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Multimedia Encryption

Multimedia Encryption. Sistem Multimedia. Multimedia Encryption. Special application of general encryption to multimedia such that the content cannot be rendered intelligibly or to an acceptable perceptual quality.

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Multimedia Encryption

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  1. Multimedia Encryption Sistem Multimedia

  2. Multimedia Encryption • Special application of general encryption to multimedia such that the content cannot be rendered intelligibly or to an acceptable perceptual quality. • Have a number of unique requirements and desirable features that a general cryptosystem lacks. • Different applications may have a different list of requirements and a different order of priorities. • Trade-off may be necessary

  3. Applications • Confidential videoconferences • Confidential facsimile transmissions • Medical image transmission and storage • Streaming media • DVD content protection • Pay-TV • Digital transmission through IEEE 1394 interface

  4. Characteristics of Multimedia Applications • Characteristics • High data rate • Power hungry • Real-time constraint • Continuous • Synchronous • Loss-tolerant • Prioritized components • Different values of content • Different security requirements • Different distribution channels • DVD, Satellite TV, Internet, wireless

  5. Box Office Revenues vsTime

  6. Major Requirements and Desirable Features • Complexity is an important consideration • Real-time applications, low-power device • Content leakage (or perceptibility) • Content degradation vs. secrecy • Compression efficiency overhead • Due to change of compression parameters/procedure, change of data statistics, additional header etc. • Error resilience. • Error confinement in lossynetwork, synchronization • Adaptability and scalability • Dynamic bandwidth/resources, Encryption be transparent to an adaptation process

  7. Major Requirements and Desirable Features(cont.) • Multi-level Encryption • Enable multiple accesses: resolution, quality, size, frame rate • “what you see is what you pay “ • Syntax compliance • Transparent , “backward”compatibility, inherit other nice properties of compression standards. • Content agnostic • Encryption does not depend on content types or the specific coding technology • E.g., Windows Media Rights Manager , OMA’sDRM • Random access, transparency, scene change detection without decryption

  8. Encryption and Compression

  9. Security Break of Multimedia Encryption • Complete break • Recover full plain bitstreamby finding the key etc, • Perceptual break • Render acceptable perceptual quality or recover certain content information without a key • Local break • Deduce a local plain bitstream/content information • Information deduction • Gain certain information, less severe break

  10. Attacks on Multimedia Encryption • Traditional attacks • Additional attacks that exploit the unique features of multimedia data • Statistical attack • Exploit correlation between different portions of multimedia data • Especially for selective encryption • Compression makes the attack difficult, fortunately • Error-concealment based attack • Perceptual redundancy exists in compressed media • Perceptual break is possible, i.e. conceal encrypted data

  11. Multimedia Encryption Approaches • Conventional/Naïve approach • Encrypt a compressed codestreamas a whole • Full Encryption • Selective Encryption • Joint Compression and Encryption • Syntax-Compliant Encryption • Scalable Encryption and Multi-Access Encryption

  12. Conventional Approaches • Directly distort visual data in spatial domain • Difficult to compress, potentially high complexity • Vulnerable to correlation attacks • Encrypt compressed data using DES etc. • Significant processing overhead • Difficulty in some real-time application with low-power device • Plain text attack using known syntax • Not secure for adaptation at intermediate nodes • require key to decompress/decrypt/re-code/re-encrypt • Little transparency

  13. Fast Encryption • Encrypt half of the compressed bitstream( Qiao& Nahrstedt’97 ) • Using XOR + DES • Encrypt (A, B) as (DES(A), (A XOR B) ) • Secure, speedup by a factor of two

  14. Full Encryption • Approach • Partition and packetizecompressed bitstreaminto structured data packets with header and data field • Apply encryption to the data field and leave headers unencrypted • Decryption info inserted into headers • Usually works with a multimedia format that supports encryption,e.g., Microsoft’s ASF • Strength • Allow parsing and extracting basic info without decryption • Highest security, small overhead for decryption info • Content agnostic • Limitation: complexity, limited flexibility

  15. Selective Encryption • Only I-frame/blocks encrypted (Maples & Spanos’95, Meyer & Gadegast’95 ) • Reduce processing overhead/delay • Not sufficient security • Plain text attack using known syntax • Not very secure for trans-coding • Little transparency • Sign bits, MVs(Shi & Bhargava’98, Zeng & Lei’99, Wen et al’01) • Privacy/security low due to information leakage • Useful for apps focusing on introducing quality degradation

