Abstract:
Due to the development of digital technologies, new social issues relating to malicious
attacks and unauthorized tampering to speech, such as content replacement and voice
morphing, have arisen. Using advanced speech analysis and synthesis tools enables the
speech to be tampered without leaving any perceptual clues. As an important information
carrier, the originality, integrity, and authenticity of speech signals should be strictly
confirmed.
Authentication and tampering detection of digital signals is one of the main
applications of digital watermarking. In this thesis, an efficient speech watermarking
method is proposed to generate self-embedding speech signals in that hash representation
of a speech signal, which is assumed as watermark, is embedded into the signal itself
without affecting the original quality. The proposed system is intended to satisfy blindness,
inaudibility, and fragility against malicious modifications.
The proposed watermarking method in this thesis is a kind of fragile watermarking
and thus the hash information (watermark) in the tampered regions is destroyed when
tampering occurs. This feature helps the receiver to detect and localize the tampering
regions by comparing the original hash information and the extracted hash from the
received speech. The perfect match of the hash information confirms the integrity and
originality of the received speech; otherwise it indicates tampering.
In this thesis, performance of the proposed system is tested on 40 read speech files
which are International news and Burmese news read by 20 female and 20 male
announcers. The proposed method is implemented in MATLAB and fragility against
malicious modification is evaluated by applying various kinds of tampering such as
compression, zeroing, adding noise, time scaling, and reverberation attacks on the
watermarked speech files. Experimental results show that the proposed method is relevant
with the main requirements of a good watermarking scheme: inaudibility and blindness in
addition to fragility. Therefore, the proposed system is really useful for applications of
criminal investigation and digital forensics where the integrity and originality of the speech
evidence is extremely important.
