
as content data, audio data that has been compressed according to a
compression-encoding system such as the ATRAC3 is encrypted and
recorded.
[0046] In addition, the second program area PA2 contains two areas
AR1 and AR2 that are different in error correction code encoding
systems. In the area AR1, data is encoded with an error correction
code according to the same error correction code encoding system as
that of a conventional CD-DA disc and a conventional CD-ROM disc
(hereinafter, that system is referred to as CIRC (Cross Interleave
Reed-Solomon Code) 4 system) and recorded. In the area AR2, data is
encoded with an error correction code according to an error
correction code encoding system that will be used for a
double-density CD disc (hereinafter that system is referred to as
CIRC7 system) and recorded. As will be described above, in the area
AR2, a pattern of data that can be also corrected according to the
CIRC4 system is contained.
[0047] In the program area AR1, to have compatibility with the
CD-DA standard, data is encoded with an error correction code
according to the CIRC4 system.
[0048] Normally, an error correction code is added to detect a
burst error and a random error and perform a correcting process. As
will be described later, according to the embodiment, using
characteristics of error correction codes according to the CIRC4
system and the CIRC7 system, an encryption key is buried in the
area AR2.
[0049] In CDs, as an error correction code encoding system, a CIRC
of which an error correction code encoding process is dually
performed for a C1 sequence (in the vertical direction) and a C2
sequence (in the diagonal direction) is used. Data that has been
encoded with the error correction code is EFM (eight to fourteen
modulation) modulated in the unit of one frame and recorded.
[0050] FIG. 3 shows one frame of a CD data structure that has not
been EFM modulated. As shown in FIG. 3, when audio data is sampled
with 16 bits, one frame is composed of 24 symbols of data bits,
four symbols of a Q parity, four symbols of a P parity, and one
symbol of a sub code. 24 symbols of data bits are composed of six
samples on the left (L) and six samples on the right (R). One
symbol is made of eight bits of which 16 bits are divided by two.
Data of one frame recorded on the disc is converted from eight bits
into 14 bits by the EFM modulation. In addition, a direct current
component suppression bit and a frame sync are added to data of one
frame.
[0051] Thus, one frame recorded on the disc is composed of:
TABLE-US-00001 Frame sync 24 channel bits Data bits 14 24 = 336
channel bits Sub code 14 channel bits Parity 14 8 = 112 channel
bits Margin bits 3 34 = 102 channel bits
Thus, the total channel bits of one frame are 588 channel bits.
[0052] A collection of 98 frames is referred to as one sub code
frame. One sub code frame is equivalent to 1/75 second of a
reproduction time of a conventional CD. FIG. 4 shows a sub code
frame of which 98 frames are rearranged so that they are successive
in the vertical direction. One symbol of a sub code of each frame
contains bits of eight channels P to W. As shown in FIG. 4, one
sector is composed of data in the period (98 frames) for sub code.
The first two frames of 98 frames are sub code frame syncs SO and
Si. When data is recorded to an optical disc such as a CD-ROM, one
sector is composed of 98 frames (2,352 bytes), which is a sub code
completion unit.
[0053] FIG. 5 and FIG. 6 are block diagrams showing a flow of an
encoding process according to the CIRC system. For simplicity, the
encoding process/decoding process according to the CIRC system will
be described for audio data.
[0054] 24 symbols (W12n,A, W12n,B, . . . , W12n+11, A, W12n+11,B)
of which one word of an audio signal is divided into high order
eight bits and low order eight bits) (high order eight bits are
denoted by A and lower eight bits by B) are supplied to a
two-symbol delaying/scrambling circuit 11. The two-symbol
delaying/scrambling circuit 11 delays each of the even word data
L6n, R6n, L6n+2, R6n+2, . . . by two symbols. Even if all the
corresponding sequence has an error in a C2 encoder 12, the
two-symbol delaying/scrambling circuit 11 interpolates it. The
two-symbol delaying/scrambling circuit 11 scrambles the 24 symbols
so that the maximum burst error interpolation length can be
obtained.
