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CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION TO INFORMATION SECURITY

Due to the advancement of technology, each and every individual

and organizations can reach any individual or organizations worldwide, at any

given point or time in the world through internet without any geographic

boundaries or time of day. In healthcare there is a need for fast and quick

diagnosis of patient condition and discussion between physicians through

internet to make best decision about patient care. The recent advances in

information and communication technologies, which provide new means to

access, handle and move medical information, leads to compromise their

security due to their ease of manipulation and replication.

Medical information record of a patient comprises of clinical

examinations, diagnosis annotations, prescriptions, histological and other

findings and images. In the digital format they are centered in the Electronic

Patient Record (EPR) through which information is gathered over years by a

number of health professionals and used for various purposes. All patients

records, electronic or not, linked to the medical secrecy, must be confidential.

The digital handling of EPR on network requires a systematic content

validation which is aimed at quality control: actuality (precise interest of the

information at a given instant) and reliability (authentication of the origin and

integrity). Security of medical information, derived from strict ethics and

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legislatives rules, gives rights to the patient and duties to the health

professionals which impose three mandatory characteristics (Ping et al. 2007):

Confidentiality means that only the entitled users, in the

normally scheduled conditions, have access to the

information.

Reliability which has two aspects; i) Integrity: the information

has not been modified by non-authorized people and ii)

Authentication: a proof that the information belongs indeed to

the correct patient and is issued from the correct source.

Availability is the ability of an information system to be used

by the entitled users in the normal scheduled conditions of

access and exercise.

1.2 DIGITAL WATERMARKING

Watermarking is the process in which meaningful information or

message is inserted into an image such a way that it is imperceptible to human

observer but easily detected by computer algorithm.

In general, the watermarking system discussed here consists of an

embedder and a detector, as shown in Figure1.1. The embedder takes two

inputs. One is the message that is to be encoded as a watermark and the other

is the cover image in which the watermark is to be embedded. The output of

the watermark embedder is typically transmitted or recorded.

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Figure 1.1 A generic watermarking system

Cox et al. (2008) have proposed Watermarking is closely related to

the fields of information hiding and steganography. These three fields have a

great deal of overlap sharing many technical approaches.

Information hiding (or data hiding), refers to either making the

information imperceptible (as in watermarking) or keeping the existence of

the information as secret.

Cox et al. (2008) have proposed steganography is a term derived

from the Greek words steganos, which means “covered” and graphia, which

means “writing” It is the art of concealed communication and the very

existence of a message as secret.

The sudden increase in watermarking interest is most likely due to

the increase in concern over copyright protection of content. The internet is an

excellent distribution system for digital media because it is inexpensive,

eliminates warehousing and stock and delivery is almost instantaneous.

However, content owners also see a high risk of piracy.

Li & Memon (2007) have proposed digital watermarking consists

of three major components: watermark generator, embedder and detector as

shown in Figure 1.2.

Cover Image

WatermarkEmbedder

Watermark

WatermarkDetector

Detected WatermarkMessage

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(a) Watermark generation

(b) Watermark embedding

(c) Watermark detection

Figure 1.2 Fundamental components of digital watermarking

A watermark generator generates desired watermark(s) for a

particular application, which are optionally dependent on some keys.

Watermarks are embedded into the object by a watermark embedder,

sometimes based on an embedding key. Whereas, a watermark detector is

WatermarkDetection

WatermarkedImage-data

Watermark

OriginalImage-data

EstimatedImage-data

WatermarkEmbedding

Watermark

OriginalImage-data

WatermarkedImage

EstimatedMessage

WatermarkGeneration

Message and/other image-data

OriginalImage-data

Watermark

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responsible for detecting the existence of some predefined watermark in the

object. It is sometimes desirable to extract a message as well.

Cox et al. (2008) have proposed the first technology content that

attracts owners is cryptography. Cryptography is probably the most common

method of protecting digital content. It is certainly one of the best developed

as a science. The content is encrypted prior to delivery and a decryption key is

provided only to those who have purchased legitimate copies of the content.

