Joint Compression and Encryption of
JPEG2000 Images
A Thesis Submitted to Chongqing University
in Partial Fulfillment of the Requirement for the
Master’s Degree of Engineering
By
大民3307Yu Chenyun
Supervised by Ass. Prof. Xiang Tao
Specialty: Computer Software and Theory
College of Computer Science of
Chongqing University, Chongqing, China
April, 2014
摘要
随着物联网的兴起与应用，越来越多的多媒体数据在无线多媒体传感器网络中传输。由于传感器节点通常部署在公共环境中，容易受到窃听与篡改，其安全性受到严重威胁。WMSN具有能量敏感性，要求实时传输并且要满足Qos要求，传统的加密算法无法适用于该网络中的应用与服务。为了提高处理效率，需要把加密与压缩结合起来。JPEG2000是当前性能突出的压缩标准，在低比特率传输条件下仍然具有较高的压缩率，因此，该压缩算法在WMSN中具有广阔的应用前景。
基于压缩编码的加密方式将加密嵌入压缩过程，不仅能减少计算负载，还能够保持良好的压缩性能。选择加密，是针多媒体信息特点的一种“量身定做”的加密方案。它的基本思想是：通过选择性地加密一些被定义为“重要”的数据来减少加密数据量。由于只有部分数据被加密，相应的时间开销将显著减少。因此，本文的工作重点是：结合JPEG2000的编码过程设计加密算法，尽可能地在提高加密效率的同时保持格式兼容性并适应WMSN中的实时传输。 ANALYSISES首先，本文介绍了密码学、数字图像加密的基础知识和相关理论并深入研究JPEG2000压缩算法。通过分析比较现有的各种加密算法的优缺点得出了本文的工作重点：设计与JPEG2000编码过程相结合的图像加密算法。
其次，在介绍算术编码的基础上重点分析了基于区间交换加密算法的安全性，然后提出了一种针对这种加密的攻击方法。安全性分析表明：基于区间交换的算术编码存在安全性问题，在结合JPEG2000的MQ编码器设计加密算法时应当考虑从加密编码参数或者改变区间计算的角度设计加密方案。
蒲剧苏三起解最后，本文在安全性分析的基础上结合MQ编码过程提出了一种选择加密方案SMQ：通过安全地改变MQ编码器的概率估计表将加密操作嵌入到JEPG2000的编码过程中。与其他的选择加密方案不同，该算法所加密的数据是固定的，不论图像有多大，仅仅只有概率估计表中的47个Qe值被加密。因此，该算法特别适用于加密WMSN中的JEPG2000图像，尤其是在处理大数据图像时具有明显优势。理论分析和实验结果表明该算法在保持良好压缩性能与低能耗的同时能够实现安全性与加密效率的平衡。
关键词：JPEG2000，MQ 编码器，选择加密，WMSN
ABSTRACT
With the rapid developenment and widespread applications of WSN, more and more multimedia data are transmitted in WMSN. As sensor nodes usually are deployed in public environment, they are under various threats, such as wiretapping and tampering. Because of energy sensitivity, requirements for Qos service and realtime transmission, traditional encryption algorithms can not be suitable for the applications and services in WMSN. To improve processing efficiency, encryption is suggested to combine with compression. Currently, JPEG2000 is an outstanding compression standard, especially the excellent compression rate in low-bit rate transmission. Therefore, JPEG2000 presents broad application prospects in WMSN.
Joint compression and encryption can embed encryption operations into the process of image compression. Since the processes of data encryption and data compression are combined into single one, the computational overhead can be saved; meanwhile, the compression performance could be well maintained by careful design. Selective encryption is a specific scheme for multimedia data. Its basic idea is reducing the amount of data to be encrypted by selectively encrypting a part of
data which is defined as important. Because only partial data are encrypted, the time overhead of encryption can be significantly reduced. Hence, our focus is designing encryption algorithm combining with JPEG2000compression process to improve operation speed and support real-time transmission.
At first, this thesis introduces basic knowledge and theories about cryptography, encryption for digital images and JPEG2000 compression standard. Through analyzing and comparing different encryption algorithms, we step into the work about designing joint compression and encryption algorithms for JPEG2000 images.
Then, this paper proposes an attack method for interval swapping encryption in arithmetic coding. Because of vulnerability, Security analysis suggests that interval swapping should be avoided when designing encryption algorithm joint with MQ encoding in JPEG2000. Other ideas also can be consided, such as parameters encryption and changing intervals calculation.
Finally, a selective encryprion method joint with MQ coding is proposed basing on security analysis, which is called secure MQ coder (SMQ). It embeds encryption into JPEG2000 coding by securely changing the probability estimation table for MQ coder.
沈阳市装备制造工程学校
Different from most existing selective encryption algorithms, the volume of selectively encrypted data is constant. As only 47 Qe are encrypted regardless of the size of whole image, the algorithm is extremely fast and suitable for protecting JPEG 2000 images in WMSNs, especially for huge digital images. Theoretical analysis and experimental results show that the algorithm can achieve balance between security and efficiency, while keeping good compression performance and a small amout of energy consumption
Keywords：JPEG2000, MQ coder, selective encryption, WMSN
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重庆大学硕士学位论文目录
目录
中文摘要.......................................................................................................................................... I 英文摘要........................................................................................................................................ II 1 绪论 . (1)
1.1研究背景及意义 (1)
1.2 国内外研究现状 (2)
1.3 研究内容与论文组织 (3)
2 密码学及数字图像加密技术 (4)
2.1密码学简介 (4)
2.1.1密码系统基本模型 (4)
2.1.2 密码系统的分类 (4)
2.2.3 密码系统安全性评价标准 (6)
2.2.4 密码分析学 (6)
2.2 数字图像特点及其加密技术 (7)
2.2.1 数字图像特点 (7)
2.2.2 数字图像加密技术 (7)
2.3 本章小结 (9)
3 JPEG2000编码标准及其加密技术 (10)
3.1引言 (10)
3.2 JPEG2000内容及性能特点 (10)
3.3 JPEG2000的应用 (11)企业家天地杂志社
3.4 JPEG2000编码过程 (11)
3.4.1预处理 (12)
3.4.2离散小波变换 (13)
3.4.3量化过程 (13)
3.4.4位平面编码 (14)
3.4.5 MQ编码 (22)
3.4.6码流装配 (26)
3.5 与JPEG2000相结合的加密技术 (27)
3.6本章小结 (29)
4针对区间交换算术编码的攻击方法 (30)
4.1算术编码基本原理 (30)
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