This paper presents a compliant encryption method for JPEG 2000 codestreams such that the encryption process does not introduce superfluous JPEG2000 markers in the protected codestream, i.e., the protected codestream preserves the syn-tax of the original codestream. The proposed encryption method works with any standard ciphers, incurs no stor-age overhead, introduces negligible computational cost and maintains all the desirable properties of the original JPEG 2000 codestream such as error resilience and scalability. 1

DENG, Robert H.

WU, Yongdong

Yongdong Wu

Robert H. Deng

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R.H.: Compliant encryption of JPEG2000 codestreams

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Singapore Management UniversityInstitutional Knowledge at Singapore Management UniversityResearch Collection School Of Information Systems School of Information Systems10-2004Compliant Encryption of JPEG2000 CodestreamsYongdong WUInstitute for Infocomm ResearchRobert H. DENGSingapore Management University, robertdeng@smu.edu.sgDOI: https://doi.org/10.1109/ICIP.2004.1421854Follow this and additional works at: https://ink.library.smu.edu.sg/sis_researchPart of the Information Security CommonsThis Conference Proceeding Article is brought to you for free and open access by the School of Information Systems at Institutional Knowledge atSingapore Management University. It has been accepted for inclusion in Research Collection School Of Information Systems by an authorizedadministrator of Institutional Knowledge at Singapore Management University. For more information, please email libIR@smu.edu.sg.CitationWU, Yongdong and DENG, Robert H.. Compliant Encryption of JPEG2000 Codestreams. (2004). 2004 International Conference onImage Processing ICIP: 24-27 October, Singapore: Proceedings. 3439-3442. Research Collection School Of Information Systems.Available at: https://ink.library.smu.edu.sg/sis_research/535COMPLIANT ENCRYPTION OF JPEG2000 CODESTREAMSYongdong Wu and Robert H. DengInstitute for Infocomm Research21, Heng Mui Keng Terrace, Singapore, 119613{wydong, deng}@i2r.a-star.edu.sgABSTRACTThis paper presents a compliant encryption method for JPEG2000 codestreams such that the encryption process does notintroduce superfluous JPEG2000 markers in the protectedcodestream, i.e., the protected codestream preserves the syn-tax of the original codestream. The proposed encryptionmethod works with any standard ciphers, incurs no stor-age overhead, introduces negligible computational cost andmaintains all the desirable properties of the original JPEG2000 codestream such as error resilience and scalability.1. INTRODUCTIONJPEG2000 [1] is the latest international still image compres-sion standard. JPEG2000 Security (or JPSEC in short) isPart 8 of the JPEG2000 standard. One major technical issuein JPSEC is encryption (e.g., for codestream access controland confidentiality protection). A JPEG2000 codestream iscomposed of markers and data packets. The markers, withvalues restricted to the interval [0xFF90, 0xFFFF], are usedto delimit various logical units of the codestream, facilitatesrandom access, and maintains synchronization in the eventof error-prone transmission. The packets carry the contentbitstreams whose codewords (i.e., two contiguous bytes) arenot in the interval [0xFF90, 0xFFFF]. Since the output of agood cipher appears ”random”, straightforward applicationof a cipher to encrypt codestream packets is bound to pro-duce encrypted packets which include superfluous markers.Such markers will cause potentially serious decoding prob-lems (such as loss of codestream synchronization and erro-neous or faulty image transcoding). To overcome the su-perfluous marker problem, the encryption method must beJPEG2000 codestream syntax compliant. Such a compli-ant encryption method does not introduce superfluous mark-ers in the encrypted packets and maintains all the desirableproperties of the original codestreams.Zeng et al. [2][3] selectively shuffle MPEG streams us-ing shuffling tables so as to maintain syntax compliance.This shuffling method was generalized to index mapping in[4]. However, the schemes in [2]-[4] are not applicable toJPEG2000 