KR20120055070A

KR20120055070A - System and method for lossless digital watermarking for image integrity

Info

Publication number: KR20120055070A
Application number: KR1020100116572A
Authority: KR
Inventors: 유길상
Original assignee: 유길상
Priority date: 2010-11-23
Filing date: 2010-11-23
Publication date: 2012-05-31

Abstract

PURPOSE: A lossless digital watermarking system and a method thereof are provided to verify the integrity of an image and recover an original image when a watermark is extracted. CONSTITUTION: An image insertion unit initializer(110) initializes a least significant bit of an insertion target image. A watermark generator(120) generates pseudo sequence used as a watermark. A hash function calculator(130) obtains a hash function result value. A watermark insertion unit(40) finally inserts the watermark into the image by an XOR function.

Description

System and Method for lossless digital watermarking for image integrity

The present invention uses a method of embedding a watermark with embedding and distortion to generate a recoverable image data signal, and receiving reconstruction data to reconstruct the original image signal. The present invention relates to a method of inserting auxiliary data into an original image signal. The invention also relates to a corresponding apparatus for embedding a watermark signal in an original video signal.

The present invention relates to a method for reconstructing and reconstructing a watermarked original video signal by 100%, and a composite video information signal for extracting embedded data.

The purpose of authentication and integrity of digital images is to identify the creator of the content and to verify that the content of the content has not been altered or tampered with. In addition, if the content has been modified, it is necessary to identify where the modification has been made. The method of checking whether the image is deformed (manipulated) is a digital signature and a watermarking system. The watermarking system has a problem of slightly damaging the image, but since the watermark is directly inserted into the image, there is no need to store additional data. Digital Signature does not use the unique structure of the image because it regards the image as a simple data sequence, but the watermarking system can take advantage of the structural characteristics of the image so that the position and the type of modulation in the image space can be known.

There are many ways to ensure the authentication and integrity of an image.

The following shows various methods for authentication and integrity.

Wong proposed a method using MD5, a cryptographic hash function (P. W. Wong, "A watermark for image integrity and ownership verification," In Proceedings of IS & T PIC Conference, May 1998). First, the image is divided into blocks of I * J pixel size. (I * J <128) Then the LSB (least significant bit) portion of each block is removed. This creates a digital signature by passing the remaining significant bits (MSBs), the size of the image, and the secret-key through a cryptographic hash function. The generated signature is combined with the watermark image to be inserted through the XOR operation and inserted into the LSB portion of the image block. The process of extracting a watermark from the watermarked image first divides the image into blocks of size I * J pixels. Then, each block's MSBs, image size, and secret key are used to create a digital signature. Then, the LSB of the block and the digital signature and XOR operation obtained earlier will display the first inserted watermark image. Wong's algorithm first inserts a watermark in the image using A's secret key. If B wants to verify the authenticity and integrity, he can extract the correct watermark image using the correct private key. However, if B tries to check the watermark using the wrong key, or if the image is enlarged or only partially cropped, noise will appear instead of the watermark image. Also, when a part of the image pixel is changed, it is possible to check which part of the pixel has changed.

Wong extended the previous watermarking algorithm to apply public key encryption algorithms (P. W. Wong, "A public key watermark for image verification and authentication," In Proceedings of ICIP, Oct. 1998). In other words, the user's private key is used to insert the watermark, and the person's public key is used to extract the watermark. This method is similar to the previous method. First, the image is divided into blocks having a specific size (I * J). In each block, the LSB of each image pixel is deleted, and a digital signature can be obtained by passing the hash function using the remaining portion of the MSBs and the size information of the image. It then encrypts this signature with the user's private key and performs an XOR operation with the image you want to insert as a watermark. Then reinsert it into the LSB portion of the image block. Wong's public key watermark method using public key cryptographic algorithm is the most suitable watermark method for authentication and integrity. In particular, Wong's method uses cryptographic hash functions, so the security of the watermarking algorithm depends on the security of the cryptographic hash functions. However, one of the characteristics of cryptographic hash function is that it is very difficult to break cryptographic hash function, so the method proposed by Wong is safe. Wong's proposed algorithm has two problems. The problem that results from many watermarking and data-hiding schemes is that the original video signal into which the watermark data is inserted is distorted.

Sources of distortion include rounding errors, rounding errors, and quantization errors. This distortion is problematic in some applications, such as media analysis and law enforcement, because it is important to accurately restore the original image to its pre-insertion state as soon as the hidden data is retrieved. Watermarking techniques that meet this requirement are referred to as lossless or distortion free.

Integrity verification and lossless watermarking are efficient for integrity verification because they are a method of restoring the original in the future, unlike watermarking that damages the original. In the case of medical images, if the image reading is performed without reconstructing the original image with integrity verification, it can probablely cause the wrong care of the reader. In the present invention, when the watermark is inserted and the watermark is extracted using a lossless technique, the original image can be restored at the same time as the integrity verification.

In order to achieve the above object, a method for embedding a lossless digital watermark for integrity authentication of a digital image according to the present invention includes converting an input image into a predetermined block;

Dividing the least significant bit values representing the characteristics of the input image and a watermarking block into which a watermark is to be inserted;

Calculating the LSB region of the input image by MD5 hash function value and XOR operation;

Generating a pseudo noise sequence using a private secret key and inserting the pseudo noise sequence into the hash function result value and the input image;

And inserting the feature value into the watermarking block as a watermark.

In addition, a method for extracting a lossless digital watermark for authenticating the integrity of a digital image according to the present invention comprises: dividing an input image into predetermined blocks;

Extracting least significant bits from the divided input image;

Dividing the input image into a predetermined size based on the extracted least significant bit;

And determining the integrity and the forgery of the input image according to the difference between the pseudo sequence value generated as the secret key value and the feature value in the watermarking block.

