Least-Significant-Digit Steganography in Low Bitrate Speech
For steganography over speech frames, Least Significant-Bit (LSB) approach has been one of the most important alternatives. However, its embedded capacity is quite limited, due to the low redundancy characteristic of low bit-rate speech. Thus, the authors suggest a novel Least Significant Digit (LSD) method in this paper, which makes full use of the frame bits to hide secret messages and provides a larger embedding capacity than the LSB method. The LSD method exploits the multiple adjacent states of frame parameters, which are produced by multiple modifications (e.g. +1, ??'1,+2, ??'2) and encoded as LSDs using a multi-ary numeration system. Beyond providing a considerable embedding capacity, the LSD method further extends the key space for key-based steganography, which can enhance the security of covert communication.