JP3527082B2 - Electronic authentication method and system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic authentication method and an electronic authentication system in which a distribution side adds specific information to an electronic image for distribution and the receiving side uses the specific information to evaluate the authenticity of the electronic image. Regarding

[0002]

2. Description of the Related Art In recent years, there have been increasing opportunities to distribute and receive various electronic images through an open network such as the Internet accessible by an unspecified number of users. However, in such an open network environment, since it is used by an unspecified number of people, it is assumed that the electronic image may be tampered with by a third party during distribution, and the recipient may not be aware of the tampering. In addition, although it has not been tampered with, it may be illegally copied and distributed. Therefore, an electronic authentication mechanism is required to check whether the delivered electronic image is the same as the one sent by the sender or whether the sender is a legitimate person on the receiving side. It

A conventional electronic authentication procedure is as shown in FIG. 7, in which a distribution side provides specific information created from an original electronic image, for example, a digest compressed by applying a hash function to the electronic image. Encrypt with the private key of the sender. Then, the original electronic image and the encrypted digest are delivered to the receiving side through the network.

On the receiving side, the electronic image received from the network is compressed with a hash function to create a digest, and the encrypted digest is decrypted with the sender's public key to obtain a digest. To decrypt. Then, the digest created from the original electronic image and the decoded digest are compared, and if both digests are the same, it can be determined that the electronic image is not a genuine electronic image, and if they are different, it is not a genuine electronic image. By the way, in the case of performing the electronic authentication as described above, it is necessary for the distribution side to distribute two types of data of the original electronic image and the encrypted digest to the reception side. Requires a separate data management means for the distribution side to appropriately manage which digest corresponds to which electronic image when distributing through a network.

As such data management means, conventionally,
Data hiding method, that is, for example, the copyright information of an electronic document is encrypted as a digest, and this digest is hidden in the original electronic image so that it cannot be visually recognized by human eyes, and this digest is used when necessary. A method of decoding and reading is adopted.

As a well-known technique that employs a method of embedding information in an electronic image, a technique that develops an electronic image in the frequency domain and processes a specific frequency component is shown (Reference: Nakamura, Ogawa, Takashima). : Digital watermarking method in the frequency domain for copyright protection of digital images, Th
e 1997 Symposium on Cryptography and InformationSe
curity-26A ”) and a method that directly processes the density value of each pixel that makes up an electronic image (reference“ Shimizu, Numao, Morimoto: still electronic image data high by pixel block ”). Ding, the technology disclosed in IPSJ 53rd National Convention 2-257 ”).

[0007]

By adopting the above-mentioned data hiding method, for example, the recipient can easily confirm the copyright information and the like from the electronic image distributed through the network. In addition to facilitating the management of the relationship with the digest, there is no need to separately display the copyright on the electronic image, so there is an advantage that the original electronic image can be kept as it is.

However, in the case of secretly embedding the encrypted digest in the electronic image using the above-mentioned data-handling method, the electronic image itself is changed due to the embedding of the encrypted digest. , Even if there is no tampering during distribution, the digest created from the electronic image before embedding the encrypted digest and the digest created on the receiving side from the electronic image after embedding will be significantly different,
In some cases, it may be difficult to properly perform electronic authentication.

That is, in the data handing method,
In general, for example, the digest is embedded using high-frequency components that are difficult for the human eye to understand, but since the bit string of an electronic image is calculated in byte units or word units to create the digest, digests are used for high-frequency components. The bit string of the electronic image changes before and after the embedding, and the created digest itself tends to change.

Therefore, an object of the present invention is to provide an improved electronic authentication method which enables accurate electronic authentication. Another object of the present invention is to provide an electronic authentication system suitable for implementing the above-mentioned electronic authentication method and its constituent devices.

