JP2001203879A - Method and device for electronic watermark and recording medium with stored processing program therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a center for embedding electronic watermarks from unauthorized distributing a digital work. SOLUTION: The holder of the digital work inputs the digital work to a holder device 10, enciphers that work with a cryptographic key, while using an enciphering means 13 and transmits the enciphered digital work to a center 20. The center 20 embeds an electronic watermark to the received enciphered digital work and sends the enciphered digital work embedded with that electronic watermark to the holder device 10. The holder device 10 deciphers the received information with the cryptographic key, while using a deciphering means 15 and provides information directly embedding the electronic watermark in the digital work.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital watermarking method used for copyright protection in the distribution of digital works, an apparatus therefor, and a program recording medium therefor.

[0002]

2. Description of the Related Art When considering distribution of digital works, copyright protection is considered to be a major problem. Conventionally, in order to solve this problem, a copyright protection system using digital watermarking technology (Takao Nakamura, Hiroshi Ogawa, Yoichi Takashima: "Copyright protection method and system", Japanese Patent Application No. 8-305370 (1996), etc.) has been proposed. Proposed. Digital watermarking technology
If information such as the algorithm and parameters becomes apparent, there is a security (security) problem. Therefore, it is desirable to embed / detect an electronic watermark only in a limited place. for that reason,
For example, (Takao Nakamura, Hiroshi Ogawa, Yoichi Takashima: “Copyright Protection Method and System”, Japanese Patent Application No. 8-305370 (199)
In 6)), etc., only the center has the functions of embedding and reading digital watermarks, and the author who has created the digital work sends the digital work created by himself to the center and returns it after embedding the digital watermark. It was necessary to take steps such as receiving

In this method, however, the author must send the digital work itself created to the center, and the center can illegally distribute the obtained digital work.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to prevent the center from obtaining the work itself sent from the author in order to prevent the center from being fraudulent, which was impossible with the prior art. Another object of the present invention is to provide a digital watermarking method, a device thereof, and a program recording medium for enabling more secure copyright protection.

[0005]

In order to achieve the above object, according to the digital watermarking method of the present invention, when a person who owns a digital work requests a center to embed a digital watermark in the digital work, Then, the digital work is encrypted and sent to the center. The center that has received the encrypted digital work performs a digital watermark embedding process on the digital work in the state of being encrypted, and returns the embedded encrypted digital work to the owner.

[0006] Lastly, the owner who has received the embedded encrypted digital work performs a decryption process to obtain the embedded digital work.

[0007]

According to the present invention, since the owner of a work encrypts his digital work and sends it to the center to request the embedding of a digital watermark, the center cannot obtain the digital work itself. In addition, unauthorized distribution of digital works by the center can be prevented, and the owner can request the center to embed a digital watermark with confidence.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a digital watermark system according to an embodiment of the present invention. This system comprises an owner device 10 and a center device 20. The owner holds a digital work in, for example, a storage means, and the owner requests the center to embed a digital watermark in the digital work. First, the digital work is input to the owner device 10 by the input unit 11, and an encryption key used in this request is created by the encryption key generation unit 12, and the data is input by the data encryption unit 13 using the encryption key. The digital work from the means 11 is converted into an encrypted digital work, and the encrypted digital work is sent to the center device 20 by the transmission means 14.

The center device 20 receives the encrypted digital work sent from the owner device 10, and performs digital watermark embedding processing on the received encrypted digital work by using the digital watermark embedding means 21. An encrypted digital work with a digital watermark embedded therein is generated, and the encrypted digital work with the digital watermark embedded is sent to the owner device 10 by the transmission unit 22. The owner device 10 decodes the digital watermark-embedded encrypted digital work sent from the center device 20 by using the data decoding unit 15 to obtain the digital watermark-embedded digital work, and the generation unit 16 outputs the digital work with the external watermark embedded. Store in storage means.

