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1 A video authentication scheme for H.264/AVC Main profile Nandakishore Ramaswamy Multimedia Processing Lab July 9 th, 2004.

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2 Agenda Objectives Introduction Previous work Encoder/Decoder description Simulation Results Conclusion and Future work References

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3 Objectives Verify the integrity of the video bitstream compressed by H.264/AVC Main Profile Identify the originator (sender) of the video

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4 Introduction Multimedia authentication: - Verify the integrity of the multimedia signal a) Hard authentication: - Allows no alteration of the pixel values. b) Soft authentication: - Accepts manipulations of the pixel values which preserve the semantic structure of the multimedia signal. Typically, cryptographic techniques are used for authentication and verification.

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5 Digital Signature Vs Encryption Digital Signature Alice wants to sign and send a message to Bob Encryption algorithm Bob Messages match Alice’s private key Digital Signature Alice’s public key Received Digital Signature Original Message Received Message Encryption algorithm Alice Yes = Signature Verified No= Signature Verification failed

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6 Digital Signature Vs Encryption (contd.) Encryption Alice wants to encrypt and send a message to Bob Encryption algorithm Bob Bob’s public key Cipher message Bob’s private key Received cipher message Original Message Encryption algorithm Alice

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7 Introduction (contd.) A generic video authentication process [1]

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8 Introduction (contd.) A generic video verification process [1]

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9 Digital Signature Standard Digital signature standard (DSS) a) Developed by NIST b) Consists of two parts - Secure Hash Algorithm (SHA) - Digital Signature Algorithm (DSA)

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10 (DSA and SHA)’s relationship Secure Hash Algorithm DSA Sign operation Secure Hash Algorithm DSA Verify Operation Signature Original Message Received Message Message Digest Private Key Public Key Yes = Signature Verified No= Signature Verification failed Signature Generation Signature Verification Source:- Federal Information Processing Standards Publications – bits 320 bits

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11 Rivest Shamir and Adleman (RSA) Encryption Let m = Input Message e = Encrypted message n = Common parameter pr = Private Key pb = Public Key Encryption e = m pr * mod(n) Decryption m = e pb * mod(n)

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12 Previous Work Digital signature generation using block means [2] Division into 8x8 blocks Block mean computation QuantizationEncryption Original Image Sender’s secret key Digital Signature

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13 Previous Work (contd.) Digital signature verification using block means [2] Division into 8x8 blocks Extract Block means before inverse quantization Decryption Block means match Received Image Received signature Image Authentic Image NOT Authentic Yes No Sender’s public key

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14 Previous Work (contd.) Digital signature in JPEG-2000 [3] Every code-block of the compressed image is hashed using Secure Hash Algorithm and appended at the end of the bitstream. JPEG-2000 code-block Compute hash using SHA Encrypt using RSA Sender’s public key 160 bit digest Append to bitstream For verification, received image’s code-blocks are hashed and matched with decrypted hash.

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15 Encoder/Decoder description A video authentication scheme for H.264/AVC Main profile

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16 Encoder Luma values only Features taken in transform domain Intra and Inter MB’s Signature for every coded video sequence

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17 Encoder (contd.) Intra 4x4 and Inter MB DCAC (0,0) (3,0) (0,3) (3,3) (3,0) (3,3) (0,3) (0,0) Q 4X4 integer DCT T Original residual block Transformed and quantized block Feature data

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18 Encoder (contd.) Intra 16x16 MB T Q T 4X4 integer DCT 4X4 Hadamard transform Original 16x16 MB residual Transformed 16x16 MB Quantized Hadamard coefficients Q Feature data

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19 Encoder (contd.) Collect all feature data of a MB for every picture. Insert picture number after a picture is coded Repeat process until end of sequence

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20 Encoder (contd.) Feature data Hash (SHA) Generate signature D=DSA(H) Encryption E= RSA(D) Sender’s private key Receiver’s public key Append as SEI to video bitstream Signature generation for a coded video sequence H D E

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21 Encoder (contd.) Multiple signature generation a) Video = 1 or more video sequences b) Generate signature for every video sequence c) Append every signature as SEI in the corresponding video sequence

