In this paper, we revisit the problem of finding the longest systematic-length k for a linear minimum storage regenerating (MSR) code with optimal repair of only systematic part, for a given per-node storage capacity l and an arbitrary number of parity nodes r. We study the problem by following a geometric analysis of linear subspaces and operators. First, a simple quadratic bound is given, which implies that k = r + 2 is the largest number of systematic nodes in the scalar scenario. Second, an r-based-log bound is derived, which is superior to the upper bound on log-base 2 in the prior work. Finally, an explicit upper bound depending on the value of r2/l is introduced, which further extends the corresponding result in the literature.

In this paper, we revisit the problem of characterizing the secrecy capacity of minimum storage regenerating (MSR) codes under the passive (l1, l2)-eavesdropper model, where the eavesdropper has access to data stored on l1nodes and the repair data for an additional l2nodes. We study it from the informationtheoretic perspective. First, some general properties of MSR codes as well as a simple and generally applicable upper bound on secrecy capacity are given. Second, a new concept of stable MSR codes is introduced, where the stable property is shown to be closely linked with secrecy capacity. Finally, a comprehensive and explicit result on secrecy capacity in the linear MSR scenario is present, which generalizes all related works in the literature and also predicts certain results for some unexplored linear MSR codes.

Cloud computing is a promising computing paradigm which has drawn extensive attention. Serious concerns over the reliability and confidentiality of the outsourced data are arising. Traditional encryption methods can, guarantee data confidentiality, however, it also limits the cloud's functionality as few operations are supported over encrypted data. In this study, the authors construct an enhanced cloud that not only provides secure and robust data storage, but also supports the functionality that the cipher data can be forwarded without being retrieved back. Specifically, they design an all‐or‐nothing‐transform‐based encryption and a variant of ElGamal‐based proxy re‐encryption algorithms, blending them with Reed–Solomon code, the authors’ scheme is quite more efficient compared with previous studies because it only needs to update partial data blocks instead of the whole file for data forwarding. Besides, the authors’ scheme also satisfies another practical property that the original data owner can no longer decrypt or forward the re‐encrypted data to others after a complete forwarding instance, which is termed to be ‘original inaccessibility’ in this study. Analysis shows that the authors’ scheme is secure and satisfactory. Finally, the authors theoretically and experimentally evaluate its performance and the results indicate that their scheme is efficient during file dispersal, forward and retrieval.

Here, we revisit the problem of exploring the secrecy capacity of minimum storage cooperative regenerating (MSCR) codes under the (l2 l2)-eavesdropper model, where the eavesdropper can observe the data stored on l1nodes and the repair downloads of an additional l2nodes. Compared to minimum storage regenerating (MSR) codes which support only single node repairs, MSCR codes allow efficient simultaneous repairs of multiple failed nodes, referred to as a repair group. However, the repair data sent from a helper node to another failed node may vary with different repair groups or the sets of helper nodes, which would inevitably leak more data information to the eavesdropper and even render the storage system unable to maintain any data secrecy. In this paper, we introduce and study a special category of MSCR codes, termed “stable” MSCR codes, where the repair data from any one helper node to any one failed node is required to be independent of the repair group or the set of helper nodes. Our main contributions include: 1) Demonstrating that two existing MSCR codes inherently are not stable and thus have poor secrecy capacity; 2) Converting one existing MSCR code to a stable one, which offers better secrecy capacity when compared to the original one; and 3) Employing information theoretic analysis to characterize the secrecy capacity of stable MSCR codes in certain situations.

Cloud computing has been envisioned as the next generation architecture of the IT enterprise, but there exist many security problems. A significant problem encountered in the context of cloud storage is whether there exists some potential vulnerabilities towards cloud storage system after introducing third parties. Public verification enables a third party auditor (TPA), on behalf of users who lack the resources and expertise, to verify the integrity of the stored data. Many existing auditing schemes always assume TPA is reliable and independent. This work studies the problem what if certain TPAs are semi‐trusted or even potentially malicious in some situations. Actually, the authors consider the task of allowing such a TPA to involve in the audit scheme. They propose a feedback‐based audit scheme via which users are relaxed from interacting with cloud service provider (CSP) and can check the integrity of stored data by themselves instead of TPA yet. Specifically, TPA generates the feedback through processing the proof from CSP and returns it to user which is yet unforgeable to TPA and checked exclusively by user. Through detailed security and performance analysis, the author's scheme is shown to be more secure and lightweight.