[0010] Thereafter, the owner distributes the digital work in which the digital watermark is embedded, as usual, and implements the copyright protection by using the normal copyright protection function using the digital watermark. An example of a key generation method by the encryption key generation unit 12 in the above embodiment will be described with reference to FIG. The number of samples of the digital work to be encrypted is assumed to be N as shown in FIG. 2A, and the range of possible values of each sample s _i (0 < i <N) is assumed to be 0 < s _i <k. For example, for audio data having a sampling rate of 16 bits (one sample is 16 bits), k = 65536, and for grayscale image data having 8 bits per pixel, k = 256. In this case the encryption key is _{{r i} (0 <i} <N, 0 <r i <k + 2m) ( where m is the maximum number greater than the absolute value of the change amount of the sample that can take the electronic watermark embedding means) It is generated as a random number sequence such that That is, the encryption key is a random number sequence having the same length as the number of samples of the digital work, and the range of possible values is the range of possible values of the sample of the digital work, and the width over which the sample can be changed by the digital watermark. The margin is expanded by twice the larger margin.

At this time, if possible, instead of using a pseudo-random number generator or the like to generate an encryption key, thermal noise of electric resistance due to a quantum effect or a time interval of a key input by a user (generation of random numbers by this method) The program is public)
It is desirable to use a random number that is not determined deterministically, that is, a true random number. This is because when a true random number is used, a data encryption unit 13 described later can be a completely secure encryption generally called a Vernam encryption, and the security level of the system is improved.

FIG. 3 shows an example of the processing flow of the encryption means 13 in the above embodiment. Encrypting means 13 receives the digital work s _i and the encryption key r _i. First, i is initialized to 0 (S1), and an encrypted digital work {e _i } (0 < i <N) output from the encryption means 13 is obtained as follows (S2). _{e i ← s i + m +} r i (mod (k + 2m)) (0 <i <
N) where mod x is a symbol representing an operation with a coset modulo x.

Next, i is incremented by 1 (S3), and it is checked whether i is smaller than N (S4). If i is smaller, the process returns to step S2.
If not, the process ends. The digital watermark embedding means 21 in the above embodiment will be described below. In the digital watermarking system according to the present invention, it is essential that the following properties are established between the above-described encryption means 13, digital watermark embedding means 21, and decryption means 15 described below: E (•): Encryption process D (•): decryption process W (•): digital watermark embedding process C: digital work D (W (E (C))) = W (C) (1) That is, A digital work E (C) in which a digital watermark is embedded and a digital work W (E (C)) in which the digital watermark is embedded is decrypted as a result.
Digital work with digital watermark embedded directly W
This is a property that is equivalent to (C).

Assuming the encryption method described above, a digital watermark satisfying this property may be any method that adds / subtracts a value determined by a method independent of the sample value. Here, the following simple method is exemplified: {p _i }: random number sequence (−m <p <m, 0 < i <N) a: digital watermark information If, Is W (s _i ) = s _i + p _{(i + a)% N} (0 < i <N). Here, a% b is a symbol representing a remainder when a is divided by b. If W (s _i ) <0, W (s _i ) =
If 0, W (s _i ) > k, rounding of values is performed such that W (s _i ) = k−1.

FIG. 4 shows an example of the processing flow of the processing 21 of the digital watermark embedding means 21 in the above embodiment based on the above points. The input of the digital watermark embedding means 21 is the encrypted digital work e _i and the digital watermark information a, and the output is the digital watermark embedded encrypted digital work z _i . In addition, digital watermark information may be provided from the outside depending on how to use the digital watermark. For example, there is a case where digital watermark information is sent from the owner device 10 together with the encrypted digital work and the digital watermark information is embedded in the center device 20.
Alternatively, a value such as a serial number may be generated by the center device 20 and may be used as an input for the digital watermark embedding process. First, a random number sequence {p _i } is generated (S1), and i is initialized to 0 (S2). Next, the encrypted digital work {z _i } (0 < i <N) embedded with the digital watermark is obtained as follows (S3): z _i ← e _i + p _{(i + a)% N} (mod (k + 2m) )) (0 < i
<N) Since the function is slightly different from W (•) described earlier because of the addition of the modulo, this function is represented as W ′ (•), but essentially the same is done. In this case, D (W '(E (C))) = W (C) (2) should be satisfied in a form corresponding to the expression (1). Satisfying this property is stated last.