The encrypted file can then be made available through internet but would be

useless to a pirate without an appropriate key. Unfortunately, encryption

cannot help the seller monitor, how a legitimate customer handles the content

after decryption. A pirate can actually purchase the product, use the

decryption key to obtain an unprotected copy of the content and then proceed

to distribute illegal copies. In other words, cryptography can protect content

in transit, but once decrypted, the content has no further protection. Thus,

there is a strong need for an alternative or complement to cryptography; a

technology that can protect content even after it is decrypted. Watermarking

has the potential to fulfill this need because it places information within the

content where it is never removed during normal usage. Watermarking has

been considered useful for copy prevention and copyright protection

applications.

1.2.1 Classification of Digital Watermarking

Watermarks can be classified according to their various

characteristics (Sadicoff 2004).

Perceptibility

A watermark can be automatically inserted in an image as noise and

utilize the perception masking capabilities of the human eye to make this

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watermark just barely visible. It does not interfere with the image and can

only be perceived if the user concentrates on the watermark. This watermark

can be inserted in the image as a whole or on a non-intrusive corner, by some

modification. The most interesting advantage of this method is that it can be

automatically inserted. It blends with the image by raising or reducing the

brightness of a few pixels hence it is not easily removed by automatic

methods.

Fidelity

Most of the watermark applications intend to insert external

information on images without disturbing the original image perception.

Fidelity of a watermark is the characteristic that defines how close the

watermarked file is from the original data. It can be determined by

statistically averaging, throughout many images, the percentage of data that

remains the same when a watermark is inserted using the same method and

parameters.

Robustness

Image might be subject to many forms of distortions or alterations

before they reach the final user, especially if an attacker decides to try to

remove a watermark by performing a variety of transformations. In a typical

operation, an image might suffer contrast or brightness variations to enhance a

specific area, which itself is not illegal most of the times but might erase a

watermark whose insertion and deletion depends on color or brightness

coefficients.

The most robust solution for a watermark is to encode it in a

perceptually significant area. If this is perpetrated, any significant change in

the watermark that would affect either its detection or integrity which can

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affect the integrity of the image, effectively reducing the image quality and in

most cases its usability. The watermark’s robustness becomes then directly

related to the document’s perception quality.

1.2.2 Watermarking Techniques

Miller et al. (1999) have proposed the watermarking techniques are

divided into two basic categories.

Spatial domain watermarking, in which the Least Significant

Bit (LSB) of the image pixels is replaced with that of the

watermark (authentication text). This method of spatial

domain watermarking is very susceptible to noise. A more

robust watermark can be embedded in the same way that a

watermark is added to paper. In this method, a watermark

symbol may be superimposed over an area of the picture and

then some fixed intensity value for the watermark is added to

the varied pixel values of the image. The resulting watermark

may be visible or invisible depending on the value of the

watermark intensity. The main disadvantage of spatial domain

watermarks is that the picture cropping can be used to

eliminate the watermark.

Frequency domain watermarking, in which the image is first

transformed to the frequency domain and then the low

frequency components are modified to obtain the

authentication text. Watermarking can be applied in the

frequency domain by applying transforms like Fast Fourier

Transform (FFT), Discrete Fourier Transform (DFT), Discrete

Wavelet Transform (DWT) and Discrete Cosine Transform

(DCT). Similar to spatial domain watermarking, in this

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method the values of the chosen frequencies are altered from

the original to contain the watermark (authentication text).

Since high frequencies will be lost by compression or scaling,

the watermark signal is applied to the lower frequencies or

applied adaptively to frequencies that contain important

information of the original picture. Also, watermarks applied

to the frequency domain will be dispersed over the entirety of

the spatial image upon inverse transformation, hence this

method is not susceptible to defeat by cropping as the spatial

technique.