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22 Decoder (contd.) Luma values only Features taken in transform domain Signature verification for every coded video sequence

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23 Decoder (contd.) Intra 4x4 and Inter MB’s DCAC (0,0) (3,0) (0,3) (3,3) 4x4 block of transform coefficients before inverse quantization Feature data

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24 Decoder (contd.) Intra 16x16 MB Transformed 16x16 MB before inverse quantization Hadamard coefficients before inverse quantization 15 AC coefficients Feature data

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25 Decoder (contd.) Collect all feature data of a MB for every picture. Insert picture number after a picture is decoded Repeat process until end of sequence

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26 Decoder (contd.) Signature verification for a coded video sequence Feature data Hash (SHA) Verify signature D’’ = DSV(H’,D’) Decryption D’=RSA -1 (E’) Received video and signature D’’= D’ Sender’s public key Receiver’s private key Video Authenticated Video NOT Authenticated E’ D’ D’’ H’ Yes No

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27 Decoder (contd.) Tampering frames = Signature failure Sender forgery = Signature failure Cannot point out the reason of signature failure If tampered, cannot point out location of tampering Modify encoder to accommodate these issues

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28 Revised Encoder Compute hash of every picture in the coded video sequence. Signature failure = Match decoder hash Inter and Intra for hash computation Transform domain values only Luma frames Authentication data = Signature + Hash

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29 Hash computation Intra 4x4 and Inter MB DCAC (0,0) (3,0) (0,3) (3,3) (3,0) (3,3) (0,3) (0,0) Q 4X4 integer DCT T Original residual block Transformed and quantized block Feature data

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30 Hash computation (contd.) Intra 16x16 MB T Q T 4X4 integer DCT 4X4 Hadamard transform Original 16x16 MB residual Transformed 16x16 MB Quantized Hadamard coefficients Q Feature data

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31 Hash computation (contd.) Feature data for a picture Hash P H = SHA(data) Encryption E H = RSA(P H ) Receiver’s public key Append as SEI to video bitstream Hash generation for a picture PHPH EHEH Repeat process for every picture in the coded video sequence

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32 Tampered locations and sender forgery Signature Failure Decrypt hashes Compute Hash for every picture All Hashes match? Signature failure due to sender forgery Signature failure due to tampering. ( Identify tampered locations) Receiver’s private key YesNo

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33 Decoder Hash Computation Intra 4x4 and Inter MB: - DC and AC coefficients of every 4x4 block before inverse quantization DCAC (0,0) (3,0)(3,3) (0,3) 4x4 block of transform coefficients before inverse quantization Feature data

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34 Decoder Hash Computation (contd.) Intra 16x16 MB Transformed 16x16 MB before inverse quantization Hadamard coefficients before inverse quantization 15 AC coefficients Feature data

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35 Simulation Results A video authentication scheme for H.264/AVC Main profile

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36 DSA common parameters Private Key Public Key

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37 Results for one coded video sequence Common Parameters Total frames encoded = 59 Total coefficients = Encoder signature r = s = Without tampering or forgery Decoder Signature v = Since r = v, signature is verified.

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38 Results for one coded video sequence (contd.) Frame tampering Frame 0 = I frame = tampered Location = 1 st Intra 16x16 block, DC coefficient at (0,0) after Hadamard transform and quantization Original value = 5 Modified value = 15 Decoder signature v = But r = Since, r is not equal to v, Signature is NOT verified.

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39 Results for one coded video sequence (contd.) Hash of all pictures in the video sequence are compared. Picture 0 Encoder Hash = Decoder Hash = Hashes are NOT equal. Tampered location = Picture 0

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40 Results for one coded video sequence (contd.) Detecting malicious activity Private key used to sign video = Imposter’s Public key used to verify = Legal user’s Original Private Key = Imposter’s private key =

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41 Results for one coded video sequence (contd.) Encoder signature r = s = Decoder signature v = Since r is NOT equal to v, signature is NOT verified. Encoder hashes = Decoder hashes Thus, signature failure due to malicious activity.