Next, i is incremented by 1 (S4), and it is checked whether i is smaller than N (S5). If i is smaller, the process returns to step S3.
If not, the process ends. In addition, the digital watermarking method is not limited to the method described here, and for example, (Takao Nakamura, Hiroshi Ogawa,
Atsushi Tomioka, Yoichi Takashima: "Digital watermark embedding method, digital watermark detecting method, digital watermark embedding device, digital watermark detecting device, storage medium storing digital watermark embedding program, and storage medium storing digital watermark detecting program And Japanese Patent Application No. 11-16219 (199
9)) and (W. Bender, D. Gruhl, N. Morimoto, A. Lu:
“Techniques for data hiding”, IBM Systems Jou
rnal, vol. 35, no. 3 & 4, pp. 313-336, (1996)) and various other methods can be used.

The processing of the decoding means 15 in the above embodiment
An example of the flow is shown in FIG. The decoding means 15 embeds a digital watermark
Embedded encrypted digital work z_iAnd the encryption key r _iEnter
And a digital work w with digital watermark embedded_iOutput
And First, i is initialized to 0 and the digital watermark is embedded
Digital work @ w_i｝ (0<i <N) is as follows
Then ask:Next, i is incremented by 1 and the above step is repeated until i becomes N-1.
1. ~ 3. , For i = 0, 1,..., N−1.

Now, the above-mentioned encryption processing and digital watermark embedding
It is shown below that the processing and decryption satisfy the property of equation (2).
Shown in: z_i= E_i+ P_{(i + a)% N}= S_i+ M + r_i+ P
_{(i + a)% N}Therefore, step 1. smell
And w_i← z_i-R_i= S_i+ M + p_{(i + a)% N} (Mod (k +
2m)). After this, step 2. At w_i← w_i−m = s_i+ P_{(i + a)% N} Becomes At this time -m<w_i<K + m
In step 3. The result of rounding with_i)
Becomes equal to That is, D (W '(E (C))) = W (C) where C is a digital
This is illustrated in FIG. 6 as shown in FIG. First
(A) s_iAnd r in (b) _iApply encryption means 13 to
Then, e of (c)_iIs obtained. Here, in FIG.
The value wrapped at k + 2m to make the operation easier to understand,
S_i+ M + r_iE minus k + 2m_iage
Is shown. Next, in (d), the digital watermark is embedded.
By means 21_iTo p_{(i + a)% N}Is added to z_iTo
obtain. Further, step 1. And z_iFrom
r_iIs subtracted from w in (e)._iIs obtained. At this time
A rectangular part filled with diagonal lines, that is, p_{(i + a)% N}Haso
Does not exceed m, w in FIG._i
Does not exceed k + 2m. Finally, the decoding means st
ep2. And step 3. By w_iLike
The child is shown in FIG. In w_iFrom m
W remaining after subtracting_iIs step 3. Fly over k
The protruding part (broken line part) is rounded. this
(F) is a direct digital watermarking method for digital works.
Represents the state at the time of applying. Also embedding digital watermark
By means 21_iAlso jumps in the negative direction
Similarly, it is rounded to zero. From the above, the cipher of this embodiment
Means 13, digital watermark embedding means 21, decoding means 1
It is found that the processing by 5 satisfies the property of the expression (2).
Was.

Finally, the detection means for detecting a digital watermark in this embodiment will be described with reference to FIG. The example of the digital watermarking method of this embodiment is basically a digital watermark applying a spread spectrum communication method. The detection method is as follows: First, a random number sequence {p _i } is prepared, j is initialized to 0 (S1), c _j is initialized to 0 (S2), and i is initialized to 0. after (S3), and calculates the _{c j + w i · p (} i + j)% N, the result was a c _j (S4), the i and +1 (S5), i is checked whether N is less than (S6 ), If smaller, return to step S4; if smaller, j is incremented by 1 (S7); check if j is smaller than N (S8); if smaller, return to step S2; if smaller, set the maximum value of {c _j } to J at the time of taking is output as electronic information a (S
9).

