DIGITAL SIGNATURE(DS) IN VIDEO

Contents  What is Digital Signature(DS)?  General Signature Vs. Digital Signatures  How DS is Different from Encryption?  Working of DS  Video Authentication of H.264 using DS  Question-Answer  References

What is Digital Signature?  A digital signature is a mathematical scheme for demonstrating the authenticity of a digital message, document, digital image or digital video.  A valid digital signature gives a recipient reason to believe that the message was created by a known sender.  Digital signature provide authenticity, integrity and nonrepudiation.  The sender cannot deny that we have not have not sent the message (Nonrepudiation).  Message is not modified indicate message Integrity.

General Signature Vs. Digital signature-  General signature is part of documents but digital signature is not part of documents, it is sending with documents.  For verification of general signature in documents we compare it with the original signature of file.  But In digital signature verification we compute digital signature at receiver site.  If computed digital signature matched with sender side DS then documents is authentic otherwise tampered.

Continue………  In general signature we use one signature in many documents(One to Many) but in digital signature we use one digital signature for one document (One to One).  Digital signature is more robust in comparison to General Signature.  Digital signature is complex but general signature is simple.  Copying of General signature is easy but not for DS.

Digital signature Process-  The sender uses a signing algorithm to sign the message.  The message and the signature are sent to the receiver.  The receiver receives the message and the signature and applies the verifying algorithm to the combination  If the result is true, the message is accepted; otherwise, it is rejected.

Digital Signature Process-

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How DS is Different from Encryption? 9  Digital Signature(DS)- 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

Encryption………. 10 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

Continue……….  DS require public key cryptography system, sender sign with its own private key and receiver verify it with public key provide by sender.  Digital Signature use private and public key of sender and public key of cryptography use private and public key of receiver.  Digital signature provide message authentication, Integrity and nonrepudiation but not privacy.

Working of DS-

Video Authentication Scheme for H.264

Encoder-  Encoder for video- 14  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

Encoder (contd.)  Intra 16x16 MB 15 T Q T 4X4 integer DCT 4X4 Hadamard transform Original 16x16 MB residual Transformed 16x16 MB Quantized Hadamard coefficients Q Feature data

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 16

Encoder (contd.)  Signature generation for a coded video sequence 17 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 H D E

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 18

Decoder-  Loam values only  Features taken in transform domain  Signature verification for every coded video sequence 19

Decoder (contd.)  Intra 4x4 and Inter MB’s 20 DCAC (0,0) (3,0) (0,3) (3,3) 4x4 block of transform coefficients before inverse quantization Feature data

Decoder (contd.)  Intra 16x16 MB 21 Transformed 16x16 MB before inverse quantization Hadamard coefficients before inverse quantization 15 AC coefficients Feature data

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 22

Decoder (contd.)  Signature verification for a coded video sequence 23 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

Conclusion of Decoder-  Tampering frames indicate the Signature failure  Sender forgery indicate the Signature failure  If we can not find out out the reason of signature failure and location of tampering then.  Adjust the encoder to accommodate these issues. 24

References: DigitalSignature13.ppt