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A new method to encrypt a compressed multimedia bit stream, which is the output of any compression system using an entropy coder in the last stage, is proposed in this research. The basic idea is to partition a coded bit stream into random-sized blocks and perform a random rotation in each block. The proposed encryption scheme demands low computational overhead and does not increase the size of compressed bit stream. Security analysis to both the ciphertext-only attack and the known/chosen-plaintext attack shows that the proposed algorithm achieves high security.

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.

Efficient multimedia encryption algorithms play a key role in multimedia security protection. One algorithm known as the MHT (multiple Huffman tables) method was recently developed by Wu and Kuo (2001; 2000). Although MHT has many desirable advantages, it is vulnerable under the chosen-plaintext attack (CPA). In this work, an enhanced MHT encryption scheme is proposed to remedy this drawback using the idea of key hopping. It is demonstrated by mathematical analysis that our proposed scheme is secure against chosen plaintext attack.

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 in [4] and [5]. 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.

This work investigates the problem of efficient multimedia data encryption. A novel methodology is proposed to achieve encryption by controlling certain operations in the data compression process using a secret key. The new encryption approach consists of two cascaded modules. The first one is called randomized entropy coding (REC) while the second one is called rotation in partitioned bitstream (RPB). By leveraging the structure of the entropy coder, the joint REC/RPB encryption scheme incurs extremely low computational and implementation costs. Security analysis shows that the proposed scheme can withstand the ciphertext-only attack as well as the known/chosen plaintext attack. The efficiency and security of the proposed encryption scheme makes it an ideal choice in secure media applications where a large amount of multimedia data has to be encrypted/decrypted in real time.