That is, j = 0 ... N-1

[0021]

(Equation 1) Is obtained, and j at the time of taking max {c _j } is output as digital watermark information a. The above processing is an operation for obtaining a correlation value with a digital work with a digital watermark embedded therein while shifting the start term of the sequence one by one based on the spread sequence {p _i }. When it matches the shift amount a at the time of embedding, a peak appears in the correlation value, and the digital watermark is successfully detected.

If it is desired to embed a larger amount of information or to achieve resistance to compression, etc. (Takao Nakamura, Hiroshi Ogawa, Junki Tomioka, Yoichi Takashima: "Electronic watermark embedding method and electronic watermark detection method" And a digital watermark embedding device, a digital watermark detecting device, a storage medium storing a digital watermark embedding program, and a storage medium storing a digital watermark detecting program, "
1-116219 (1999)) and (W. Bender, D. Gruhl,
N.Morimoto, A.Lu: “Techniques for datahidin
g ”, IBM Systems Journal, vol.35, no.3 & 4, pp.3
13-336, (1996)).

Also, other encryption methods and digital watermarking methods than those shown in the above embodiments can be applied to the digital watermarking method of the present invention as long as the properties of the equations (1) and (2) are satisfied. . In addition to the equations (1) and (2), if there is a function X (•) that also satisfies the following properties, the digital watermarking system of the present invention can be realized using the function X (·): D (X (E (C))) = Z, and when the digital watermark detection function (paired with the digital watermark embedding function W (•)) is Y (•), Y (Z) = Y (W ( C)) A function X (•) that satisfies

That is, Z ≠ W (C) may be satisfied (however, Z
And W (C) (and C) can be identified in human perception,
Is necessary). As a digital watermark, when using a method of orthogonally transforming a sample value and embedding it in an area converted into another expression method such as a frequency space, by using the sample value of the encrypted digital work as each component value of the conversion area, Can be easily realized.

[0025]

As described above, according to the present invention,
Since the owner of a digital work encrypts the digital work and sends it to the center to request the embedding of a digital watermark, the center cannot obtain the digital work itself, preventing the center from illegally distributing the digital work. The owner can request the center to embed a digital watermark with peace of mind.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a functional configuration of a digital watermark system according to an embodiment of the present invention.

FIG. 2 is a view for explaining an encryption key generation method in the embodiment.

FIG. 3 is a diagram showing a flow of processing of an encryption unit 13 in the embodiment.

FIG. 4 is a digital watermark embedding unit 2 in the embodiment.
The figure which shows the flow of 1 processing.

FIG. 5 is a view showing a flow of processing of a decoding unit 15 in the embodiment.

FIG. 6 is a view schematically showing an image of a process in the embodiment.

FIG. 7 is a view showing a flow of processing of a digital watermark detection unit in the embodiment.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) 9A001 (72) Inventor Yoichi Takashima 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Kanade Yamamoto 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Riki Horioka 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Stock Company F term (reference) 5B017 AA06 BA07 BB02 CA16 5B057 AA11 CE08 CG01 5C076 AA14 BA09 5C078 AA04 CA47 DA01 DA02 5J104 AA14 9A001 EE02 EE03 GG22 KK60 LL03

Claims (16)