[0055] Outputs of the two-symbol delaying/scrambling circuit 11 are
supplied to the C2 encoder 12. The C2 encoder 12 encodes (28, 24,
5) Reed-Solomon code on the Galois field GF (28) and generates
four-symbol Q parities Q12n, Q12+1, Q12n+2, and Q12n+3.
[0056] 28 symbols that are output from the C2 encoder 12 are
supplied to an interleaving circuit 13. The interleaving circuit 13
assigns delay amounts that vary in arithmetic progression such as
0, D, 2D, . . . , (where D represents a unit delay amount) to each
symbol so as to change one array of a symbol to a second array.
[0057] Outputs of the interleaving circuit 13 are supplied to a C1
encoder 14 that uses (32, 28, 5) Reed-Solomon code on the Galois
field (GF 28) as a C1 code. The C1 encoder 14 generates four-symbol
P parities P12n, P12n+1, P12n+2, and P12 n+3. The minimum distance
of each of the C1 code and C2 code is 5. Thus, the C1 encoder 14
can correct a two-symbol error and erasure-correct a four-symbol
error (in the case that the position of an error symbol is
known).
[0058] 32symbols that are output from the C1 encoder 14 are
supplied to a one-symbol delaying circuit 15. The one-symbol
delaying circuit 15 separates adjacent symbols so as to prevent an
error that spreads over a boundary of one symbol from resulting in
a two-symbol error. The Q parity is inverted by an inverter. Thus,
even if all data and parities become zero, an error can be
detected.
[0059] The unit delay amount D of the interleaving circuit 13
according to the CIRC4 system is different from that according to
the CIRC7 system. The interleaving circuit 13 disperses a burst
error.
[0060] In other words, according to the CIRC4 system, the
interleaving circuit 13 designates D=4 frames and separates
adjacent symbols by four frames each. The CIRC4 system of D=4
frames is used in the current CD-DA. According to the CIRC4 system,
the maximum delay amount becomes 27D (=108 frames). The total
interleave length becomes 109 frames.
[0061] According to the CIRC7 system, the interleaving circuit 13
designates D=7 frames and separates adjacent symbols by seven
frames each. The CIRC7 system of D=7 frames has been proposed for a
double density CD. According to the CIRC7 system, the maximum delay
amount becomes 27D (=189 frames). The total interleave length
becomes 190 frames.
[0062] FIG. 7 and FIG. 8 are block diagrams showing a flow of the
decoding process. The decoding process is performed in the reverse
order of the forgoing encoding process.
[0063] Reproduction data that is output from the EFM demodulating
circuit is supplied to a one-symbol delaying circuit 21. The delay
assigned by the one-symbol delaying circuit 15 on the encoding side
is cancelled by the circuit 21.
[0064] 32 symbols that are output from the one-symbol delaying
circuit 21 are supplied to a C1 decoder 22. Outputs of the C1
decoder 22 are supplied to a de-interleaving circuit 23. The
de-interleaving circuit 23 assigns delay amounts 27D, 26D, . . . ,
D, and 0 that vary in arithmetic progression to the 28 symbols so
that the delay amounts assigned by the interleaving circuit 13 are
cancelled.
[0065] According to the CIRC4 system, the unit delay amount of the
de-interleaving circuit 23 is D=4 frames. According to the CIRC7
system, the unit delay amount of the de-interleaving circuit 23 is
D=7 frames.
[0066] Outputs of the de-interleaving circuit 23 are supplied to a
C2 decoder 24. The C2 decoder 24 decodes the outputs of the
de-interleaving circuit 23 with the C2 code. 24 symbols that are
output from the C2 decoder 24 are supplied to a two-symbol
delaying/descrambling circuit 25. 24 symbols of decoded data are
obtained from the two-symbol delaying/descrambling circuit 25.