Hereinafter, a method of inserting and extracting a digital watermark for authenticating a digital image according to the present invention will be described in detail with reference to the accompanying drawings.

The process of embedding the watermark includes image initialization unit 110 for initializing the least significant bit of an image to be largely inserted, watermark generation unit 120 for generating a pseudo sequence to be used as a watermark, calculation of least significant bit and hash function of the image. The hash function calculation unit 130 for inserting the result value and the watermark is processed by the watermark inserting unit 140 in which the watermark is finally inserted by the XOR function.

The least significant bit of the image to be used as the input of FIG. 4 is divided into 16 * 8 pixel forms (110) and all LSB values are initialized to zero. In the watermark generator 120, a pseudo sequence having only a configuration value of 0 and 1 is generated by a secret key and used as a watermark. The hash function calculation unit 130 performs hash function processing with each block value of the image and outputs the hash function. The value output from the watermark generator 120 and the hash function calculator 130 is inserted into the watermark 140 by an XOR operation. The watermark inserting unit 140 is processed by XOR operation to verify the integrity of the image and recover the original image. The image generated by the watermark inserting unit 140 satisfies 50.27dB of invisibility as shown in FIG. 5.

The watermark extraction process is performed through the extraction information calculation unit 210 from the watermarked image. In order to confirm the integrity of the image, a collation watermark is generated using a secret key value used in the watermark generator 120 of the watermark embedding step. The integrity verification unit 230 compares the watermark and the watermark information extracted by the watermark extraction calculation unit 210 and performs integrity verification. An image without forgery from the watermarked image may obtain an inserted watermark as shown in FIG. 6. If the image is forged as shown in FIG. 7, the position of the forgery can be checked as shown in FIG. 8 through the difference between the two bits. If the integrity is verified, the same image as the original image from which the watermark is removed can be obtained through the image restoring unit 240 as shown in the image of FIG. 9.

Conventional fragile watermarking has been used to discriminate forgery of an image, but it does not reconstruct the original image at the same time as watermark extraction. The present invention can be used for the authentication and reconstruction of the sensitive image that can cause a huge loss even in small changes such as military image or medical image by solving the disadvantage of the existing soft soft watermarking.

For the purpose of illustrating various aspects of the invention, drawings illustrating preferred embodiments of the invention are shown, but are not limited to the means shown and the precise arrangement.
1 is a flowchart schematically illustrating a process of inserting, verifying, and recovering a digital watermark for a lossless digital watermarking system and method capable of verifying and restoring an integrity of an image according to the present invention.
2 is a flowchart schematically illustrating a process of inserting a watermark generator and generated feature values as watermark information.
3 is a block diagram schematically illustrating a calculation unit for extracting a watermark, and an integrity verification and restoration process.
4 is a photograph showing an example of an image performed in a watermarking test, which is an example of an image (original image) having a size of 512 * 512 pixels.
FIG. 5 illustrates an image after watermarking the image of FIG. 4.
6 is a graph showing the correlation degree NC between the extracted watermark and the inserted watermark.
FIG. 7 is an image of artificially modulating FIG. 4.
FIG. 8 is a diagram illustrating a difference of pixel difference values between an original image and the modulated image of FIG. 7 by an algorithm.
9 illustrates an image restored to an original image after authentication of forgery by an algorithm.

Claims

A method of embedding a digital watermark for integrity authentication and lossless restoration of a digital image, the method comprising: converting an input image into a predetermined block;
Calculating an LSB region of the input image as an MD5 hash function value;
Generating a watermark formed of a pseudo noise sequence;
Dividing the input image into a LSB block and a witter marking block into which a watermark is to be inserted;
Embedding the feature value as a watermark in the watermarking block.

The method of claim 1,
And converting the input image into a predetermined block.

The method of claim 1,
Generating the watermark
Generating a pseudonoise sequence using a predetermined secret key; And
And sequentially inserting the generated watermark with respect to the entire area of the input image.

The method of claim 3, wherein
And inserting a digital watermark by modulating the least significant bit of an image into a hash function and an XOR operation to allow lossless recovery of the generated watermark sequence.

The method of claim 4, wherein
Inserting the final watermark is
And XOR conversion of the LSB value, the hash function value, and the binary sequence value.

The method of claim 5, wherein
Inserting a bit value into the block by modifying the pixel value of the pixels using a logical one bit difference value.

The method according to claim 6,
Hiding the inserted bit value in the block of the image to be reconstructible.

In the method for extracting the digital watermark inserted according to claim 1, 2, 3, 4, 5, 6 or 7 for the authentication of forgery of the digital image,
Converting the input image into a predetermined block;
Extracting a least significant bit value from the input image;
Generating a pseudo sequence from a predetermined secret key;
Extracting a watermark from the extracted LSB value;
And determining whether the input image is forged or altered according to the magnitude of the difference between the extracted value LSB and the feature value in the pseudo queen block.

The method of claim 8,
And calculating a degree of correlation between the added input image and the watermark bit to extract a watermark from a calculated value to determine the integrity of the digital watermark.

The method of claim 8,
Extract the inserted bit value using the block difference value,
And extracting a logical one-bit sequence from the block difference value, and restoring the pixel value to a state of the pixel value before being changed from the extracted bit value to the inserted bit value. Data extraction method and extraction device.

A computer-readable recording medium having recorded thereon a program for performing an operation by the method of inserting a digital watermark according to claim 1, 2, 3, 4, 5 or 6 for authentication of forgery of a digital image.

A computer-readable recording medium having recorded thereon a program for performing an operation by the method of extracting a digital watermark according to claim 8 or 9 for integrity verification by forgery of a digital image.