[0011]

According to an electronic authentication method of the present invention for solving the above-mentioned problems, an electronic image including an aggregate of n pixels each represented by an m-bit density value as an element unit is converted into an electronic image of the electronic image. An information embedding process of creating specific information related to the content, encrypting the created specific information by a public key method and embedding it in the electronic image, and the specific information created from the electronic image in which the information is embedded and the electronic image And authenticating the electronic image by comparing and collating with the specific information obtained by decoding the obtained information. In the information embedding process, the upper mk bits of each pixel in the element unit are used to create the specific information, the created specific information is encrypted with the sender's secret key, and the encrypted information is n It is characterized in that the lower k bits of each pixel are embedded according to predetermined order information. Further, in the authentication process, the encrypted information obtained by reading the lower k bits of the pixel of the element unit in which the information is embedded according to the order information is decrypted with the sender's public key to reproduce the specific information. The reproduced specific information is compared and collated with the specific information created from the electronic image in which the information is embedded.

In the preferred embodiment, the order information is confidential information between the sender and the receiver, but may be information that follows a uniquely defined order in the structure of the element unit. Further, k is at least 1 bit, and it can be adjusted according to the density value and the number of pixels of the pixel in the element unit.

Further, in the electronic authentication system of the present invention which solves the above-mentioned other problems, a distribution device having an information embedding device and a receiving device having an information reading device are connected via a communication line, and the information embedding device is provided. The distribution image distributed from the distribution device through the distribution device and the communication line is received by the receiving device, and the authenticity of the distribution image is evaluated.

The information embedding device on the side of the distribution device reads the information from the electronic image in which the information encrypted by the public key system is embedded, decrypts the information, and evaluates the authenticity of the electronic image. An apparatus for generating delivery information addressed to an image, an image capturing means for capturing an electronic image including a set of n pixels each expressed by an m-bit density value as an element unit as a delivery image, and the delivery image. Information creating means for creating specific information relating to the contents of the image for distribution from the upper mk bits of each pixel in the element unit of, and encryption means for encrypting the created specific information with the sender's secret key. And a means for embedding the information encrypted by the encryption means in the lower k bits of each pixel of the element unit according to predetermined order information.

Further, the information reading device on the receiving device side is
An image capturing means for capturing the information-embedded distribution image from the information embedding device, and the lower k bits of the pixel of the element unit in which the information is embedded are read according to the order information to reconstruct the encrypted information. And means for decrypting the reconstructed encrypted information with the sender's public key to reproduce the specific information, wherein the reproduced specific information is created from the distribution image. It is characterized in that it is held as information for comparison and collation with specific information.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. (First Embodiment) FIG. 1 is a procedure explanatory view showing an embodiment of an electronic authentication method of the present invention, and is associated with the procedure of the conventional method shown in FIG. 5 for convenience. In this embodiment, the encrypted information, namely the cryptographic digest,
It is embedded in the electronic image and distributed to the network as follows.

That is, the higher mk bits of each pixel are used to create a digest from an electronic image that includes, as an element unit, a set of n pixels in which one pixel is represented by an m-bit density value. The digest is encrypted with the sender's private key to make an encrypted digest. Then, this cipher digest is embedded in the lower k bits of n pixels according to predetermined order information.

For example, when the density value of one pixel is represented by 8 bits, even if the least significant 1 bit representing each pixel is changed, the change cannot be recognized by human eyes, so that it is necessary to create a digest. Uses the upper 7 bits of 1 byte (8 bits) representing each pixel, and uses the lowest 1 bit of 1 byte to embed the cipher digest. on the other hand,
On the receiving side, the electronic image received via the network is compressed with a hash function to create a verification digest for the electronic image in which the encrypted digest is embedded, and at the same time, the lower k bits of the pixel of the element unit in which the information is embedded are The encrypted digest obtained by reading in accordance with the order information is decrypted with the sender's public key to reproduce the original digest. Then, the reproduced digest is compared and collated with the collation digest. The order information is confidential information defined between the sender and the receiver.

According to this method, the encrypted digest can be secretly embedded in the electronic image so that it cannot be visually recognized. Therefore, before and after the encrypted digest is embedded, electronic authentication can be performed without changing the electronic image with human eyes. become.

(Second Embodiment) Next, an electronic authentication system to which the above-described electronic authentication method is applied will be described. This electronic authentication system is configured to connect a distribution device and one or a plurality of receiving devices to a network, respectively, and perform electronic authentication using an encryption method based on a public key system. The distribution device includes the information embedding device of the present invention, and the receiving device includes the information reading device of the present invention.

