Security and protection of digital images by using watermarking methods

Transcription

1 Security and protection of digital images by using watermarking methods Andreja Samčović Faculty of Transport and Traffic Engineering University of Belgrade, Serbia Gjovik, june 2014.

2 Digital watermarking in telemedicine: applications and security Bilateral project with the University of Ljubljana, Slovenia

3 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

4 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

5 I. Introduction European Information Technology Security Evaluation 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

6 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

7 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

8 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

9 MESSAGE PROCESSING MODULA- TION CHANNEL #1 CHANNEL #2 DETECTION KEY MARK MARKED IMAGE PROCESSED AND ATTACKED IMAGE MESSAGE ORIGINAL IMAGE ATTACKS KEY Figure 1. Watermarking method as a noisy channel

10 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

11 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

12 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

13 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

14 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

15 IV. Applications Examples of clinical applications Teleradiology X-ray, computer tomography (CT), magnetic resonance imaging (MRI), ultrasound (US), positron emission tomography (PET), singlephoton emission-computed tomography (SPECT) Relevant patient information

16 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

17 V. Concluding remarks Watermarking a viable solution Medical data security Medicals data structure and complexity Security mechanisms Enhanced multimedia communication capability

18 Digital Image Watermarking by Spread Spectrum method

19 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

20 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

21 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

22 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

23 INFORMATION BITS {-1,1} A SECRET KEY B SPREADING WITH C R GENERATING RANDOM POSITIONS AMPLITUDE WATERMARKED IMAGE PSEUDO RANDOM NOISE SEQUENCE ORIGINAL IMAGE Fig.2 Block diagram of the watermarking scheme, with blocks A) watermarking generating, B) determining of locations

24 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 available pixels are considered as hopset

25 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

26 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

27 50 PSNR (db) Fig.3. PSNR value at various level of embedding area within the image Barbara Embedding area (%) PSNR (db) 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) Embedding area (%)

28 Table 1. The smallest value of chip-rate required at various block sizes ORIGINAL IMAGE BLOCK SIZE 3 BLOCK SIZE 4 BLOCK SIZE 5 AIRPLANE BOAT BARBARA

29 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

30 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

31 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