[0067] With error flags that are output from the C1 decoder 22 and
the C2 decoder 24, an interpolation flag generating circuit 26
generates an interpolation flag. With the interpolation flag, data
that represents an error is interpolated.
[0068] In such a manner, according to the CIRC, the error
correction code encoding process is performed with the C1 sequence
in the vertical direction. In addition, the error correction code
encoding process is performed with the C2 sequence in the diagonal
direction. Thus, the error correction code encoding process is
dually performed. The CIRC4 system and the CIRC7 system differ in
their interleave lengths.
[0069] According to the CIRC4 system, as shown in FIG. 9, the unit
delay amount D is (D=4). The total interleave length is 109
(=108+1) frames. Thus, according to the CIRC4 system, the total
interleave length is slightly larger than the data length of one
sector. According to the CIRC7 system, as shown in FIG. 10, the
unit delay amount D is (D=7). The total interleave length is 190
(=189+1) frames. Thus, according to the CIRC7 system, the total
interleave length is slightly shorter than the data length of two
sectors.
[0070] The total interleave length defines an error correction
performance against a burst error of which many pieces of data
successively become errors due to a fingerprint adhered on an
optical disc, a scratch on an optical disc, or the like. The longer
the total interleave length, the higher the burst error correction
performance is. In a double density CD, it is desired to improve a
correction performance against a burst error. Thus, for a double
density CD, it is considered to improve the correction performance
against the burst error with an error correction code according to
the CIRC7 system.
[0071] As described above, on the optical disc according to the
present invention, data that has been encoded with an error
correction code according to the CIRC7 system is recorded to the
area AR2. In addition, a pattern of data that can be corrected
according to both the CIRC7 system and the CIRC4 system is
contained in the area AR2. Next, data that can be corrected
according to both the CIRC7 system and the CIRC4 system will be
described.
[0072] As was described above, since the CIRC4 system and the CIRC7
system differ in their interleave lengths, data that has been
encoded with the error correction code according to the CIRC7
system cannot be decoded by a decoder according to the CIRC4
system. In contrast, data that has been encoded with the error
correction code according to the CIRC4 system cannot be decoded by
the decoder according to the CIRC7 system.
[0073] However, data having a particular arrangement can be decoded
by both the decoder according to the CIRC4 system and the decoder
according to the CIRC7 system. That means that the data can be
logically corrected (correction impossibility does not take place).
Thus, when an optical disc has a large scratch or the like, of
course, it results in correction impossibility.
[0074] FIG. 11 describes a data array that can be decoded by any
one of a decoder according to the CIRC4 system and a decoder
according to the CIRC7 system. In the data array shown in FIG. 11,
when data is two-dimensionally arrayed, predetermined data is
repeated as one unit in the vertical direction, namely in the unit
of a C1 sequence. In the example, data is repeated as one unit of
a1, a2, a3, and a4 in the vertical direction.
[0075] In such a data array, the same data is arranged in the
horizontal direction. In other words, as shown in FIG. 11, data of
the first row in the horizontal direction is all a1. Data of the
second row in the horizontal direction is all a2. Data of the third
row in the horizontal direction is all a3. Data of the fourth row
in the horizontal direction is a4. In such a manner, the same data
is arranged in the horizontal direction.
[0076] When data is arrayed in such a manner, like the C1 sequence,
the C2 sequence according to the CIRC4 system is the same as the C2
sequence according to the CIRC7 system. In other words, in the
example shown in FIG. 11, regardless of the total interleave length
(namely, the angle of the diagonal direction), the parity of the C2
sequence is always composed of a1, a2, a3, and a4.
[0077] Thus, when data is arrayed in such a manner, data that has
been encoded with the error correction code according to the CIRC7
system can be decoded by a decoder according to the CIRC4 system.
Reversely, data that has been encoded with the error correction
code according to the CIRC4 system can be decoded by a decoder
according to the CIRC7 system.