FIG. 2 is a block diagram showing an example of the essential structure of this electronic authentication system. The information embedding device 100 included in the transmitting device has at least the following functions. (1) A function of capturing, as a distribution image, an electronic image including, as an element unit, a set of n pixels each represented by an m-bit density value. (2) A function of creating specific information related to the content of the distribution image from the upper m−k bits of individual pixels in the element unit of the distribution image. (3) A function of encrypting the created specific information with the sender's private key. (4) A function of embedding the encrypted information in the lower k bits of each pixel of each element according to predetermined order information.

In order to realize the above function, in the present embodiment, the image input unit 11, the electronic image storage unit 12, the data compression unit 13, the digest storage unit 14, the secret key storage unit 15,
Encryption processing unit 16, embedding processing unit 17, encryption storage unit 18,
Also, the information embedding device 100 is configured by including the image output unit 19. The information embedding device 100 can be realized by a general-purpose computer such as a personal computer or a workstation reading and executing a predetermined program recorded in a recording medium.

An example of the operation of the information embedding apparatus 100 when a document image of a gray scale bitmap format of 256 gradations in which one pixel is represented by 8 bits is targeted as a distribution image will be specifically described below. In this case, each pixel exhibits a density value of 0-255. That is, the density value "0" represents a white pixel, the density value "255" represents a black pixel, and the intermediate value thereof represents a gray pixel. That is, the greater the density value, the darker the gray color. Further, in the information embedding device 100, the upper 7 bits of 1 byte (8 bits) expressing each pixel are used for creating the digest as described above, and the lowest 1 bit of 1 byte is used for embedding the encrypted digest. Shall be used.

On the basis of the above assumptions, the image for distribution which is captured by the image input unit 11 and has 8 bits per pixel is stored in the image storage unit 1.
Save to 2. After that, the data compression unit 13 obtains a remainder obtained by dividing the upper 7 bits of the distribution image stored in the image storage unit 12 by a hash function, for example, the sum of the upper 7 bits of each pixel converted into a decimal number by 256. A digest is created by applying a function to perform data compression, and the digest is stored in the digest storage unit 14.

Next, in the encryption processing section 16, the digest stored in the digest storage section 14 is transferred to the secret key storage section 1
An encryption digest is generated by encryption with the sender's private key in No. 5, and this is stored in the encryption storage unit 18.

The embedding processing unit 17 embeds the encrypted digest in the least significant 1 bit of the pixel of the image for distribution stored in the image storage unit 12 according to predetermined order information, and sends this to the image output unit 19. In the image output unit 19, the distribution image in which the encrypted digest is embedded is sent to the network NW.
Deliver to. Note that the order information is preferably confidential information that has been negotiated between the sender and the receiver in advance, but if the order information is uniquely determined due to the structure of each element, the order may be followed.

The size of the cipher digest to be embedded may be adjusted according to the density value and the number of pixels of each element. That is, if the delivery image is a multi-gradation image image and deterioration of the image quality cannot be visually recognized even if a relatively large number of lower bits are used for the encryption digest, create a digest having a larger amount of information. So that it can be embedded.

The specific configuration of the information embedding device 100 is an example, and any other configuration may be used as long as it has the function described at the beginning. Next, the information reading device 200 included in the receiving device will be described.
The information reading device 200 has at least the following functions. (1) A function of capturing a distribution image in which information is embedded from the network NW. (2) Lower k of the element-unit pixel in which information is embedded
A function for reconstructing the cipher digest by reading the bits according to the above sequence information. (3) A function of decrypting this encrypted digest with the sender's public key and reproducing the original digest. (4) A function of retaining the reproduced digest as information for comparison and comparison with the comparison digest created from the distribution image.

In order to realize this function, in the present embodiment, the image input unit 21, the electronic image storage unit 22, the data compression unit 23, the digest storage unit 24, the cipher extraction unit 25, the cipher storage unit 26, the decryption processing unit. 27, public key storage unit 28,
The information reading device 200 includes the decrypted data storage unit 29, the difference determination unit 30, and the difference determination output unit 31. This information reading device 200 can be realized by a general-purpose computer such as a personal computer or a workstation reading and executing a predetermined program recorded in a recording medium.

