Security and protection of digital images by using watermarking methods

Andreja SamčovićFaculty of Transport and Traffic

EngineeringUniversity of Belgrade, Serbia

Gjovik, june 2014.

Digital watermarking in telemedicine: applications

and securityBilateral project with the

University of Ljubljana, Slovenia

I. Introduction

Digital watermarking - process of hiding a watermark in multimedia

Robust watermarking Should not be possible to be removed Copyright information Secret information Multimedia communication Telemedicine – health care when distance

separates

I. Introduction

Recent advances in telemedicine Need for multimedia communication Security - one of the most significant

problems in multimedia Confidently (unauthorized information

revealing), Integrity (unauthorized withholding of

information or resources), Availability (unauthorized withholding of

information or resources

I. Introduction

European Information Technology SecurityEvaluation Criteria

Careful analysis of security requirements Multimedia - related security problems Protect multimedia systems against incoming

attacks How much a multimedia file differs from its

original

II. Watermarking techniques

Mark is inserted into an original digital content

Data payload, key size, transparency, robustness, false positive rate, complexity, capacity, verification procedure, and invertibility

General key requirements Cryptography

II. Watermarking techniques

Transparency - human sensory factors Attacks are transforms designed by malicious

users Active attacks - the hacker tries to remove

the watermark Passive attacks - to determine whether a

mark is present or not Collusion attacks Forgery attacks

II. Watermarking techniques

Complexity is the effort and the time we need to embed and retrieve a watermark

Capacity - how many information bits we can embed

Verification procedure Invertibility is the possibility of producing the

original data Spread Spectrum and the Informed

Embedding methods

Figure 1. Watermarking method as a noisy channel

MODULA-TION

CHANNEL#1

CHANNEL#2

DETECTION

MESSAGE

KEYKEY

MARK

ORIGINALIMAGE

MARKEDIMAGE

ATTACKS

PROCESSING

PROCESSEDAND ATTACKEDIMAGE

KEY

MESSAGE

III. Security

Security requirements Confidentiality, data integrity, data origin

authenticity, entity authenticity, and nonrefudiation

Cipher systems - private-key and some public-key cryptosystems

In medical applications, we can change media data with compression and scaling without content manipulation

III. Security

Message authentication codes (MACs), digital structures, fragile digital watermarks, and robust digital watermarks

MAC is a one-way hash function that is parameterized by a secret key – private key cryptosystems

Authentication protocols Digital signatures - public key cryptosystems

IV. Applications

Integrate multiple media Multimedia communication technology Patient history, demographics, billing,

scheduling, laboratory reports Teleconsultation and telediagnosis Telediagnosis – primary diagnosis at the

location of patient Telediagnosis – at remote location

IV. Applications

The entire range of telemedicine applications, including the transfer of large medical images

Bursty nature of transferring medical images Teleconsultation and remote monitoring –

guaranteed QoS Transfer of the medical image Statistical multiplexing - video, audio, image

and patient data, transport cost can be reduced

IV. Applications

Interactive sharing of medical images and patient through a telemedicine system

Synchronous telediagnosis - high communication bandwidth

Asynchronous telediagnosis - lower communication bandwidth

Emergency medicine

IV. Applications

Examples of clinical applications Teleradiology X-ray, computer tomography (CT), magnetic

resonance imaging (MRI), ultrasound (US), positron emission tomography (PET), single-photon emission-computed tomography (SPECT)

Relevant patient information

V. Concluding remarks

Medical imaging modalities 3D image processing and visualization

techniques Telemedicine applications from the

multimedia communication perspective Telemedicine systems are able to offer many

health care services that could only be dreamed just a few years ago

Teleconsultation, teleradiology and teleelectroneuromiography

V. Concluding remarks

Watermarking – a viable solution Medical data security Medicals data structure and complexity Security mechanisms Enhanced multimedia communication

capability

Digital Image Watermarking by Spread Spectrum method

I Spread Spectrum Techniques

Watermark should not be placed in perceptually insignificant regions of an image

Problem – how to insert a watermark Frequency domain – communication channel Spread spectrum communications Narrowband signal is transmitted over much larger

bandwidth Similarly, watermark is spread over many frequency

coefficients Energy in one coefficient is undetectable

I Spread Spectrum Techniques

Direct Sequence Spread Spectrum (DS-SS) Frequency Hopping Spread Spectrum (FH-SS) DS-SS – low level wideband signal can be hidden within

the same spectrum as high power signal Core component – Pseudo Random Noise Sequence

