Multimedia Document Authentication using On-line Signatures as Watermarks

Authentication of digital documents is an important concern as digital documents are replacing the traditional paper-based documents for o#cial and legal purposes. This is especially true in the case of documents that are exchanged over the Internet, which could be accessed and modified by intruders. The most popular methods used for authentication of digital documents are public key encryption-based authentication and digital watermarking. Traditional watermarking techniques embed a pre-determined character string, such as the company logo, in a document. We propose a fragile watermarking system, which uses an on-line signature of the author as the watermark in a document. The embedding of a biometric characteristic such as signature in a document enables us to verify the identity of the author using a set of reference signatures, in addition to ascertaining the document integrity. The receiver of the document reconstructs the signature used to watermark the document, which is then used to verify the author's claimed identity. The paper presents a signature encoding scheme, which facilitates reconstruction by the receiver, while reducing the chances of collusion attacks