Watermarking in spatial and transform domains have different

advantages and disadvantages, which are shown in Table 1.1

Table 1.1 Advantages and disadvantages of watermarking in spatial

and transform domains

Types of processing Advantages Disadvantages

Spatial domain Comparatively simpleand faster operation

Vulnerable to compression,

geometric distortion, and

filtering

Transform domain Compression compatible,and robust against manygeometric distortions(e.g., rotation, scaling,translation, cropping) andfiltering

Comparatively higher

computational time and

complexity

The authentication of digital watermark-based approaches can be

classified as either fragile watermarking or semi-fragile watermarking. A

fragile watermarking can detect any possible modification of the pixel values.

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On the other hand, semi-fragile watermarking can distinguish content-

preserving operations from malicious manipulations, e.g., addition or removal

of a significant element of the image.

1.2.3 Digital Watermarking versus other Security Measures/Tools

Nyeem et al. (2012) have proposed digital watermarking has some

unique advantages, although few existing security measures/tools may serve

its other objectives together. For example, encryptions, cryptographic hash

functions (e.g., Message Authentication Code (MAC), Digital Signature (DS)

etc.), perceptual hashing, etc. An extensive comparison among them based on

various key properties and requirements of medical image applications is

made and presented in Table 1.2.

1.2.4 Applications of Digital Watermarking

Digital watermarks have been broadly and successfully deployed in

billions of media objects across a wide range of applications (cox et al. 2008).

Document and image security

Content protection for audio and video content

Communication of ownership and copyrights

Broadcast monitoring

Locating content online

Content identification and management

Authentication of contents and objects

Rich media enhancement for mobile phones

Source tracking

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1.3 SECURITY AND PRIVACY REQUIREMENTS IN

MEDICAL IMAGE

Medical image security is important when digital images and their

pertinent patient information are transmitted across public networks. One can

tamper the content of image evidence unscrupulously with Adobe Photoshop

as shown in Figure 1.3. For instance, it is possible to change an original

image with cancer to a new modified image. The original image is shown in

Figure 1.3 (a) and modified image is shown in Figure 1.3 (b).

Figure 1.3 (a) Original image (b) Modified image using Adobe

Photoshop 7.0

At present, Virtual Private Network (VPN) is used to protect the

integrity of patient records as a security measure. Mandates for ensuring

health data security have been issued by the federal government such as

Health Insurance Portability and Accountability Act (HIPAA), where

healthcare institutions are obliged to take appropriate measures to ensure that

patient information are provided it to the people who have a professional

need. Digital Imaging Communication in Medicine (DICOM) standards that

deal with security issues continues to be published by organizing bodies in

healthcare.

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1.3.1 Medical Information Security Requirements

Medical information security requirements are generally defined by

the strict ethics and legislative rules of the security policy/profile and

concerned entities must adhere to them. There are many widely used

guidelines and standards for protecting personal health information.

Development and implementation of the security and privacy protection

services derived from the standards depends upon the model and its

concerned entities. Nyeem et al. (2012) have proposed the most common

model used in medical image transfer consists of three individual domains,

namely: i) host organization/hospital’s Picture Archiving and Communication

System (PACS) (domain A), ii) communication network (domain B) and ii)

consultant (domain C) as depicted in Figure 1.4. Therefore in medical images,

security concerns arise only from the domain A (e.g., from acquisition of

medical images to storing them in PACS of the same hospital). In an off-line

model the security domains are isolated and communication is made via

interfaces; whereas, in on-line communication with a remote consultant

allowing access to the local PACS services of the legacy system.