[0078] Thus, since the interleave length according to the CIRC4
system is different from the interleave length according to the
CIRC7 system, when data that has been encoded with the error
correction code according to the CIRC7 system is decoded by a
decoder according to the CIRC4 system or when data that has been
encoded with the error correction code according to the CIRC4
system is decoded by a decoder according to the CIRC7 system, a
correction impossibility error is detected. However, as was
described above, with an array of which predetermined data is
repeated in the vertical direction, the data can be decoded by any
one of a decoder according to the CIRC7 system and a decoder
according to the CIRC4 system.
[0079] According to the embodiment of the present invention, using
a characteristic of data that can be corrected by a decoder
according to the CIRC7 system and a decoder according to the CIRC4
system, encryption key data is recorded to a disc. Using the CIRC7
system, encryption key data cannot be reproduced by a conventional
CD player and a conventional CD-ROM drive. As a result, the secrecy
of the encryption key data can be improved. In addition, to improve
the secrecy, various measures are taken. As one measure, the
position of the area AR2 is kept secret. Next, a data recording
method and a data recording method for the area AR2 will be
described in practice.
[0080] FIG. 12A shows a structure of for example one track (one
music program of music data) recorded to the area AR2 of the second
program area PA2 on the optical disc 1 shown in FIG. 1 and FIG.
2.
[0081] As was described above, in the area AR2, a data pattern that
has been encoded with an error correction code according to the
CIRC7 system and that can be corrected according to both the CIRC7
system and the CIRC4 system is contained. In FIGS. 12A and B, data
A, dummy data, . . . , dummy data, data B, and data C represent
recorded portions that can be corrected according to both the CIRC7
system and the CIRC4 system is recorded. The other portions
(hatched areas) represents recorded portions that are detected as
error correction impossible portions when they are decoded
according to the CIRC4 system. Data that can be corrected according
to both the CIRC7 system and the CIRC4 system is data of which
predetermined data is repeated as one unit in the vertical
direction (C1 sequence).
[0082] When the area AR2 is decoded according to the CIRC4 system,
the data A can be corrected. Thus, no error is detected from the
data A (denoted by No in FIG. 12A). In contrast, hatched areas are
detected as error correction impossible portions (denoted by Yes in
FIG. 12A). In the example, if no error is decoded, there are two
cases. In the first case, the original data does not contain an
error. In the second case, an error contained in data is corrected.
In reality, there is a possibility of which an error cannot be
corrected according to the CIRC4 system due to a scratch, a
fingerprint, or the like on an optical disc.
[0083] Although an error correcting process is performed for each
of the C1 sequence and the C2 sequence, an error correction
impossible state is detected with an error corrected result that is
read (sampled) at a predetermined position of the C2 sequence. In
each portion, data of for example several ten bytes has been
recorded. Thus, error corrected results of the C2 sequence can be
securely read. In that case, a plurality of error corrected results
may be read at individual positions so as to securely detect error
corrected results of the C2 sequence. Assuming that when errors are
corrected according to the CIRC4 system, an error correction
impossible portion is assigned one bit "0" and a no-error portion
(of which an error can be corrected) is assigned one bit "1", data
D (0101 . . . 01101) is obtained.
[0084] According to the embodiment of the present invention, the
data A, B, and C, which can be corrected according to the CIRC4
system, are used as encryption key data or a part thereof. In
addition, according to the embodiment, the data D, which represents
error correction impossible portions and error correction possible
and no-error portions, is used as encryption key data or a part
thereof. In other words, when encryption key data is denoted by
CIRC7 -key, the encryption key data is generated by the following
formula. CIRC7-key=f.sub.1(A, B, C, and D) where f.sub.1 is a
particular key generation function. To further improve the secrecy
of the encryption key, dummy data is recorded.
