7 Multimedia Authentication and Watermarking

Most multimedia signals today are in digital formats which are easy to reproduce and modify without any trace of manipulations. In this chapter, we present a comprehensive review of current technologies for multimedia data authentication and tamper detection. We first introduce in Section 7.2 the problem issues and general requirements for a multimedia authentication system. This is followed in Section 7.3 with detailed descriptions of the current algorithms for the three types of multimedia authentication: hard or complete authentication, soft authentication, and content-based authentication. The conclusion and future research directions are presented in Section 7.4. 7.1 Introduction Nowadays the vast majority of multimedia signals are in digital formats which offer significant advantages over analog formats in terms of quality and efficiency in creation, storage and distribution. They can also be easily edited without obvious trace of manipulations with modern PC and software. In today's digital world seeing is no longer believing! People seek for information with integrity and authenticity. This makes detection of illegal manipulations an important issue for digital multimedia. Authentication technologies fulfill an increasing need for trustworthy digital data in commerce, industry, defense, etc. General data authentication has been well studied in cryptography. The classical scenario for an authentication problem can be described as follows: A sender S sends a digital message M to a receiver R. An effective authentication system must ensure that the message M received by R: (1) is exactly the same as that sent by S (integrity verification); (2) is really sent by S (origination verification); and (3) S cannot deny having sent M (non-repudiation). Two types of authentication techniques have been developed in cryptography: digital signature and message authentication codes (MACs) [1, 2]. The digital signature approach applies a cryptographic hash function to the message M. The hash value is then encrypted with the sender S's private key. The result is the digital signature of the message M. The digital signature is sent to R together with the message M it authenticates. The receiver R uses the sender's public key to decrypt the digital signature to obtain the original hash value, which is compared with the hash value calculated from the received message M. If they are the same, then the message R