Biblio

One of the fundamental methods for eavesdroppers to achieve a plaintext from a cryptogram is the brute force attack where possible candidates of decryption keys are exhaustively applied to the decryption algorithm. Here the only reason why the eavesdroppers believe to find the common-key and to achieve the plaintext is that the output of the decryption algorithm is contextually acceptable. According to this fact, this paper proposes a novel common-key cryptosystem where fake plaintexts which are also contextually acceptable are mixed into a cryptogram with the legal plaintext. If an eavesdropper applies a fake common-key to the decryption algorithm, it outputs the fake plaintexts which the eavesdroppers might believe legal. This paper also proposes concrete encryption/decryption algorithm which can be combined with any conventional common-key cryptosystem. Results of simulation experiments show the proposed method reduces probability for eavesdroppers to get legal plaintexts.

Ciphertext policy attribute-based encryption (CP-ABE) is a promising technology that offers fine-grained access control over encrypted data. In a CP-ABE scheme, any user can decrypt the ciphertext using his secret key if his attributes satisfy the access policy embedded in the ciphertext. Since the same ciphertext can be decrypted by multiple users with their own keys, the malicious users may intentionally leak their decryption keys for financial profits. So how to trace the malicious users becomes an important issue in a CP-ABE scheme. In addition, from the practical point of view, users may leave the system due to resignation or dismissal. So user revocation is another hot issue that should be solved. In this paper, we propose a practical CP-ABE scheme. On the one hand, our scheme has the properties of traceability and large universe. On the other hand, our scheme can solve the dynamic issue of user revocation. The proposed scheme is proved selectively secure in the standard model.

Data outsourcing in cloud is emerging as a successful paradigm that benefits organizations and enterprises with high-performance, low-cost, scalable data storage and sharing services. However, this paradigm also brings forth new challenges for data confidentiality because the outsourced are not under the physic control of the data owners. The existing schemes to achieve the security and usability goal usually apply encryption to the data before outsourcing them to the storage service providers (SSP), and disclose the decryption keys only to authorized user. They cannot ensure the security of data while operating data in cloud where the third-party services are usually semi-trustworthy, and need lots of time to deal with the data. We construct a privacy data management system appending hierarchical access control called HAC-DMS, which can not only assure security but also save plenty of time when updating data in cloud.

Data confidentiality can be effectively preserved through encryption. In certain situations, this is inadequate, as users may be coerced into disclosing their decryption keys. Steganographic techniques and deniable encryption algorithms have been devised to hide the very existence of encrypted data. We examine the feasibility and efficacy of deniable encryption for mobile devices. To address obstacles that can compromise plausibly deniable encryption (PDE) in a mobile environment, we design a system called Mobiflage. Mobiflage enables PDE on mobile devices by hiding encrypted volumes within random data in a devices free storage space. We leverage lessons learned from deniable encryption in the desktop environment, and design new countermeasures for threats specific to mobile systems. We provide two implementations for the Android OS, to assess the feasibility and performance of Mobiflage on different hardware profiles. MF-SD is designed for use on devices with FAT32 removable SD cards. Our MF-MTP variant supports devices that instead share a single internal partition for both apps and user accessible data. MF-MTP leverages certain Ext4 file system mechanisms and uses an adjusted data-block allocator. These new techniques for soring hidden volumes in Ext4 file systems can also be applied to other file systems to enable deniable encryption for desktop OSes and other mobile platforms.