[0085] There are several methods for improving the secrecy of
encryption key data. The method shown in FIG. 12A is referred to as
first recording method, whereas FIG. 12B shows a second recording
method. When the second recoding method is compared with the first
recording method, the positions of data (A, B, and C) of which no
correction impossibility take place according to both the CIRC4
system and the CIRC7 system have been changed. In addition, the
reading position of error corrected results have been changed. In
addition, the key generation function f.sub.1 has been changed to
f.sub.2. Whenever data is recorded to a recordable optical disc,
the first recording method and the second recording method are
alternately used. As a result, the secrecy of the encryption key
data can be improved. When a read-only optical disc is used, that
process is performed in a mastering process. For example, a
plurality of stampers according to the first recording method and
the second recording method are produced.
[0086] When application software that runs on a personal computer
(PC) using a PC drive reads key data, position information thereof
may be obtained from commands issued to the drive. To prevent such
a problem, the following process will be performed.
[0087] FIGS. 13A and B show a method for improving the secrecy of
encryption key data using the reading method for the encryption key
data. Data for example A that can be corrected according to both
the CIRC7 system and the CIRC4 system is recorded at a plurality of
positions in the area AR2. When the data A is read from the area
AR2, the reading position is changed. In FIG. 13A, the first data A
is read. In FIG. 13B, the second data A is read. For example, the
reading position is changed whenever a reproduction is performed.
Besides the data A, that method can be applied to the data B, data
C, and dummy data.
[0088] FIGS. 14A and B shows a method for improving the secrecy of
encryption key data using the reading method for the encryption key
data. In this example, the reading method for the data D is changed
depending on error correction impossible or error correction
possible. In other words, as shown in FIG. 14A and FIG. 14B, the
reading positions are changed. For example, whenever a reproduction
is performed, the reading positions are changed. In that case, even
if the reading positions are changed, the obtained data D is the
same.
[0089] FIG. 15A shows a method for reading predetermined data and
other data with one read command as denoted by an arrow mark in the
case that the predetermined data that can be corrected according to
both the CIRC4 system and the CIRC7 system is recorded at a
predetermined position. FIG. 15B shows a method for issuing not
only a true read command (command 2) for reading predetermined data
but false read commands (command 1 and command 2) so as to cause
the predetermined data not to be easily seen.
[0090] In FIG. 16A and FIG. 16B, when the area AR2 that has been
encoded according to the CIRC7 system is read, although the reading
positions are fixed, the reading order is changed. For example, 59
reading positions have been designated. Whenever the area AR2 is
read, the reading order is changed. Although FIGS. 16A and B show
only two orders, there are many reading orders.
[0091] FIG. 17 shows an example using a semiconductor memory
(buffer memory). Whole data that is read from the area AR2 is
copied to the buffer memory. Thereafter, data is read from a
predetermined address of the buffer memory. The data is
error-corrected according to the CIRC4 system. Data D corresponding
to the error-corrected result is generated. Since the data of the
area AR2 has been stored in the buffer memory, the way that
encryption key data is generated cannot be seen from the outside.
As a result, the secrecy of the encryption key data can be
improved. Preferably, the buffer memory is tamper resistant.
[0092] In that example, as shown in FIG. 1 and FIG. 2, the optical
disc is a two-session optical disc, which is divided into an inner
periphery area and an outer periphery area where data according to
the CD-DA standard is recorded in one area and compressed audio
data is encrypted and recorded in the other area. However, as shown
in FIG. 18, of course, a one-session optical disc can be used.
[0093] In the example shown in FIG. 18, on the innermost periphery
of the optical disc, a first lead-in area LI is formed. On an outer
periphery of the area LI, a program area PA is formed. Outside the
program area PA, a lead-out area LO is formed. The program area is
divided into an area AR11 and an area A12. In the area AR11, data
is encrypted, encoded with an error correction code according to
the CIRC4 system, and recorded. In the area AR12, data is encoded
with an error correction code according to the CIRC7 system and
recorded. The data recorded in the area AR12 contains a data
pattern that can be corrected according to both the CIRC7 system
and the CIRC4 system.