The operation of the information reading device 200 is as follows. An image for distribution in which one pixel is 8-bit captured by the image input unit 21 (previous information embedding device 10
The encrypted digest is embedded by 0) is stored in the image storage unit 22. After that, the data compression unit 23 applies a hash function to the distribution image stored in the image storage unit 22 to compress the data, thereby creating a matching digest, and the matching digest is stored in the digest storage unit 24. To save.

Next, the cipher extractor 25 reads the cipher digest from the distribution image saved in the image accumulator 22 and stores it in the cipher accumulator 26. The decryption processing unit 27
The cryptographic digest stored in the cryptographic storage unit 26 is decrypted by the sender's public key in the public key storage unit 28 to reproduce the original digest, and the decrypted data storage unit 29 stores it.

The difference judgment unit 30 compares and verifies the collation digest stored in the digest storage unit 24 and the original digest stored in the decoded data storage unit 29, and the result information indicating whether they are the same or not. To the difference determination output unit 31. The specific configuration of the information reading device 200 is also an example, and any other configuration may be used as long as it has the function described at the beginning.

Next, the method of authentication by the electronic authentication system of this embodiment will be described in more detail with reference to FIGS. 3 and 4. 4 shows an example of the structure of data indicating the density value of one pixel by the information embedding device 100 of FIG. Figure 3
The data on the upper side of is “01111011”, which indicates the density value “123”. In this case, the upper 7 bits "0111101" are used to create the digest,
The least significant 1 bit “1” is used for embedding the encryption digest. The data on the lower side of FIG.
11 ”indicates the density value“ 255 ”. In this case as well, the upper 7 bits“ 1111111 ”are used for creating the digest, and the lower 1 bit“ 1 ”is used for embedding the encrypted digest. .

4 (a) and 4 (c) show the state transition before and after embedding the distribution image, and FIG. 4 (b) shows the embedding order information. Here, a distribution image in which the image is composed of 3 × 3 = 9 pixels and the data portion excluding the header portion is 9 bytes is targeted. Note that FIG. 4 (d)
Is the density value of each pixel before embedding the digest, (e) is the 8-bit data (bit string data) of the encrypted digest, and (f) is the density value of each pixel after the encrypted digest is embedded.

When embedding is performed when the 8-bit data of the cipher digest of FIG. 4E is "01001011", from the upper left pixel of 3 × 3 pixels to the right direction, and further from the left edge pixel of the second row to the right. 1-bit data is embedded in each pixel in order in the direction, and the check information (checksum bit) calculated from the bit string data “01001011” is embedded in the last lower right pixel. As the check information, it is possible to use, for example, information that is "0" if the sum of the bits of the bit string is even and "1" if it is odd. In this way, each pixel is represented by the density value of 256 gradations, and since it has 8-bit data,
Data embedding is performed by making the least significant bit of the 8-bit data of each pixel the same as the bit value to be embedded.

When such information embedding is performed, the change in the density value of each pixel to be converted before and after the embedding becomes the maximum of one least significant bit, and the difference cannot be discriminated by human eyes. . In addition, when a hash function is applied to perform data compression to create a digest, the top 7
Digest created by applying the hash function from the distribution image before embedding by using only bits and creating the digest and matching by creating the data compression by applying the hash function from the distribution image after embedding It is possible to make the digest the same. In the second embodiment, the digest is used as the specific information, but it goes without saying that other arbitrary information can be used.

[0037]

As is apparent from the above description, according to the present invention, there is a unique effect that electronic authentication can be performed with an image change that cannot be visually recognized by human eyes before and after embedding encrypted information. There is. Further, since the digests created from the distribution image before embedding the encrypted information and after the embedding can be made identical, there is an effect that appropriate electronic authentication can be performed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a procedure of an electronic authentication method of the present invention.

FIG. 2 is a block diagram showing a configuration example of a main part of an electronic authentication system of the present invention.

FIG. 3 is an explanatory view showing an example of a data structure showing a density value of one pixel used for information embedding in the electronic authentication system of the present invention.

