An encryption scheme called the Randomized Dictionary Table (RDT), which embeds encryption into the LZ78 data compression method, is proposed and analyzed in this research. The basic idea is to construct multiple dictionaries with a different entry order and then randomly select one dictionary in each compression step according to a pseudo-random sequence. Our scheme incurs light computation overhead to encrypt the compressed data and does not impair the LZ compression ratio. Security analysis demonstrates that the proposed RDT scheme achieves high security strength under both the ciphertext only attack and the known/chosen plaintext attack.
A new paradigm of one-way hash function, called the distance-preserving hash function (DP hash function), is proposed and a soft multimedia content authentication scheme is developed accordingly in this work. The DP hash function has a distinct characteristic from regular hash functions. That is, when it is equipped with a correct key, the difference between two outputs reflects the distance between the corresponding inputs. However, if a wrong key value is used, the DP hash function reduces to a regular one-way hash function. We examine the theoretical aspect of the DP hash function and propose a practical way for its construction. The DP hash value of the multimedia feature vector is used as the authenticator for the corresponding content. By comparing the DP hash of received data and the received DP hash (authenticator), users can obtain the error between the received data and the original data. This error information indicates a degree of authenticity and allows users to render a soft decision rather than an "authentic or non-authentic" hard decision. Such a soft decision is helpful in applications where a small amount of distortion in the target data is acceptable, such as digital audio and video.
Efficient multimedia encryption algorithms are fundamental to multimedia data security because of the massive data size and the need of real-time processing. In this research, we present an efficient encryption scheme, called the RCI-QM coder, which achieves the objective of encryption with a regular QM coder by applying different coding conventions to encode individual symbols according to a statistically random sequence. One main advantage of our scheme is the negligible computation cost associated with encryption. We also demonstrate with cryptanalysis that the security level of our scheme is high enough to thwart most common attacks. The proposed RCI-QM coder is easy to implement in both software and hardware, while providing backward compatibility to the standard QM coder.
Efficient multimedia encryption algorithms play a key role in multimedia security protection. One multimedia encryption algorithm known as the MHT (Multiple Huffman Tables) method was recently developed by Wu and Kuo. Even though MHT has many desirable properties, it is vulnerable to the chosen-plaintext attack (CPA). An enhanced MHT algorithm is proposed in this work to overcome this drawback. It is proved mathematically that the proposed algorithm is secure against the chosen plaintext attack.