  16. Joint Scrambling and Compression • Shuffle DCT coefficients within 8x8 block (Tang 96) • Randomize 8x8 DCT coefficient scan order • Simple • Some level of security • Local scrambling -> spatial energy distribution unchanged -> less effective scrambling • Significantly reduce compression efficiency (up to 50%) –destroy run-length statistics • Shuffle lines of wavelet coefficients ( Macq& Quisquater’94 ) • Change 2-D statistical property, • Reduce compression efficiency

  17. Joint Scrambling and Compression • Selective scrambling in transform domain, prior to compression (Zeng & Lei’99) • Advantages • Simple and efficient. • Provides different levels of security, • Allows more flexible selective encryption • easier for locating what data to be selected • Limited adverse impact on compression efficiency, • Allow transparency • Allow trans-coding without decryption • Allow other useful features without decryption

  18. Overview

  19. Wavelet Based Systems • A 3-level subbanddecomposition • Allow some level of transparency • e.g, free access to low resolution • require key for high definition TV

  20. Wavelet Based Systems • Goal: • Scrambling/shuffling that does not destroy statistical properties of each subband • Selective bit scrambling • Sign encryption • sign bits: “uncompressible”, but critical to image quality • Block shuffling • Divide each subandinto kblocks • Shuffle the blocks within a subband • retain local2-D statistics • Different shuffling tables for different subbands

  21. Wavelet Based Systems • Block rotation • Rotate each block • Special case of shuffling coefficients within block

  22. Security Analysis • Sign encryption • M: # of non zero coefficients • 2Mtrials (including inverse transform) for complete recovery • example: M=256 ------> 1075trials • Block shuffling • kblocks, nzero blocks • # of different permutation: k!/n! • example: k=64, n=48 ----> K!/n!=1028 • each permutation requires an inverse wavelet transform • Block rotation (+shuffling) • # of configuration: (8*k)!/(8*n)! >>K!/n! • Other attacks? Your exercises!

  23. Wavelet-based System

  24. Wavelet-based SystemPSNR Table 1: Impact of different scrambling techniques on compression efficiency. Image sizes are 512x512, 5-level decomposition, 64 blocks each band.

  25. DCT Based Systems • JPEG/MPEG/H.26x • Video compression • GOP (I BBPBBP…) • I: intra-frame • P, Bpredictive-coded frames • block: 8x8, for DCT coding, • zigzagordering of DCT coefficients • Macroblock(MB): 4 lum. blocks + 2 chrom Blocks • unit for motion compensation • intra-coded vs. predictive coded • Slice: a horizontal strip of MBs

  26. DCT Based Systems • DCT coefficient scrambling • Sign encryption • Coefficient shuffling within each slice • shuffle coefficients of sameband • little impact on compression efficiency • each band has a different shuffling tables • Motion vector scrambling for P, B frames • Sign flipping • MV shuffling within each slice • Important for distorting motion information • Dynamic-keys for more secure video transmission

  27. I-Frames of DCT-based System

  28. I-Frames of DCT-based System Table 2: Impact of different scrambling techniques on compression efficiency for one I frame of “carphone”sequence.

  29. DCT-based System (Sequence) Table 3: Impact of different scrambling techniques on compression efficiency for 41 (one I frame followed by 40 P frames) frames of “carphone”sequence

  30. Video Demo

  31. References • T. Maples and G. Spanos, “Performance study of a selective encryption scheme for the security of networked, real-time video," Proc. 4th Inter. Conf. Computer Communications and Networks, Las Vegas, Nevada, Sept. 1995. • J. Meyer and F. Gadegast, “Security mechanisms for multimedia data with the example MPEG-1 video,”http://www.cs.tuberlin.de/phade/phade/secmpeg.html, 1995. • C. Shi and B. Bhargava, “A fast MPEG video encryption algorithm,”Proc. ACM Multimedia, pp. 81-88, 1998. • L. Tang, “Methods for encrypting and decrypting MPEG video data efficiently,”Proc. ACM Multimedia, 1996. • W. Zeng and S. Lei, “Efficient frequency domain selective scrambling of digital video”, IEEE Tran. Multimedia,vol. 5, no. 1, pp. 118-129, March 2003. A preliminary version also in Proc. ACM Multimedia, Nov. 1999. • Bin Zhu, “Multimedia encryption, “book chapter in Zeng, Yu, and Lin (Eds), Multimedia Security Technologies for Digital Rights Management, ISBN: 0-12-369476-0, Elsevier, July 2006.

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