An Experimental Study on Energy Consumption of Video Encryption for Mobile Handheld Devices Kyoungwoo Lee, Nikil Dutt, and Nalini Venkatasubramanian Center for Embedded Computer Systems Donald Bren School of Information and Computer Sciences University of California, Irvine <kyoungwl, dutt, nalini>@ics.uci.edu http://forge.ics.uci.edu/

Introduction Motivation Problem Mobile multimedia applications are vulnerable to security attacks in wireless networks Significant computation for video encryption is expected on battery-operated mobile devices Problem Evaluate symmetric video encryption schemes from the perspective of energy consumption both analytically and experimentally

Secure Video Application Battery -Operated Devices Raw Video Video Encoder Motion Estimation Quantization DCT Entropy Encoding Attacks Compressed Bit Stream Insecure network Symmetric Encryption Technique Encrypted & Compressed Bit Stream Secure Video Encoder Video Decoder Battery -Operated Devices This is the general block diagrams of video encoder and video decoder. Usually video encryption is done after encoding and video decryption before decoding. Here are typical secured video conferencing steps. But some algorithms such as Zig-Zag permutation is applied between quantization and entropy encoding in Encoder. Entropy Decoding Inverse Quantization IDCT Motion Compensation Compressed Bit Stream Decompressed Bit Stream Symmetric Decryption Technique Encrypted & Compressed Bit Stream Secure Video Decoder

Video Encryption Schemes Naïve Encryption Scheme Selective Encryption Scheme Zig-Zag Permutation Scheme Video Encryption Algorithm (VEA) Symmetric Encryption Technique The same encryption technique and the same security key are used to encrypt and decrypt the message (e.g. – DES and AES) A Secret Message #P(&*(UV +*#$@JH} Encrypt Decrypt plaintext ciphertext network Briefly I’ll review video encryption algorithms and compare them. They are Naïve Algorithm, Selective Algorithm, Zig-Zag Permutation Algorithm, Video Encryption Algorithm, and sign-bit Encryption Algorithm.

Studied Video Encryption Schemes (1) Naive Encryption Scheme I-frame P-frame Naive Encryption (DES) Video Encoding (H.263) EnergyNaive=eDES*STotal eDES - energy to encrypt one byte by DES STotal - size of the whole video data EnergySelective = eDES*SIB SIBl - size of Intra-blocks in video data Intra-block I-frame P-frame Selective Encryption (DES) Video Encoding (H.263) (2) Selective Encryption Scheme Naïve Algorithm encrypts the entire video streams like a text. This is very secure but slow comparing with others. But the size of encrypted video stream doesn’t change like other algorithms.

Studied Video Encryption Schemes (cont’) EnergyZig-Zag = eoverhead eoverhead - energy to shuffle coefficients I-frame P-frame Video Encoding & Zig-Zag Permutation (H.263 & Shuffle) (3) Zig-Zag Permutation Scheme eXOR - energy for XOR EnergyVEA = ½*(eDES+eXOR)*STotal I-frame P-frame VEA (XOR & DES) Video Encoding (H.263) (4) Video Encryption Algorithm (VEA)

Comparison of Video Encryption Schemes Analytical Comparison Algorithm Drawback Relative Energy Naive Significant Computation 100 % Selective Moderate Security 59 % Zig-Zag Breaks efficiency of Video Encoding < 1 % VEA Not applicable for H.263 without even distribution 50 % Naïve encryption scheme consumes twice the energy of Selective encryption scheme

Power Measurement System Experimental Setup Experimental Setup System Architecture PZaurus = * VZaurus VR R Secure Video Application (Encoder / Decoder) DES H.263 Codec Device Driver 5 V V Zaurus OpenSSL Library R = 22 ohm Operating System (Linux) V R Mobile Handheld Hardware (Sharp Zaurus) DAQ board with BNC Connector Windows XP 1,000 samples/sec 400 MHz Intel XScale 64 MB flash & 32 MB SDRAM Power Measurement System

Energy Consumption for Varying Quality and Security (Quant Scale) Security (Full vs. Partial) Measured Energy (J) Energy Overhead High (Quant = 1) High (Full) 128.2 13 % Low (Partial) 111.0 Mid-High (Quant = 4) High (Full) 92.05 9 % Low (Partial) 83.56 Mid-Low (Quant = 10) High (Full) 77.62 2 % Appropriate for mobile video Low (Partial) 75.78 Low (Quant = 31) High (Full) 70.44 1 % Low (Partial) 69.89 Energy overhead for full encryption is NEGLIGIBLE

Experimental Results: Video Coder & Crypto 80 74.77 70 60 Huge Difference (98 %) 50 Measured Energy (Joules) 40 30 20 11.37 10 1.5 Application H.263 Encoder H.263 Decoder DES Crypto Encryption consumes negligible energy as compared to encoding

Experimental Results: Video Encryption Negligible Energy Overhead 90 77.62 80 74.77 75.78 72.87 74.11 72.26 (2.4%) 70 (1.7%) 60 Measured Energy (Joules) 50 Encoding without Encryption 40 Encoding with Encryption (Selective) Encoding with Encryption (Naïve) 30 20 10 FOREMAN.qcif NEWS.qcif 11 MB with 300 frames 1:10(IP ratio),10(Quant),full search Video Clips Energy consumption of encryption is negligible irrespective of video clips