codestream because the shuffling tables are toolarge to be implemented in practice.A syntax-aware encryption scheme was proposed by Wuand Mao [4]. This scheme applies bit stuffing in conjunc-tion with selective bitstream encryption to overcome the su-perfluous marker problem. However, bit stuffing not onlyincurs some storage overhead, but also leads to additionalwork for updating packet headers.Conan et al. [5] described a technique which selectivelyencrypt JPEG2000 codestreams in order to generate compli-ant encrypted codestreams. In this scheme, if any byte, sayX , has a value less than 0xF0, the four LSBs (Least Signif-icant Bits) of X are encrypted with a block cipher. Clearly,the security of this simple scheme is weak.Wu et al. [6] introduced a word-level encryption schemeemploying a stream cipher without scarifying the strengthof security. It encrypts packets in a codestream using arith-metic addition-module operation, rather than the standardXOR-module operation. However, the scheme producesonly partial compliant protected codestreams.Canon inc. proposed another word-level scheme [7]which encrypts a word recursively until the ciphertext iscompliant. This scheme not only has to check the valueof the current encrypted word, but also its proceeding byteand succeeding byte. Ma et al [8] pointed out that Canon’sproposal was not reversible, i.e., portion of a plaintext cannot be recovered from the corresponding ciphertext.Wu and Ma [9] proposed two packet-level encryptionschemes based on stream ciphers and block ciphers, respec-tively. They showed that the two schemes protect 99% ofa codestream. However, the schemes are not able to regainsynchronization when a byte is changed into 0xFF or whenpart of the packet is lost.This paper presents a codeblock-level compliant schemewhich independently encrypts Codeblock Contribution toPackets (CCPs) using standard ciphers. Our scheme pro-vides full protection of codestreams and allows direct ma-nipulation of the codestreams at the granularity of code-blocks. In addition, the protected codestreams inherit all thedesirable properties of the original JPEG2000 codestreams,e.g., error resilience and scalability.The rest of this paper is organized as follows. Section2 briefs the structure of JPEG2000 packets. Section 3 de-scribes our proposed compliant encryption scheme. Section4 analyzes the performance of the proposed scheme. Simu-lation results in Section 5 demonstrate the efficiency of theproposed scheme. A conclusion is drawn in Section 6.2. JPEG2000 PACKET STRUCTUREIn JPEG2000 standard [1], a tile-component of an origi-nal image or its lower resolution is decomposed into LL,HL, LH and HH subbands, where LL is the lower resolu-tion used for further decomposing. Each subband includesmany codeblocks. The individual bit-planes of the quan-tized DWT (Discrete Wavelet Transform) coefficients in acodeblock are coded in one of the three coding passes: sig-nificance propagation, magnitude refinement, and cleanup.The basic content unit in a JPEG2000 codestream ispacket which is associated with a specific tile, layer, com-ponent, resolution and precinct. Each layer consists of anumber of consecutive bit-plane coding passes from eachcodeblock, including all subbands of all tile-components.Referring to Figure 1, a Codeblock Contribution to Packet(CCP) is explicitly signalled within the packet header, andCCPs in a packet body is arranged in the order of HL, LHand HH subbands. Additionally, an important restrictionimposed by the JPEG2000 standard is that the last byte of aCCP can never be 0xFF [10].HLtagLHtagHHtagHL code bytes LH code bytes HH code bytesPacket Header Packet BodyFig. 1. Packet Structure: Packet bodies include CCPs(Codeblock Contribution to Packet).3. THE COMPLIANT ENCRYPTION SCHEMEThe goal of a compliant encryption is to output a protectedcodestream whose length is the same as that of the inputcodestream, and any word in the output content bitstream isnot in the interval [0xFF90, 0xFFFF]. Our proposed schemeselects CCP as the processing unit because the end byte ofCCP is non-0xFF. Assume that the encryption engine sharesa secret key with the decryption engine in advance. Thefollowing subsections elaborate how to adapt stream ciphersto generate compliant ciphertexts.3.1. Compliant EncryptionFigure 2 illustrates the process of encrypting a CCP P intoa compliant bitstream C. Assume that the CCP has a uniqueidentifier which is determined by tile, component, subband,etc, and P = {P1, P2, · · · , Pn} is of n bytes. The encryp-tion process proceeds as follows:(1) Generate key stream K of n bytes from the secret keyand CCP identifier with a stream cipher key generator.