Figure 1.4 Model for medical image transmission

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1.4 ADVANTAGES OF DIGITAL WATERMARKING FOR

MEDICAL IMAGE APPLICATIONS

Watermarking has received much attention recently for medical

image applications because of its various attractive attributes, which are listed

below (Ping et al. 2007):

Security and privacy: The fundamental and most attractive property of

watermarking is data hiding capability. The utmost confidentiality can be

maintained by hiding the private data into the images. Keeping necessary

medical information (e.g., EPR including demographic data, diagnostic

results, treatment procedures, region of interest etc.) hidden in medical

images may provide a better security against malicious tampering. Even that

is tampered intentionally or in an unintended manner, can be detected and

possibly recovered by using an appropriate watermarking scheme. Data

hiding, integrity control and authenticity can provide the required security of

medical images. For example, data-hiding objective of watermarking allows

inserting meta-data and other information so that the image is more useful or

easier to use. Integrity control objective of watermarking ascertains that the

image has not been modified in an unauthorized manner. Digital

watermarking allows permanent association of image content with proofs of

its reliability by modifying some image pixel values, independently of the

image file format. It can also operate in a stand-alone environment and has a

versatile message set. In addition, authenticity traces the origin of an image.

Avoiding detachment: The data hiding property of watermarking mentioned

above further facilitates annotation of necessary information to avoid

detachment. Millions of medical images are being produced in radiology

departments around the world, which have immense value to practicing

medical professionals, medical researchers, and students. Researches in this

field are being accomplished to embed patient data to medical images. If the

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EPR and the images are separate, the chance of detachment of patient data

from the image becomes higher. Misplacing a data will be very crucial in the

case of medical image. In order to avoid this misplacing or detachment,

watermarking offers necessary data embedding within the image itself.

Indexing: Another benefit stems from data hiding capability of watermarking

is indexing, where relevant keywords or indices can be embedded into the

images and used for effective archiving and retrieval of the images from

databases .

Non repudiation: In tele-radiology, distribution of the watermarked images

between Hospital Information System (HIS) may cause non repudiation

problem, where both the involved parties (e.g., hospital personnel and

clinician) may repudiate that they did not send the data. Along with other

advantages, watermarking is also promising to support non repudiation in

various multimedia applications. Hence, use of a key based watermarking

system may facilitate non repudiation in tele-radiology such that both parties

could be in safer side; where key used by the hospital could be their logos or

digital signatures.

Controlling access: Provision for using keys in watermarking schemes

further provides an alternative to access control mechanism, where

confidential meta-data can be accessed with the proper authoritative rights

given in terms of keys.

Memory and bandwidth saving: Storage space and bandwidth requirements

are important decisive factor for small hospitals financial economy. The

memory for storage can be saved to a certain extent in HIS by embedding the

EPR in the image. On the other hand, huge amount of bandwidth is required

for the transmission of the image data. The additional requirement of

bandwidth for the transmission of the metadata can be avoided if the data is

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hidden in the image itself. Since the EPR and the image can be integrated into

one, bandwidth for the transmission can be reduced.

1.5 OBJECTIVES AND APPLICATIONS OF

WATERMARKING FOR MEDICAL IMAGES

Popularity of internet has become a boon to patients and low capital

hospitals to utilize the facility to communicate with the clinicians for clinical

diagnosis purposes, where the security of medical images can presumably be

addressed to a considerable extent by inserting a properly selected additional

data into medical images through digital watermarking. A digital medical

image application is therefore one of the prospective target areas of using

digital watermarking. Studies show (Nyeem et al. 2012) that various

watermarking schemes can be used in medical images for i) origin

authentication ii) EPR annotation and iii) tamper detection and recovery of

medical images. Some important aspects of medical image watermarking

schemes for their different objectives are summarized below.

Origin authentication: Watermarking has received much interest in the

research for origin authentication of the medical images. The important

details can be stored in images imperceptibly, causing no harm to the ROI of

the images. This kind of brief descriptions can be hidden in images

immediately after the production of the images in the radiology departments.

This can be done by incorporating the watermarking in the different modality

machines namely, CT or MRI scanners. The database systems use the

mechanisms of granting and revoking privileges and of authorization control

to ensure the security of data with the permanent association of the

watermark. Observation suggests the following requirements for this type of

watermarking in tele-radiology (Nyeem et al. 2012):

i) The watermark should be invisible, blind and robust.

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ii) Watermark should incorporate the minimum information

required for the origin authentication.

iii) Embedding process must consider the ROI and proper

validation of a watermarking scheme such that the permanent

association of the watermark is reliable and safe for diagnosis.

