Energy Consumption of Video Encryption for Mobile Devices: An Experimental Study

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

2. Contents • Introduction of Video Encryption • Video Encryption Algorithms • Experiments • Conclusion and Issues

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

4. Secure Video Conferencing Video Encoder Motion Estimation DCT Quantization Entropy Encoding Raw Video Battery -Operated Devices Insecure network Compressed Bit Stream Symmetric Encryption Technique Secure Video Encoder Encrypted & Compressed Bit Stream Attacks Video Decoder Battery -Operated Devices Entropy Decoding Inverse Quantization IDCT Motion Compensation Compressed Bit Stream Decompressed Bit Stream Symmetric Decryption Technique Secure Video Decoder Encrypted & Compressed Bit Stream

5. 2. Video Encryption Algorithms • Naïve Algorithm • Selective Algorithm • Zig-Zag Permutation Algorithm • Video Encryption Algorithm • Sign-Bit Encryption Algorithm • Analytical Comparison

6. 2. Video Encryption Algorithms (0) Symmetric Encryption Technique (DES) 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 A Secret Message #P(&*(UV +*#$@JH} #P(&*(UV +*#$@JH} network Encrypt Decrypt plaintext ciphertext ciphertext plaintext

7. 2. Video Encryption Algorithms- 1) Naïve Algorithm Video Encoding (H.263) NAÏVE Encryption (DES) P-frame P-frame I-frame P-frame P-frame I-frame • Encrypt the entire MPEG stream • Most secure MPEG encryption algorithm because there is no effective algorithm to break DES • Slow • Size of the encrypted stream does not change

8. 2. Video Encryption Algorithms- 2) Selective Algorithm • Use the features of MPEG layered structures • Aegis • Encryption of I frames • Encryption of MPEG video sequence header • Encryption of ISO end code • Agi and Gong • Great portions of video are visible • partly because of inter-frame correlation • mainly from unencrypted I blocks in the P and B frames • In addition, encryption of all I blocks in P and B frames • Encrypting only I frames can save 30-50 of encryption/decryption time • Increase the frequency of I frames • increase the length of string and consequentially the encryption time. • SECMPEG : Meyer & Gadegast • A new MPEG-like bitstream  special encoder/decoder required • 4 secure level • Headers • Headers, CD coefficients & lower AC terms of I blocks • I frames and I blocks • All data • Not safe • Encryption of only I frame  visible partly because of inter-frame correlation mainly from unencrypted I blocks in the P and B frames • Encryption of headers  (1) mostly standard information such as frame starting code, frame size (2) MPEG stream is indexed by frame

9. 2. Video Encryption Algorithms- 2) Selective Algorithm (cont’) Video Encoding (H.263) SELECTIVE Encryption (DES) P-frame P-frame I-frame P-frame P-frame I-frame Intra-block

10. 2. Video Encryption Algorithms- 3) Zig-Zag Permutation Algorithm • Two levels of security to digital image • obscured image • incomprehensible image • Basic Idea • use a random permutation list to map the individual 8x8 block to a 1x64 vector • Generate a random permutation list • Split DC coefficient and one of them is saved at the least AC coefficient • Apply the permutation list to the split block • Tang (CMU) • DC coefficient is mapped to the first element in the 1x64 vector and the rest of the elements are permuted.  Obscured image • DC coefficient of every bock is set to zero or a fixed value between 0 and 255 and rest of the elements are permuted.  Obscured image • DC coefficient is mapped to any other position other than the first position in the 1x64 vector, and the rest of the elements are randomly permuted  Incomprehensible image • AC63 coefficient is set to 0  Degradation is negligible • Split the DC coefficient into two parts, first part remain in the same position, the second part is substituted for AC63 and randomly permute the list  Incomprehensible image • Vulnerable to the cyphertext attack: Statical analysis(Qiao and Nahrstedt) • binary coin flipping sequence together with two different permutation lists • Subject to the plain text attack • Not satisfying security • Plaintext attack • Cyphertext attack

11. 2. Video Encryption Algorithms- 3) Zig-Zag Permutation Algorithm (cont’) Video Encoding & Zig-Zag Permutation (H.263 &Shuffle) P-frame P-frame I-frame

12. 2. Video Encryption Algorithms- 4) Video Encryption Algorithm Video Encoding (H.263) VEA (XOR & DES) P-frame P-frame I-frame P-frame P-frame I-frame • Qiao and Nahrstedt (UIUC) • Based on statistical properties of MPEG stream : Uniform distribution of streams • faster(47%) than DES because DES is used on partial bit stream • Immune to plain-text attack & cypher-text attack • Algorithm • Choose odd-numbered bytes and even numbered bytes. • XOR the two streams a1,a2… a2n-1 XOR a2,a4… a2n c1,c2… cn • Choose an encryption function E (DES ) to encrypt a2,a4… a2n resulting cipher-text has the form c1,c2… cn E(a2,a4… a2n) • If a2a4…a2n has no repeated pattern, then the secrecy depends on function E because a2a4…a2n is one-time pad well know to be perfectly secure