[0094] FIG. 19 shows a recording apparatus according to an
embodiment of the present invention. For simplicity, according to
the embodiment, data is recorded to a one-session optical disc 62
as shown in FIG. 18. When the one-session optical disc 62 is a
read-only disc, a structure shown in FIG. 19 is applied as a
mastering system. In FIG. 19, content data to be recorded is
supplied to an input terminal denoted by reference numeral 51. An
example of the content data is audio data that has been compressed
according to the ATRA3. However, besides audio data, the present
invention can be applied to video data and music and video data.
Alternatively, content data that has been encrypted may be supplied
to the input terminal 51. Alternatively, part of the content data
may be encrypted.
[0095] The input data is supplied to a first input terminal of a
switch circuit 52. In addition, the input data is encrypted by an
encrypter 53 and then supplied to a second input terminal of the
switch circuit 52. The switch circuit 52 is controlled by a
controller (CPU) 54 that controls the whole recording apparatus. A
display, an operation switch, and so forth (not shown) are
connected to the controller 54. Depending on whether or not the
input data is to be encrypted, the switch circuit 52 is controlled
by the controller 54. Encryption key data (CIRC7-key) is supplied
from the controller 54 to the encrypter 53.
[0096] Output data of the switch circuit 52 is supplied to a CIRC4
encoder 55. The CIRC4 encoder 55 encodes the supplied data with an
error correction code according to the CIRC4 system. Output data of
the CIRC4 encoder 55 is supplied to a first input terminal of a
switch circuit 57. Output data of an encryption key (CIRC7 -key)
encoder 56 is supplied to a second input terminal of the switch
circuit 57. Data (including dummy data) that composes the
encryption key data or a part thereof that has been used in the
encrypter 53 is supplied from the controller 54 to the encryption
key encoder 56. In other words, the encryption key encoder 56
generates data recorded in the area AR2 encoded according to the
CIRC7 system (see FIGS. 12A, B, and so forth).
[0097] The CIRC4 encoder 55 dually performs an error correction
code encoding process for a C1 sequence (in the vertical direction)
and a C2 sequence (in the diagonal direction). When the error
correction code encoding process is performed according to the
CIRC4 system, the delay unit D is (D=4 frames) and the maximum
delay amount is 27 D (=108 frames). The encryption key encoder 56
dually performs an error correction code encoding process for the
C1 sequence (in the vertical direction) and the C2 sequence (in the
diagonal direction). When the error correction code encoding
process is performed corresponding to the CIRC7 system, the delay
unit D is (D=7 frames) and the maximum delay amount is 27 D (=189
frames).
[0098] The switch circuit 57 is controlled by the controller 54. In
the example shown in FIG. 18, the switch circuit 57 is controlled
by the controller 54 so that data encoded according to the CIRC4
system is recorded in the data track AR 1 and data encoded
according to the CIRC7 system is recorded in the data track AR2. As
was described above, to improve the secrecy of the encryption key
data, whenever data is recorded, when the positions of data that
can be corrected according to both the CIRC4 system and the CIRC7
system is changed, the controller 54 supplies data that has been
controlled in such a manner to the encryption key encoder 56.
[0099] Output data of the switch circuit 57 is supplied to a sub
code encoder 58. The controller 54 supplies sub code data to the
sub code encoder 58. The sub code encoder 58 adds a sub code to the
data supplied from the switch circuit 57 so as to convert the
supplied data into a predetermined record data format. Output data
of the sub code encoder 58 is EFM-modulated by an EFM modulator 59.
The EFM modulated data is supplied to a write storage portion 60.
The write storage portion 60 is a circuit that controls a data
recording method. The write storage portion 60 performs a process
for multiplex-recording for the area AR2, a process for changing a
track on which encryption key data is recorded, or the like.