4A and 4C are state transitions of a distribution image before and after embedding a cipher digest, FIG. 4B is embedding order information, and FIG. 4D is a density of each pixel before embedding a cipher digest. Value, the same (e) is the 8-bit data (bit string data) of the encryption digest, the same (f)
Is an explanatory view showing an example of the density value in each pixel after the encryption digest is embedded.

FIG. 5 is an explanatory diagram of a procedure of a conventional electronic authentication method.

[Explanation of symbols]

11,21 Image input section 12,22 Image storage unit 13,23 Data compression unit 14,24 Digest accumulation section 15 Private key storage 16 Encryption processing unit 17 Embedded processing section 18 Code storage 19 Image output section 25 Cipher Extractor 26 Code storage 27 Decryption processing unit 28 Public key storage 29 Decrypted data storage unit 30 Difference determination unit 31 Difference determination output section 100 Information embedding device 200 Information reading device NW network

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 1/387 H04N 1/40

Claims (7)

(57) [Claims] 1. Specific information relating to the content of the electronic image is created from an electronic image that includes, as an element unit, a set of n pixels each represented by an m-bit density value, and the created specific information is a public key method. The information embedding process that is encrypted by and embedded in the electronic image is compared with the specific information created from the electronic image in which the information is embedded and the specific information obtained by decrypting the information embedded in the electronic image. In the information embedding process, the upper mk bits of the individual pixels in the element unit are used to create the specific information, and the specific information is created. Is encrypted with the sender's private key and the encrypted information is embedded in the lower k bits of n pixels according to predetermined order information. 2. In the authentication step, the specified information is obtained by decrypting the encrypted information obtained by reading the lower k bits of the pixel of the element unit in which the information is embedded according to the order information with the sender's public key. 2. The electronic authentication method according to claim 1, wherein information is reproduced, and the reproduced specific information is compared and collated with specific information created from the electronic image in which the information is embedded. 3. The electronic authentication method according to claim 1, wherein the order information is secret information between a sender and a receiver. 4. The electronic authentication method according to claim 1, wherein the order information is information that follows a uniquely defined order in the structure of the element unit. 5. The electronic authentication according to claim 1, wherein the k is at least 1 bit and is variable according to the density value and the number of pixels of the pixel of the element unit. Method. 6. Each represented by an m-bit density value
Distribute electronic images that include a set of n pixels as an element unit
Image capturing means for capturing as an image for use, and for the delivery
Higher mk bits of each pixel in the image element unit
Create specific information related to the content of the image for distribution from
Information creation means and the created specific information is the sender's private key
Encryption means for encrypting with
Information stored in the lower k bits of each pixel in the element unit
And a means for embedding in accordance with predetermined order information, the public key
From the electronic image embedded with the information encrypted by the method
Read the information and decode it to evaluate the authenticity of the electronic image.
Image capturing means for capturing a distribution image with information embedded from an information embedding device for generating distribution information addressed to the receiving device , and lower order k bits of the pixel of the element unit with information embedded, the order information And a decryption unit for decrypting the reconfigured encrypted information with the sender's public key to reproduce the specific information. An information reading device, which holds the reproduced specific information as information for comparison and collation with specific information created from the image for distribution. 7. Each is represented by a density value of m bits.
Distribute electronic images that include a set of n pixels as an element unit
Image capturing means for capturing as an image for use, and for the delivery
Higher mk bits of each pixel in the image element unit
Create specific information related to the content of the image for distribution from
Information creation means and the created specific information is the sender's private key
Encryption means for encrypting with
Information stored in the lower k bits of each pixel in the element unit
And a means for embedding in accordance with predetermined order information, the public key
From the electronic image embedded with the information encrypted by the method
Read the information and decode it to evaluate the authenticity of the electronic image.
A distribution device comprising an information embedding device for generating distribution information addressed to the reception device, and a reception device comprising the information reading device according to claim 6 are connected via a communication line. An electronic authentication system, wherein the receiving device receives the distribution image distributed from the embedded device through the distribution device and the communication line, and evaluates the authenticity of the distribution image.