Cloud storage is an increasingly popular application of cloud computing, which can provide on-demand outsourcing data services for both organizations and individuals. However, users may not fully trust the cloud service providers (CSPs) in that it is difficult to determine whether the CSPs meet their legal expectations for data security. Therefore, it is critical to develop efficient auditing techniques to strengthen data owners' trust and confidence in cloud storage. In this paper, we present a novel public auditing scheme for secure cloud storage based on dynamic hash table (DHT), which is a new two-dimensional data structure located at a third parity auditor (TPA) to record the data property information for dynamic auditing. Differing from the existing works, the proposed scheme migrates the authorized information from the CSP to the TPA, and thereby significantly reduces the computational cost and communication overhead. Meanwhile, exploiting the structural advantages of the DHT, our scheme can also achieve higher updating efficiency than the state-of-the-art schemes. In addition, we extend our scheme to support privacy preservation by combining the homomorphic authenticator based on the public key with the random masking generated by the TPA, and achieve batch auditing by employing the aggregate BLS signature technique. We formally prove the security of the proposed scheme, and evaluate the auditing performance by detailed experiments and comparisons with the existing ones. The results demonstrate that the proposed scheme can effectively achieve secure auditing for cloud storage, and outperforms the previous schemes in computation complexity, storage costs and communication overhead.

Abstract Steganography in low bit‐rate speech streams is an important branch of Voice‐over‐Internet Protocol steganography. From the point of preventing cybercrimes, it is significant to design effective steganalysis methods. In this paper, we present a support‐vector‐machine‐based steganalysis of low bit‐rate speech exploiting statistic characteristics of pulse positions. Specifically, we utilize the probability distribution of pulse positions as a long‐time distribution feature, extract Markov transition probabilities of pulse positions according to the short‐time invariance characteristic of speech signals, and employ joint probability matrices to characterize the pulse‐to‐pulse correlation. We evaluate the performance of the proposed method with a large number of G.729a‐encoded speech samples and compare it with the state‐of‐the‐art methods. The experimental results demonstrate that our method significantly outperforms the previous ones on detection accuracy, false positive rate, and false negative rate at any given embedding rates or with any sample lengths. Particularly, this method can successfully detect steganography employing only one or a few of the potential cover bits, which is hard to be effectively detected by the existing methods. Copyright © 2016 John Wiley & Sons, Ltd.

Steganography in low bit-rare speech streams is an important branch of Voice-over-IP steganography. From the point of preventing cybercrimes, it is significant to design effective steganalysis methods. In this paper, we present a support-vector-machine based steganalysis of low bit-rate speech exploiting statistic characteristics of pulse positions. Specifically, we utilize the probability distribution of pulse positions as a long-time distribution feature, extract Markov transition probabilities of pulse positions according to the short-time invariance characteristic of speech signals, and employ joint probability matrices to characterize the pulse-to-pulse correlation. We evaluate the performance of the proposed method with a large number of G.729a encoded samples, and compare it with the state-of-the-art methods. The experimental results demonstrate that our method significantly outperforms the previous ones on detection accuracy at any given embedding rates or with any sample lengths. Particularly, this method can successfully detect steganography employing only one or a few of the potential cover bits, which is hard to be effectively detected by the existing methods.

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 bitrate speech. Thus, we 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. The LSD method is implemented and evaluated with G.723.1 as the codec for speeches. The experiment results show that, compared with the previous LSB method, the LSD method increases around 30% of embedding capacity, and induces less distortion given the same embedding capacity.

Common least significant bit (LSB) relevant steganography methods in speech frames often base on bits evaluation by certain speech quality evaluation criterion and together with some coding and embedding strategies to enhance imperceptibility and efficiency. However, some embedding capabilities and security strategy are neglected. This paper proposes a state-based steganography method which fully investigates speech frame features in order to expand embedding capabilities and enhance steganography security. In the proposed method, embedding capabilities are measured by available numbers of states relative to current frame parameters rather than information bits. And secret information embedding procedure is performed by the chosen states mapped operations. This is a basic fine-grained steganography solution which is useful for other algorithms based on it. The experimental results have demonstrated that statebased method outperforms traditional LSB substitution in overall performance and introduces limited latency, which meets the realtime requirement in covert communications.

Differing from applying steganography on storage cover media, steganography on voice over IP (VoIP) must often delicately balance between providing adequate security and maintaining low latency for real-time services. This paper presents a novel real-time steganography model for VoIP that aims at providing good security for secret messages without sacrificing real-time performance. We achieve this goal by employing the well-known least-significant-bits (LSB) substitution approach to provide a reasonable tradeoff between the adequate information hiding requirement (good security and sufficient capacity) and the low latency requirement for VoIP. Further, we incorporate the M-sequence technique to eliminate the correlation among secret messages to resist the statistical detection based on the fact that the distribution of the LSBs in the stego-speech is not uniform and to provide a short-term security protection of secret messages. To accurately recover secret messages at the receiver side, we design a synchronization mechanism based on the RSA key agreement and the synchronized sequence transmission using techniques of the protocol steganography, which can effectively enhance the flexibility of the covert communication system and be extended to other steganography schemes based on real-time systems. We evaluate the effectiveness of our model with ITU-T G.729a as the codec of the cover speech in StegTalk, a covert communication system based on VoIP. The experimental results demonstrate that our technique provides good security and transparency for transmitting secret messages while adequately meeting the real-time requirement of VoIP.

This paper presents an adaptive steganography scheme for Voice over IP (VoIP). Differing from existing steganography techniques for VoIP, this scheme enhances the embedding transparency by taking into account the similarity between least significant bits (LSBs) and embedded messages. Moreover, we introduce the notion of partial similarity value (PSV). By properly setting the threshold PSV, we can adaptively balance the embedding transparency and capacity. We evaluate the effectiveness of this scheme with G.729a as the codec of the cover speech in StegTalk, a covert communication system based on VoIP. The experimental results demonstrate that our technique provides better performance than the traditional method.