The USC Andrew and Erna Viterbi School of Engineering USC Signal and Image Processing Institute USC Ming Hsieh Department of Electrical Engineering University of Southern California

Technical Report USC-SIPI-368

“Light-Weight Multimedia Encryption: Algorithms and Performance Analysis”

by Dahua Xie

May 2004

Efficient and secure encryption methods for multimedia content protection are studied in this research. Two new encryption methods, namely the randomized entropy coding (REC) and random rotation in partitioned blocks (RPB), have been proposed. In the REC encryption scheme, an entropy coder is equipped with multiple coding parameters. Encryption is done by randomly choosing one coding parameter according to a pseudo-random sequence to encode consecutive inputs. The RPB encryption scheme exploits the almost redundancy-free characteristics of the coded multimedia bit stream. The bit stream is partitioned into random-sized blocks and a random rotation in each block is performed to achieve encryption. Both the REC and RPB methods have low encryption cost and can be easily implemented in most multimedia coding systems. Both of them achieve the security strength that is between the stream cipher and the block cipher.

This research also investigates distortion-aware multimedia content authentication. A new hash function, called the distance-preserving (DP) hash function is developed to alleviate the hard authentication problem of the traditional hash function. Under the same secret key, two DP hash-values reveal the distance between corresponding preimages. If data have been modified during transmission, this distance provides valuable information about the error and allows distortion evaluation. Properties and security strength of the DP hash function are investigated. A general framework for distortion-aware multimedia authentication based on the DP hash function is outlined.

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