[Claims] 1. A digital watermarking method in which a person who owns a digital work sends a digital work to a center that embeds a digital watermark and requests the center to embed the digital watermark. The owner device encrypts the digital work, sends the encrypted digital work to the center device, and the center device embeds a digital watermark in the received encrypted digital work, The encrypted digital work having the watermark embedded therein is sent to the owner device, and the owner device decodes the received encrypted digital work having the digital watermark embedded therein, and detects a digital watermark with respect to information obtained as a result of the decoding. As a result of digital watermarking, a digital work with an embedded digital watermark Watermarking method is characterized in that to be able to obtain a result equivalent information were detected Luo watermark. 2. The process of encryption, the process of embedding the digital watermark, and the process of decryption are performed by directly applying a digital watermark to the digital work, and encrypting the digital work by the encryption. 2. The information obtained by embedding the digital watermark in the digital watermark embedding process with respect to the information encrypted in the process and the result obtained by further decoding in the decoding process match. Digital watermarking method. 3. The process of encryption, the process of embedding the digital watermark, the process of decryption, and the process of detecting the digital watermark are results of directly embedding the digital watermark in the digital work. The information obtained by embedding the digital watermark in the digital watermark embedding process for the information obtained by encrypting the digital work in the encryption process and the result obtained by further decoding in the decryption process match. However, the result of performing the digital watermark detection process on the information obtained by embedding the digital watermark in the digital work and the information obtained by encrypting the digital work by the encryption process are compared with the digital watermark. The information obtained by embedding the digital watermark by embedding is further obtained by performing the digital watermark detection process on the information obtained by decoding by the above decoding process. 2. The digital watermarking method according to claim 1, wherein the results match. 4. The method according to claim 1, wherein the encryption processing and the decryption processing are based on addition and subtraction on a coset modulo a certain number. Digital watermarking method described in 1. 5. The digital watermarking method according to claim 1, wherein the digital watermark processing changes each sample value independently of a value of each sample of the digital work. . 6. The encryption processing is assumed to be the same length as the number of samples of the digital work and within a range of values that can be taken by each sample of the digital work, and further by the digital watermark processing. A random number sequence is generated such that a value obtained by adding twice a value larger than the maximum value of the absolute value of the amount of change of each sample value to obtain a range of possible values of each term is obtained. The value obtained by dividing the sample value by adding the corresponding term of the random number sequence to a range of possible values of each term of the random number sequence is used as a value of each sample to obtain the encrypted digital work as a value of each sample. The digital watermarking method according to claim 4, wherein the digital watermark is obtained. 7. The decoding process according to claim 1, wherein a result obtained by subtracting a corresponding term of the random number sequence from each term of the digital watermark embedded encrypted digital work is a range of possible values of each term of the random number sequence. Is obtained by subtracting a value larger than the maximum value of the absolute value of the amount of change of each sample value that can be assumed by the digital watermarking process from the value of the remainder, and further calculating If the result of the operation exceeds the range of possible values of the sample of the digital work, the value obtained by performing the rounding process so that the value falls within the range of the possible value of the sample of the digital work is calculated as 7. The digital watermarking method according to claim 6, wherein the digital work in which the digital watermark is embedded is obtained as a sample value. 8. The process of generating the random number sequence is not a deterministic sequence such as a pseudo-random number but a true random number sequence that cannot be reproduced, such as thermal noise due to quantum effects and input intervals at key input. 8. A digital watermarking method according to claim 6, wherein 9. An encryption means for inputting a digital work and an encryption key to output an encrypted digital work, a means for transmitting the encrypted digital work to a center device, Means for receiving the processed information and the encryption key and performing a decoding process to output information in which a digital watermark is embedded in the digital work. Digital watermarking device. 10. The digital watermark apparatus according to claim 9, further comprising an encryption key generating means for generating a true random number as said encryption key. 11. A means for receiving an encrypted digital work from a device of an owner of the work, and a cryptographic apparatus in which the encrypted digital work and a digital watermark are input and the digital watermark is embedded. A digital watermark embedding unit that outputs a digitalized digital work, and a unit that transmits an encrypted digital work in which the digital watermark is embedded to a device of the owner of the work. 12. The digital watermarking apparatus according to claim 11, wherein said digital watermark embedding means is means for changing a sample value of the encrypted digital work in accordance with the digital watermark. . 13. A process for inputting a digital work, a process for encrypting the input digital work with an encryption key, a process for transmitting the encrypted digital work to a center device, A recording medium storing a program for causing a computer of a digital watermark device to execute a process of receiving information processed from a device and a process of decoding the received processed information with the encryption key. 14. A recording medium comprising a program for causing the computer to execute a process of generating a true random number as the encryption key used in the encryption process and the decryption process. 15. A process for receiving an encrypted digital work from a device of the owner of the work, a process for embedding a digital watermark in the received encrypted digital work, Encrypted digital works with embedded watermarks,
A recording medium storing a program for causing a computer of a center device to execute the process of transmitting the copyrighted work to the device of the owner. 16. The recording medium according to claim 15, wherein the process of embedding the digital watermark is a process of changing a sample value of the encrypted digital work in accordance with the digital watermark.