A Scalable and Format-Compliant Encryption Scheme for H.264 ...

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1. IntroductionDigital video is pervasive today; it finds applications in such diversifiedareas as remote education, telemedicine, surveillance, IP TV and video-ondemand.In order to cater for heterogenous networks and various terminaldevices, many video coding schemes (e.g., [1, 2]) have been designed. However,few of them are widely deployed due to low compression efficiencyand/or non-scalability. Fortunately, after at least 20 years of research andexperiments, the scalable extension of H.264/AVC (Advance Video coding)[3, 4] was finally adopted as an international standard for video coding in2007. Generally speaking, SVC (Scalable Video Coding) achieves significantimprovement in coding efficiency and scalability, making it especially attractivein today’s ubiquitous networking environments.When a video stream is disseminated over an open network, an adversaryis able to eavesdrop the content. A naïve way to thwart the adversary isto treat the video stream as non-structural data, encrypt the bitstream asa whole, and distribute the ciphertext bitstream. However, this naïve approachis not suitable for secure SVC delivery over heterogeneous networksbecause the protected bitstream which loses the scalable feature can causehigh computational overhead for adaptation. In addition, several SVC encryptionschemes [5, 6, 7, 8] were proposed for MPEG-4 FGS (Fine grainscalability) and wavelet-based SVC.Encryption schemes for SVC should satisfy the following properties:• Security: No information of the original video content can be deduciblefrom ciphertext.• Scalability: The encrypted streams preserve end-to-end scalability fordelivery. That is to say, the header of NAL (Network Abstract Layer)should be compliant to SVC specification such that anyone can downgradethe video by simply discarding some of the protected bitstream.• Format-compliance: The encrypted streams are compliant to the SVCspecification and compatible to the standard SVC decoder. To this end,the encrypted bitstream shall have two properties. (1) The encrypteddata shall not include the SVC markers, i.e., emulation-free; (2) Theencrypted data do not have illegal codeword. Otherwise, a standardplayer may crash when it plays the encrypted bitstream directly. Asthe crashing of decoder may leak memory leakage and eventually lead2
to abnormal system behavior. Even worse, memory leakage leads toserious kernel stability issues, or other attacks such as denial of serviceattack.• Computational complexity: The encryption and decryption operationsshould incur limited computational resource and time.• Compression overhead: The encryption should have no or little effecton compression efficiency.In this paper, based on the RTP payload format for SVC video [9], theencryption scheme presented in this paper transforms a standard SVC bitstreaminto an encrypted SVC bitstream which has the same format as theoriginal one. To this end, we encrypt VCL (video coding layer) NALU (NetworkAbstract Layer Unit) of the base layer into either SEI (SupplementEnhancement Information) NALU or PACSI (Payload Content ScalabilityInformation) NALU. For each enhancement layer, we replace a VCL NALUwhose type is 20 with an encryption of PACSI NALU. Our analysis and experimentalresults indicate that the encrypted SVC bitstream is secure andformat-compliant, and at the same time, the computational complexity andcompression overhead are small.The remaining of this paper is organized as follows. Related works areexplained in Section 2, and the SVC bitstream structure is introduced inSection 3. Section 4 elaborates our encryption scheme. Section 5 addressesthe performance of the proposed scheme. Section 6 presents experimentalresults. Finally, conclusions are drawn in Section 7.2. Related WorkThere are several video encryption delivery methods [10] based on tradeoffbetween security and performance in terms of scalability, format-compliance,computation complexity, and compression overhead. The classification ofSVC encryption algorithm is based on the relation between encryption andcompression. We consider two classes of algorithms as follows.2.1. Compression-integrated encryptionCompression-integrated encryption scheme simultaneously performs encryptionand compression (encryption is part of compression), which preservesscalability and format-compliant properties, and causes little computationalcomplexity. For example, in the schemes [11, 12, 13, 14, 15, 16]3
Page 1: A Scalable and Format-Compliant Enc
Page 5 and 6: Table 1: NALU TYPESNALU type Descri
Page 7 and 8: Figure 2: The structure of base lay
Page 9 and 10: poral base layer is used as referen
Page 11 and 12: Table 2: Mapping between Forbidden
Page 13 and 14: PACSIunit NALPrefixunit NALNRI 14 R
Page 15 and 16: • A new PACSI NALU (30) including
Page 17 and 18: Figure 9: The flowchart of bitstrea
Page 19 and 20: • For any PACSI NALU (30) whose D
Page 21 and 22: an SVC-aware router is required to
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Page 25 and 26: Figure 13 and Figure 14 illustrate
Page 27 and 28: Table 5 states that the overhead in
Page 29 and 30: References[1] D. L. Goeckel, Adapti
Page 31: [22] H. Hellwagner, R. Kuschnig, T.

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