(PRNS) Original bit stream is multiplied by PRNS At the receiver, low level wideband signal will be

accompained by the noise Suitable detector – signal can be squezzed back

I Spread Spectrum Techniques

FH-SS algorithm – periodic change of transmission frequency

Hopset – set of possible carrier frequencies Each channel – spectral region with central frequency in

the hopset Bandwidth includes most of the power in a narrow band

modulation burst Data is sent by hopping the transmitter carrier On each channel, small bursts of data are sent using

narrowband modulation

II Watermarking Embedding DS-SS is used in the watermarking generating FH-SS determines embedding positions Sequence of information bits is spread by multiplying with

large factor, called chip-rate Size of the sequence is equal to the value of chip-rate

multiplied by number of information bits Spread sequence is modulated with binary pseudo-noise

sequence Amplified with a locally adjustable amplitude factor

INFORMATION BITS {-1,1}

SPREADING WITH CR

PSEUDO RANDOMNOISE SEQUENCE

SECRETKEY

GENERATING RANDOM

POSITIONS

ORIGINALIMAGE

WATERMARKEDIMAGE

A

B

AMPLITUDE

Fig.2 Block diagram of the watermarking scheme, with blocks A) watermarking generating, B) determining of locations

II Watermarking Embedding Watermark process is illustrated in the block A Each bit of the watermark signal will be embedded into

some assigned locations Randomly determined by a key-based FH-SS within the

image frame Each watermark bit will be dispersed over its

corresponding locations Location determining process is shown in the block B 256 x 256 pixels – 65536 available pixels are considered as

hopset

II Watermarking Embedding If 10 % of image frame is required to embed the

watermark, 6544 locations will be pseudo-randomly determined

Selected locations are used to perform watermark embedding

Each watermark bit is embedded by additive operation Some of the selected pixels will carry the watermark signal Correlation is performed by demodulation

III Some Results 8-bit standard images (Airplane, Barbara, Boat) PSNR is used to evaluate the quality of the watermarked

images Embedding the watermarking signal into parts of the

Barbara at different levels Image area is decreased, reduced the amount of

information rate Reducing the block size is used to carry the watermark

signal Some selected bits are used to carry the watermark signal

30

35

40

45

50

10 20 30 40 50 60 70 80 90 100

Embedding area (%)

PSN

R (d

B)

Fig.3. PSNR value at various level of embedding area within

the image Barbara

30

32

34

36

38

40

42

44

46

48

10 20 30 40 50 60 70 80 90 100

Embedding area (%)

PSN

R (d

B)

Fig.4. PSNR values at different block sizes (the highest curve corresponds to 3,

in the middle to 4, while the lowest corresponds to 5 block size)

Table 1. The smallest value of chip-rate required at various block sizes

ORIGINALIMAGE

BLOCKSIZE 3

BLOCKSIZE 4

BLOCK SIZE 5

AIRPLANE 20 65 235

BOAT 20 95 270

BARBARA 18 68 245

III Some Results Since a smaller chip-rate is used, amount of information

bits would be increased Table shows the smallest value of chip-rate required to

correctly recover the embedded bits Fig.4 – block size used to carry the watermark signal was

changed The quality of watermark signal is improved when

watermark is embedded into some parts Security level is the same as in the whole image frame

III Some Results Advantage of FH-SS: embedded signal is robust to some

potentional attacks Watermark could be extracted without using the original in

spread spectrum The input image is highpass filtered to remove major

components Filtered image is then demodulated with the pseudo-noise

signal

IV Conclusion Watermarking based on spread spectrum FH-SS to locate watermark embedding DS-SS to generate the watermark signal Improved the quality of watermarked image The same level of security Decreasing of the embedding area could be compensated

by adding the watermark signal into some selected bits within a pixel