13. 2. Video Encryption Algorithms- 4) Video Encryption Algorithm (cont’) • All tests on the different MPEG streams show similar statistical results Frequency of Occurrence of Byte Values (The distribution of MPEG stream vs English) Frequency of Occurrence of Byte Values (The distribution of different MPEG streams

14. 2. Video Encryption Algorithms- 4) Video Encryption Algorithm (cont’) • It is not applicable since byte-values are not uniformly distributed in case of H.263 encoded video stream

15. 2. Video Encryption Algorithms-5)Sign-Bit Encryption Algorithm • Shi & Bhargava (Purdue) • selective encryption scheme which operates on the sign bits of DCT coefficient of a MPEG compressed video • much more efficient than DES because it selectively encrypts the MPEG stream • Light-weight and cost-effective • Encryption function • Ek(S)=…(b1 XOR s1) …(bm XOR sm)(b1 XOR sm+1)…(bm XOR s2m)… • Where s1s2…smsm+1…s2m…are all of the sign bits of DC and AC coefficients and the key k=b1b2….bm is a randomly generated bit stream of length m • A more effective modification • use a secret key randomly changing the sign bits of differential values of DC coefficients of I frames and the sign bits of differential values of motion vectors • very efficient in terms of computational complexity because it omits the encryption of AC coefficients altogether • because DC coefficients and AC coefficients are related DC coefficients may be derived from AC coefficients for an attack • Secure Level • Encrypting all motion vectors of P frames and B frames • Encrypting all DC coefficients of I frames • Encrypting all DC coefficients of I frames and all motion vectors of P frames & B frames

16. 2. Video Encryption Algorithms-5)Sign-Bit Encryption Algorithm (cont’) Obscured but Comprehensible Blurred but Comprehensible incomprehensible

17. Comparison of Energy Consumption • Definition of the Size • ST size of total encoded bit stream in Byte • SI size of I frames in total encoded bit stream in Byte • SP size of P frames in total encoded bit stream in Byte • Sib_size of I blocks in SP in Byte • SH size of Headers in total encoded bit stream in Byte • ST = SI + SP + SH • Definition of amount of Energy Consumption • eDES amount of energy consumption to encrypt 1 Byte plaintex using DES(Data Encryption Standard) • Ealgorithm amount of energy consumption to total bit stream using algorithm • Eencoding amount of energy consumption to encode the video file

18. Comparison of Energy Consumption • Naïve Algorithm • ENaive = eDES * ST • Selective Algorithm • Encryption of I frames • ESel_I = eDES * SI • ESel_I = 0.5 * ENaive because SI is b/w 30% & 60% of ST • Encryption of I frames and I blocks in P frames • ESel_I+ib = eDES * ( SI + Sib ) + eoverhead • Where eoverhead is amount of energy consumption to detect I blocks • ESel_I+ib = 0.6 * ENaive + α because Sib is b/w 10% & 40% of SI

19. Comparison of Energy Consumption (cont’) • Zig-Zag Permutation • Basic • EZZ_basic = 0 * ENaive + α • where α is the energy consumption for split & permutation • However Eencoding increases (similar to decrease Quantization value, ex: Q=10  Q=4) • Encryption of DC coefficients group • EZZ_DC = EZZ_basic + {(# of blocks per frame)*(# of frames in an encoded stream)*eDES} • Coin Flipping Sequence • EZZ_CFS = EZZ_basic + β • where β is almost zero

20. Comparison of Energy Consumption (cont’) • Video Encryption Algorithm • EVE = eDES *(½ * ST) + eXOR ≒ 0.5 * ENaive • where eXOR is amount of energy consumption for XOR computation∵½ • Sign-Bit Encryption Algorithm • ESB = ⅛ * SI *eXOR + δ • where eXOR is amount of energy consumption for XOR computation and δ is the energy overhead to extract sign-bits

21. Analyzing the Energy Consumption of Security Protocols The larger data size, the more energy consumption

22. Comparison of Energy Consumption - example eDES = 2.08 uJ, ST = 233,414 Bytes and Eencoding = 14.02 J in Foreman.263 when resolution = QCIF, Q = 10 & I:P = 1:9

23. 2. Video Encryption Algorithms- 6) Analytical Comparison * Analytical Expectation

24. 3. Experiments • Experimental Setup • Encoding/Decoding/Encryption • Video Encoding by H.263 with Naïve Video Encryption by DES • Video Encoding by H.263 with Selective Video Encryption by DES • Video Decryption by DES & Video Decoding by H.263

25. 3. Experiments- 1) Experimental Setup National Instruments Power Measurement Device Windows 2000 Advanced Server Desktop PC getpower Linux / Arm 400 MHz Sharp SL-5600 H.263 Coder / DES Crypto • Experimental Architecture