Tamper detection and recovery (integrity control): Medical images in

different radiological modalities such as x-rays, ultrasounds and Magnetic

Resonance Imaging (MRI) contain vital medical information and can be

tampered with existing image processing tools that are easily available. Thus,

their protection and authentication seems of great importance and this need

will rise along with the future standardization of exchange of data between

hospitals, or between patients and doctors. Integrity of a medical image can

be achieved in three levels

i) Tamper detection

ii) Tamper localization

iii) Possible recovery by approximating the tampered region.

In order to achieve this along with the requirements of medical

image needs a watermark to be

i) Fragile and blind

ii) Reversible or RONI embedding based.

Hence, fragile watermarking help locate the tampered region with

its fundamental property that a watermark becomes invalid for any malicious

or un-intentional modifications in the watermarked image.

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If the origin authentication of a medical image is achieved by the

robust watermarking, fragile reversible watermarking (in the form of multiple

watermarking) can further locate and possibly recover any tampered region of

the watermarked image. This will allow the system to control the integrity as

well as authentication.

1.6 OBJECTIVES OF THE THESIS

The objectives of this research work are:

i) To develop a watermarking technique with hidden ROI that

maintains data integrity with secure transmission of images

from examination site to expert center.

ii) To improve the developed watermarking technique with

modified sub band in cat map and logistic map.

iii) To test the robustness and image quality of the developed

watermarking technique against various types of attacks.

1.7 ORGANISATION OF THE THESIS

The work reported in the thesis is organized into five chapters:

Chapter 1 gives an overview of watermarking, as well as on its

requirements, classification, applications and a categorization of attacks on

watermarking techniques.

Chapter 2 discusses literature review on Digital Imaging

Communication in Medicine image, watermarking and their application in

medical images, cryptography, reference watermarking scheme and image

tiling.

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In Chapter 3 describes a new watermarking scheme hiding the DS

which include patient data embedded randomly into the LSB border of the

image. The DWT of ROI - Most Significant Bit (MSB) embedded into the

LSB middle of the image. The Result shows the ability to hide and retrieve

DS in RONI, while ROI, the most important area for diagnosis, is retrieved

exactly at the receiver side.

A novel method is proposed for hiding ROI and patient details into

tiled RONI of encrypted medical image using stream cipher. Experimental

results demonstrate that the proposed scheme can embed a large amount of

data while keeping high visual quality of test images.

A new method by decomposing cover image using WPT and then a

reference image is created by shuffling the positions of pixels using cat map.

For embedding, modify the singular values of reference image with singular

values of ROI bit plane. Finally, a reliable ROI is extracted from the

transmitted image. The feasibility of this method depends on number of

iteration in cat map and number of wavelet packet decomposition.

Another framework to hide ROI is proposed using WPT. The

original cover image is transformed into wavelet packet domain and the

robust sub band of wavelet packet domain singular values is modified with

singular values of ROI. The modified sub band is applied with cat map and

logistic map to increase the security of the algorithm. The watermark image is

obtained by reconstructing the wavelet packet transform with modified sub

band. Experimental result shows the robustness of this algorithm with various

types of attacks.

A novel robust and secure method for hiding ROI is proposed in

frequency domain using singular value decomposition and chaotic maps. The

region of interest is then transformed into frequency domain and a reference

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image is formed by using cat map. The original image is divided into tiles.

The centre tile is chosen for watermark embedding. Embedding in the centre

tile enhances robustness than the other tiles. Watermark is then embedded

into the original image by modifying singular value of reference image using

the singular value of the centre tile of the original image. The security of the

scheme depends on transmission of reference image. The security of

reference image is enhanced using logistic map. The feasibility of this method

and its robustness against different kind of attacks are verified by computer

simulations and experiments.

Chapter 4 focuses on the results and discussion, finally conclusion

from analysis are presented with future perspective in Chapter 5.