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42 Results for one coded video sequence (contd.) Robustness to quantization Sequence is encoded with QP 29 Encoder signature r = s =

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43 Results for one coded video sequence (contd.) Sequence is re-encoded with QP 35 Decoder signature v = Since r is NOT equal to v, Video is NOT authenticated.

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44 Results for one coded video sequence (contd.) Frame reordering attack Original Re-ordered

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45 Results for one coded video sequence (contd.) DC Attack : - Block mean kept the same but values modified. Original BlockTransformed BlockQuantized Block Modified BlockTransformed BlockQuantized Block TQ T Q

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46 Results for one coded video sequence (contd.) When using only DC coefficient Encoder Signature (Original Block) Decoder Signature (Modified Block) Video is authenticated (Signatures match) even though the block has changed!

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47 Results for one coded video sequence (contd.) When using DC and AC coefficients Encoder Signature (Original Block) Decoder Signature (Modified Block) Video is NOT authenticated. Robust to DC attack!

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48 Results for one coded video sequence (contd.) Encoder signature r = s = Decoder signature v = Since r is NOT equal to v, signature is NOT verified.

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49 Results for multiple coded video sequence (contd.) Total number of frames encoded = 59 Total number of video sequences = 6 Total number of signatures = 6 Encoder Signature 1 Total number of coefficients = 4334 r = s =

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50 Results for multiple coded video sequence (contd.) Encoder Signature 2 Total number of coefficients = 3724 r = s = Encoder Signature 3 Total number of coefficients = 3896 r = s = Encoder Signature 4 Total number of coefficients = 4561 r = s =

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51 Results for multiple coded video sequence (contd.) Encoder Signature 5 Total number of coefficients = 4020 r = s = Encoder Signature 6 Total number of coefficients = 3860 r = s =

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52 Results for multiple coded video sequence (contd.) Decoder Signatures v i = Signature for i th video sequence v 1 = v 2 = v 3 = v 4 = v 5 = v 6 = Signatures match, hence video authenticated

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53 Storage requirements Signature = Two 160 bit numbers = 320 bits After encryption 1024 bits Hash of every picture = 160 bits After encryption = 1024 bits If there are ‘n’ pictures in a video sequence Bits required for hash = 1024 * n Total bits required = 1024 * (n+1) If there are ‘x’ coded video sequences Total bits required = x * 1024 * (n+1)

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54 Conclusions Robust to temporal and spatial manipulations Can detect sender forgery Identifies tamper locations Not robust to quantization Neglect of chrominance coefficients may lead to attack on chroma components

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55 Future Work Include chrominance components Requires further research for robustness to quantization Watermarking the authentication data directly into the video may result in bit savings

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56 References 1)Atrey, P.K. et al “A hierarchical signature scheme for robust video authentication using secret sharing”, In Proc of IEEE 10th International Multimedia Modelling Conference, pp , 5-7 Jan )Der-Chyuan Lou and Jiang-Lung Liu, “Fault resilient and compression tolerant digital signature for image authentication”, IEEE Trans. on Consumer Electronics, Vol. 46, pp , Feb )Grosbois, R. and Ebrahimi, T., “Secure JPEG 2000-JPSEC”, In Proc of IEEE International Conference on Acoustics, Speech and Signal Processing, Vol. 4 pp , 6-10 Apr 2003.

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57 References (contd.) 4)Zhu, B.B., Swanson, M.D., and Tewfik, A.H. "When seeing isn't believing [multimedia authentication technologies]", IEEE Signal Processing Magazine, Vol.21, pp , Mar )Digital Signature Standard Federal Information Processing Standards Publication )Special Issue on H.264/AVC IEEE Trans. on Circuits and Systems for Video Technology, vol. 13, pp , Jul 2003.

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58 References (contd.) 7)Tamhankar, A. and Rao, K.R. “An overview of H.264/MPEG4- Part 10”, Video/Image Processing and Multimedia Communications, 4th EURASIP, Zagreb, Croatia, )H.264/AVC International Standard ITU ‑ T Rec. H.264 | ISO/IEC ‑ 10 version 3 9) H.264 Reference software 10) YUV 4:2:0 video sequences

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