[0100] An output of the write storage 60 is supplied to an optical
pickup 61. The optical pickup 61 outputs a laser beam that has been
modulated corresponding to the output data of the write storage 60.
The laser beam is radiated on a recording surface of the optical
disc 62. As a result, the data is recorded to the optical disc
62.
[0101] The optical disc 62 is held on a turn table and rotated by a
spindle motor 63. The spindle motor 63 is driven and rotated at
constant linear velocity (CLV) or constant angular velocity (CAV)
under the control of a servo portion 64. The servo portion 64
generates various types of servo drive signals such as focus servo
drive, tracking servo drive, and spindle servo drive corresponding
to a focus error signal and a tracking error signal supplied from
an RF portion 65 and an operation command supplied from the
controller 54 and outputs the generated signals to the optical
pickup 61 and the spindle motor 63.
[0102] The optical pickup 61 collects laser light as an optical
beam of a semiconductor laser as a light source to a signal surface
of the optical disc 62 with an objective lens and scans the signal
surface of the optical disc 62 so that tracks are formed in a
concentric circle shape or in a spiral shape on the optical disc
62. The objective lens of the optical pickup 61 is traveled in a
focus direction and a tracking direction by an actuator (not
shown). The whole optical pickup 61 can be traveled in a radius
direction of the optical disc 62 by a thread mechanism (not
shown).
[0103] FIG. 20 shows an example of a reproducing apparatus that
reproduces data from the forgoing optical disc 62. The optical disc
62 is held on a turn table and rotated by a spindle motor 71. The
spindle motor 71 is driven and rotated at constant linear velocity
(CLV) or constant angular velocity (CAV) under the control of a
servo portion 74.
[0104] The servo portion 74 generates various types of servo drive
signals of focus servo drive, tracking servo drive, and spindle
servo drive corresponding to a focus error signal, a tracking error
signal, and an operation command supplied from a controller 83 and
outputs the generated signals to the spindle motor 71 and an
optical pickup 72. The controller 83 controls the whole reproducing
apparatus. A display, an operation switch, and so forth (not shown)
are connected to the controller 83. The optical pickup 72 collects
laser light of a semiconductor laser as a light source on a signal
surface of the optical disc 62 and traces tracks formed in a
concentric circle shape or in a spiral shape on the optical disc
62. The whole optical pickup 72 is traveled in the radius direction
of the optical disc 62 by a thread mechanism (not shown).
[0105] An output signal of the optical pickup 72 is supplied to a
synchronization detector 75 through an RF amplifier 73. Output data
of the synchronization detector 75 is supplied to an EFM
demodulator 76. The demodulator 76 EFM-demodulates the data
supplied from the synchronization detector 75. Output data of the
demodulator 76 is supplied to a sub code decoder 77. The sub code
decoder 77 extracts sub code data from data supplied from the EFM
demodulator 76. Output data of the sub code decoder 77 is supplied
to a CIRC4 system error correction code decoding circuit
(hereinafter referred to as CIRC4 decoder) 78.
[0106] When data is reproduced from the optical disc 62, the
optical pickup 72 accesses a predetermined position of the optical
disc 62 and reproduces a part of the program area PA1. An output
signal of the optical pickup 72 is supplied to a CIRC4 decoder 78
through the RF amplifier 73, the synchronization detector 75, the
demodulator 76, and the sub code decoder 77.
[0107] The CIRC4 decoder 78 performs an error correcting process
according to the CIRC4 system. Output data of the CIRC4 decoder 78
is supplied to a switch circuit 79. The switch circuit 79 is
controlled by the controller 83. The reproduced content data that
has been encrypted is supplied to a decryptor 80. Reproduction data
of the area AR2 is supplied to a CIRC7 key extractor 81. The CIRC7
key extractor 81 generates encryption key data. The generated
encryption key data is supplied to the decryptor 80. The decryptor
80 decrypts the output data of the CIRC4 decoder 78. Reproduced
data is output to an output terminal 82.
