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1、Applications of Data Hiding in Digital Images,自動化資訊處理實驗室 報告人:李惠龍,2,Outline,Introduction Difference between cryptography and steganography Applications Covert communication Digital watermarking Watermarking for tamper detection and authentication Our application,3,Steganography,The art of concealed c
2、ommunication Hiding of secret messages within another message (or carrier) Make info. imperceptible Keep existence of info. secret,4,Difference between cryptography and steganography,Cryptography: Protect the content of messages Scramble data such that it is unreadable Ciphertext attracts attackers
3、for decryption Steganography: Conceal the existence of messages Hide data in another data Hide the existence of communication Stegotext minimizes attackers interest,5,Difference between cryptography and steganography,A secure crypto-system One in which an adversary who understands the system, but do
4、es not know the key, can not recover the data A secure stego-system One where an adversary who understands the system, but does not know the key, can obtain no evidence that a communication has taken place,6,Robustness The ability to extract hidden information after common image processing operation
5、s: linear and nonlinear filters, lossy compression, contrast adjustment, recoloring, resampling, scaling, rotation, noise adding, cropping, printing / copying / scanning, D/A and A/D conversion, pixel permutation in small neighborhood, color quantization (as in palette images), skipping rows / colum
6、ns, adding rows / columns, frame swapping, frame averaging (temporal averaging), etc.,Undetectability Impossibility to prove the presence of a hidden message. This concept is inherently tied to the statistical model of the carrier image. The ability to detect the presence does not automatically impl
7、y the ability to read the hidden message. Undetectability should not be mistaken for invisibility a concept related to human perception.,Invisibility Perceptual transparency. This concept is based on the properties of the human visual system or the human audio system.,Security The embedded informati
8、on cannot be removed beyond reliable detection by targeted attacks based on a full knowledge of the embedding algorithm and the detector (except a secret key), and the knowledge of at least one carrier with hidden message.,Properties of hiding schemes,7,Applications,Covert communication (steganograp
9、hy) Digital watermarking (robust message embedding)Copyright protection of digital images (authentication)Fingerprinting (traitor-tracing)Adding captions to images, additional information to videos Watermarking for tamper detection and authentication,8,Covert Communication,Purpose: To conceal the ve
10、ry presence of communication,to make the communication invisible.,Encryption: To make the message unintelligible,Secret communication?! I just posted a picture of my cat on my web page!,Warden Willie,Andy,Bob,9,Covert Communication,Secret message,Encryption Unit,Carrier Image,Embedding Algorithm,Mod
11、ified Carrier,- Encryption and steganographyprovide double protection - Randomized message is easierto hide,10,Copyright protection of digital images (authentication),Original,+,=,Watermark,Watermarked image,Robustness against all kinds of image distortionRobustness to intentional removal even when
12、all details about the watermarking scheme are known (Kerckhoffs principle)Watermark pattern must be perceptually transparentWatermark depends on a secret keyRobustness to over-watermarking, collusion, and other attacks,11,Robust, secure, invisible watermark, resistant with respect to the collusion a
13、ttack (averaging copies of documents with different marks).,Fingerprinting or traitor tracing,Marking copies of one document with a customer signature.,W1,W2,WN,N customers,+,original,12,Typical application:Adding subtitles in multiple languagesAdditional audio tracks to videoTracking the use of the
14、 data (history file)Adding comments, captions to imagesWatermark requirements:Moderately robust schemeRobustness with respect to lossy compression, noise adding,and A/D D/A conversion Original images (frames) not available for message extractionSecurity requirement not so strong Fast detection, wate
15、rmark embedding can be more time consuming,Adding captions to images, additional information to videos,13,Watermarking for tamper detection and authentication,Watermarked image,altered image,Verification result,14,Our application,Sensitive information that is not encrypted (or that is encrypted with
16、 poor cryptographic techniques) and that is transmitted between two wireless devices may be intercepted and disclosed. Provide a secret communication channel Under application layer Provide double protection (encryption and steganography),15,Our application,Wireless network,16,References,www.lib.nctu.edu.tw/new/data/數位典藏版權保護技術.pdf www.ws.binghamton.edu/fridrich/Research/tutor1.ppt,