26. 3. Experiments- 1) Experimental Setup (cont’)

27. 3. Experiments- 1) Experimental Setup (cont’) Experimental Environments

28. 3. Experiments- 1) Experimental Setup (cont’) • Experimental Procedure

29. 3. Experiments- 1) Experimental Setup (cont’) • Experimental Method Measured Power Average Active Power Measured Total Energy Active Energy Idle Energy Power Time Average Idle Power Total Execution Time

30. 3. Experiments- 1) Experimental Setup (cont’) Experiments • Individual Application • (S1) Video Encoder (H.263) • FOREMAN.qcif w/ 300 frames • of 11MB • 1:10 (IP ratio), 10 (Quant), Full • Search • (S2) Video Decoder (H.263) • Variable encoded bit streams • 233 KB with default • (S3) Crypto Application (DES) • 233 KB of encoded bit stream • Integrated Application • (I1) Encoder with Full Encryption • Integrate (S1) and (S3) • Variable Quant & fixed others • (I2) Encoder with Partial • Encryption • Integrate (S1) and (S3) • to encrypt only Intra-blocks • with the same parameters • (I3) Decoder with Full Decryption • - Integrate (S2) and (S3)

31. 3. Experiments- 1) Experimental Setup (cont’) • Definitions • Total Execution Time (second): total time to execute encoding, decoding or encryption on Zaurus • Measured Total Energy (Joule): Total Execution Time * Measured Power[= Pactive-Pidle] • Energy Consumption per byte (uJoule): Measured Total Energy / size of input file • Energy Consumption per second (Watt): Power = Measured Total Energy / Total Execution Time = Measured Power • Ratio(%): Encryption Energy Overhead = 100 * (Energy Consumption for Encoding with Encryption / Energy Consumption for Encoding)

32. 3. Experiments- 2) Encoding/Decoding/Encrypt Input file: FOREMAN.qcif (11,404,800 bytes) Encoder parameters: Q=10, IP ratio=1:10 and default parameters

33. 3. Experiments- 3) Video Encoding & Encrypt

34. 3. Experiments- 3) Video Encoding & Encrypt (cont’) 80 74.77 70 60 Huge Difference (98 %) 50 Measured Energy (Joules) 40 30 20 11.37 10 1.5 0 Application H.263 Encoder H.263 Decoder DES Crypto

35. 3. Experiments- 3) Video Encoding & Encrypt (cont’) Negligible Energy Overhead 90 77.62 75.78 74.77 80 74.11 72.87 72.26 (2.4%) 70 (1.7%) 60 Encoding without Encryption 50 Measured Energy (Joules) Encoding with Encryption (Selective) 40 Encoding with Encryption (Naïve) 30 20 10 0 FOREMAN.qcif NEWS.qcif Video Clips

36. 3. Experiments- 3) Video Encoding & Encrypt (cont’)

37. 3. Experiments- 4) Naïve & Selective Encryption

38. 3. Experiments- 4) Naïve & Selective Encryption (cont’)

39. 3. Experiments- 5) Video Decrypt & Decoding

40. 3. Experiments- 6) Quality and Security Level

41. 3. Experiments- 6) Quality and Security Level (cont’)

42. 3. Experiments- 6) Quality and Security Level (cont’)

43. 3. Experiments- 6) Quality and Security Level (cont’)

44. 3. Experiments- 6) Quality and Security Level (cont’)

45. 3. Experiments- 6) Quality and Security Level (cont’) • Other Parameters to effect on QnS Level • Resolutions • Decoding Side • Number of Users • Others

46. 4. Conclusion and Issues • Conclusion • Issues • Next Step

47. 4. Conclusion and Issues- 1) Conclusion • Energy Consumption for Video Encryption is not a big deal comparing to that for Video Encoding • Energy Consumption for Video Decryption is critical • Energy for Video Encryption/Decryption increases with an increase of the encoded file size • Selective Algorithm is more energy-efficient but less secure than Naïve Algorithm

48. 4. Conclusion and Issues- 1) Conclusion (cont’) • High quality Encoding (eg: quantization) [low compression) • Increase energy consumption for encryption (∵usually high quality video encoding increases the file size) • Increase energy consumption for decoding • IP ratio (Naïve Video Encryption vs Selective) • Decrease IP ratio in Encoding (assumption: only encrypting I-frames) • Possible to decrease energy consumption • But we have to consider increase of energy in encoding & decoding and compare it with decrease of energy in encryption & decryption)

49. 4. Conclusion and Issues- 2) Issues • Ideas • Hybrid Video Encryption Algorithms • Main Idea: Encrypt I-frames and I-blocks in P-frames by Video Encryption Algorithm • We can reduce computation to half of Selective Algorithm • Assumption: Byte values in I-frames and I-blocks are even distributed

50. 4. Conclusion and Issues- 2) Issues (cont’)