[0108] TOC data and address data of the optical disc 62 are
supplied from the sub code decoder 77 to the controller 83. When
the optical disc shown in FIG. 1 is loaded to the reproducing
apparatus, the area PA2 is accessed. The optical pickup 72 reads
data from the program area PA2 and generates encryption key data.
Thereafter, content data of the program area PA2 is reproduced.
[0109] In the forgoing optical disc 62, in the area AR2, data that
has been encoded with an error correction code according to the
CIRC7 system contains data that can be corrected according to both
the CIRC4 system and the CIRC7 system. However, when this portion
is mistakenly reproduced as a sound, a uncomfortable sound will be
generated. Thus, in the data portion that can be corrected
according to both the CIRC4 system and the CIRC7 system, all high
order bits of the PCM signal are set to 0 or 1 so that the level of
the sound becomes low.
[0110] When a sound that is generated in a data portion that can be
corrected according to both the CIRC4 system and the CIRC7 system
is a direct current or a radio frequency wave, since the user
cannot easily recognize it, there is a risk of which he or she
turns up the volume. Thus, data 0s and data 1s will be buried in a
predetermined pattern so that an audible band sound is generated.
For example, data "0s" and data "1s" will be repeated at 7.35
kHz.
[0111] In some decoding circuit according to the CIRC system,
unless an error takes place in the C1 sequence, an error correction
process is not performed for the C2 sequence. For a process of a
drive or a player that has such a decoding circuit, in a part of
the area AR2, data that can be corrected according to both the
CIRC4 system and the CIRC7 system will contain an error of the C1
sequence.
[0112] The forgoing example describes the case that the present
invention is applied to a data recording medium. Besides the data
recording medium, the present invention can be applied to the case
that content data is encrypted and transmitted and encrypted data
is received. In other words, a predetermined period (frame, packet,
or the like) for data that is transmitted and received is a period
for data encoded according to the CIRC7 system. In the same manner
as described above, an encryption key can be buried in the data
period.
[0113] When the present invention is applied to data transmission
and reception, the structure of the recording system shown in FIG.
19 corresponds to the structure of the transmitting system. An
output of the switch circuit 57 is supplied to the transmitting
portion and transmitted to a wired or wireless communication path.
The structure of the reproducing system shown in FIG. 20
corresponds to the structure of the receiving system. The received
data is supplied to the RF amplifier 73. Data that has been
received and decrypted is obtained from the decryptor 80.
[0114] Although the present invention has been shown and described
with respect to a best mode embodiment thereof, it should be
understood by those skilled in the art that the foregoing and
various other changes, omissions, and additions in the form and
detail thereof may be made therein without departing from the
spirit and scope of the present invention. In the forgoing example,
data that can be corrected according to both the CIRC4 system and
the CIRC7 system was described. As long as the encoding structure
is the same, predetermined data that is repeated as one unit in the
vertical direction (C1 sequence) can be corrected regardless of the
interleave length.
[0115] In addition, besides the CIRC, data that can be corrected
according to a plurality of error correction systems can be
extended to another encoding system for performing an error
correction code encoding process according to two sequences. For
example, like the CIRC, using a product code with which an encoding
process is performed in the horizontal direction and the vertical
direction, data that can be corrected according to a plurality of
encoding systems can be considered.
[0116] According to the present invention, an optical disc as a
data recording medium has an area in which data is encoded with an
error correction code according to the CIRC7 system. In the area,
data that can be corrected according to both the CIRC4 system and
the CIRC7 system is recorded at a predetermined position in a
predetermined pattern. Since the data that can be corrected is used
as an encryption key or a part thereof, the secrecy of the
encryption key can be improved while the influence to a
conventional apparatus is reduced. In addition, when the structure
of the area and so forth are varied in various manners, the
encryption key can be kept more secret.
* * * * *