(2) Input P into the Microblock encryptor.(3) Compute C = P+K mod 256n = {C1, C2, · · · , Cn},where Ci is the ith byte, i = 1, 2, · · · , n.(4) Check whether C is syntax compliant. Specifically,for any i ∈ [1, n−1], if CiCi+1 ∈ [0xFF90,0xFFFF],C is non-compliant. In this case, let P ← C, and goback to step (2).(5) Check the last byte Cn. If Cn = 0xFF, C is non-compliant, let P ← C, and go back to step (2).(6) Output C as the compliant bitstream.KP={P1,P2,…,Pn}YesYesNoNoPlainbitstreamMacroblock   EncryptorCi Ci+1<0xFF90 ?Cn=0xFF?Compliant   ciphertext CKeystreamC={C1,C2,…,Cn} P        C P        CFig. 2. Diagram of Compliant Encryption.3.2. Compliant DecryptionThe decryptor parses a protected codestream into CCPs asthe encryptor does. For each CCP, the compliant decryptionis illustrated in Figure 3.(1) Generate the key K of n bytes from the shared key andCCP identifier using a stream cipher key generator.(2) Input bitstream C into the Microblock decryptor.(3) Compute bitstream P = C−K mod 256n = {P1, P2,· · · , Pn}, where Pi is the ith byte, i = 1, 2, · · · , n.(4) Check whether P is syntax compliant. Specifically,for any i ∈ [1, n−1], if PiPi+1 ∈ [0xFF90, 0xFFFF],(i = 1, 2, · · · , n− 1), P is non-compliant, let C← P,and go to step (2).(5) Check the last byte Pn. If Pn = 0xFF, P is non-compliant, let C ← P, and go to step (2).(6) Output P as the plaintext bitstream.KC={C1,C2,…,Cn}YesYesNoNoCipherbitstreamMacroblock   DecryptorPi Pi+1<0xFF90 ?Pn=0xFF?Original bitstream PKeystreamP={P1,P2,…,Pn} C        P C        PFig. 3. Diagram of Compliant Decryption.4. PERFORMANCE AND ANALYSIS4.1. RationaleIn the present scheme, CCP is encrypted recursively untilthe ciphertext meets two requirements:• any word (two contiguous bytes) is within [0, 0xFF90)• the end byte is not 0xFF.That is to say, a protected bitstream looks like a CCP. Ob-viously, this kind of protected bitstream is uniquely deter-mined with the minimal number of encryptions. Thus, theencryption process is reversible. On the other hand, anyCCP can be encrypted into a compliant bitstream.4.2. ScalabilityBecause the CCP is the processing unit, the packets in a pro-tected codestream can be re-organized with any progressiveorders. The protected codestream can also be processed atthe granularity of codeblocks without going through any en-coding again. Therefore, the present scheme maintains thescalability of the original JPEG2000 codestream.4.3. Error ResilienceIn a JPEG2000 codestream, an error in one coding pass willpropagate to the rest of the coding pass bitstream. In thepresent scheme, because the processing is CCP oriented, anerror is limited to the damaged CCP only. Thus, the presentscheme maintains the error-resilience of JPEG2000.4.4. Computational CostBecause encryption is regarded as a randomization opera-tion, the probability p of generating a compliant bitstreamwith one macroblcok encryption isp > pn0 = (255256)n,where p0 is the probability that one byte is not 0xFF. Thesolid line in Figure 4 illustrates the probability of generat-ing a compliant bitstream. Let q = 1 − p. Because therounds of encryption are independent, the expect number ofencryption for a compliant bistream isEn = p+ 2qp+ 3q2p+ · · · =+∞∑r=0(r + 1)qrp =1pThe dashed line in Fig. 4 shows the upper boundary of En.The JPEG2000 standard defines the size of a code-blockas no more than 4096 bits per bitplane. Thus the maximumsize of a CCP is 4096α bits where α is the number of bit-planes. In fact, the size of a CCP is usually small due to theunderlying efficient compression algorithm and layer seg-mentation. Because encryption operation is merely arith-metic module addition, and the key stream is generated onlyonce, the computational cost is very small.4.5. VariantAlthough stream ciphers are exemplified in the above mi-croblock encryption/decryption, block ciphers are applica-ble too. Technically, assume the size of employed blockcipher is b, and the size of bitstream P is n, then ECB mode(chapter 9 of [11]) of the block cipher is selected for en-crypting the first b × bn/bc bytes, and the aforementionedstream cipher is selected for encrypting the rest of the bit-stream P.5. SIMULATIONSThe sizes of CCPs vary from codeblocks, packets, and im-ages. In this simulation, 5000 compliant bitstreams are usedas test examples. The key stream is generated using RC4(Chapter 17 of [11]) . The number of repeated encryption(arithmetic addition module) is shown in Table 1. In Table1, the first column is the size of CCP in bytes, the other50 100 150 200 250 300 350 400 450 5000.10.20.30.40.50.60.70.80.91bitstream ( n bytes)   Success Probability  p50 100 150 200 250 300 350 400 450 50012345678#Expected Encryption  En Fig. 4. Solid line: Success probability (lower boundary) ofMacroblock encryption vs. bitstream size. Dash line: thenumber (upper boundary) of expected Macroblock encryp-tion vs. bitstream size.columns represent the percentage of repetitions for gener-ating protected compliant bitstreams. Table 1 indicates thatthe small number of repetitions is of high probability.Table 1. Percentage of encryption for generating a compli-ant bitstream.CCP size 1 2 3 4 >48 96.5 0.1 3.4 0.0 0.058 69.6 22.1 7.5 0.8 0.1108 65.3 23.0 9.9 1.5 0.3158 61.2 25.6 10.8 1.9 0.5208 55.9 29.0 10.9 3.2 1.0258 52.1 30.6 11.7 3.9 1.7308 49.3 31.7 12.7 4.5 1.9358 48.0 29.1 9.8 8.3 4.8408 44.8 29.3 10.6 6.6 8.6458 43.0 28.2 11.8 7.4 9.66. CONCLUSIONJPSEC focuses on the security aspect of JPEG2000 code-streams and files. Encryption is one of its main concerns.However, straightforward encryption may generate super-fluous markers in the protected codestreams. The compli-ant encryption method proposed in this paper overcomes theproblem using the standard ciphers and keeps the structureof the codestream. The proposed method also provides fullprotection of the codestream, maintains all the nice proper-ties of the original JPEG2000 codestream, such as error re-silience and scalability. We believe that the basic principlepresented here can be applied to encrypt other data formats,such as MPEG.7. REFERENCES[1] “Information Technology - JPEG 2000 Image Cod-ing System”, ISO/IEC International Standard 15444-1, ITU Recommendation T.800, 2000[2] Jiangtao Wen, M. Severa, Wenjun Zeng, M.H. Luttrelland Weiyin Jin, “A Format-compliant ConfigurableEncryption Framework for Access Control of Video,”IEEE Transactions on Circuits and Systems for VideoTechnology, 12(6):558-565, 2002[3] Wenjun Zeng, Jiangtao Wen, M. Severa, “Fast Self-synchronous Content Scrambling by Spatially Shuf-fling Codewords of Compressed Bitstreams,” ICIP, pp.III 169-172, 2002.[4] Min Wu and Yinian Mao, “Communication-friendlyEncryption of Multimedia,” IEEE Workshop on Mul-timedia Signal Processing, pp. 292-295, 2002[5] Vania Conan, Yulen Sadourny and Ste`ve Thomann,“Symmetric Block Cipher Based Protection: Con-tribution to JPSEC,” ISO/IEC JTC 1/SC 29/WG1N2771, Oct. 2003[6] Yongdong Wu, Robert Deng and Di Ma, “ImAccess:AMethod for JPEG 2000 Access Control,” Presentationon 29th ISO/IEC JTC 1/SC 29/WG1 meeting, Seoul,Mar. 2003,[7] Canon inc. “Encryption Tool for JPEG2000 AccessControl,” ISO/IEC JTC 1/SC 29/WG1 N2893, 2003[8] Di Ma, Yongdong Wu and Robert Deng, “Analysisof Canon Encryption Scheme,” Communications inJPEG2000 Security group (JPSEC), Nov. 14, 2003[9] Hongjun Wu and Di Ma, “Efficient and Secure En-cryption Schemes for JPEG2000,” ICASSP 2004,pp. V869-872, see also ISO/IEC JTC 1/SC 29/WG1N2937, 2003[10] D. S. Taubman and M. W. Marcellin, JPEG2000 - Im-age Compression Fundamentals, Standards and Prac-tice, Kluwer Academic Publishers, pp.495, 2001.[11] Bruce Schneier, Applied Cryptography: Protocols, Al-gorithms, and Source Code in C, 2nd edition, John Wi-ley & Sons, ISBN: 0471117099, 1995View publication stats

Compliant Encryption of JPEG2000 Codestreams

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Compliant Encryption of JPEG2000 Codestreams

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