Ciphertext Policy Attribute-Based Encryption (CP-ABE) enforces expressive data access policies and each policy consists of a number of attributes. Most existing CP-ABE schemes incur a very large ciphertext size, which increases linearly with respect to the number of attributes in the access policy. Recently, Herranzproposed a construction of CP-ABE with constant ciphertext. However, Herranzdo not consider the recipients’ anonymity and the access policies are exposed to potential malicious attackers. On the other hand, existing privacy preserving schemes protect the anonymity but require bulky, linearly increasing ciphertext size. In this paper, we proposed a new construction of CP-ABE, named Privacy Preserving Constant CP-ABE (denoted as PP-CP-ABE) that significantly reduces the ciphertext to a constant size with any given number of attributes. Furthermore, PP-CP-ABE leverages a hidden policy construction such that the recipients’ privacy is preserved efficiently. As far as we know, PP-CP-ABE is the first construction with such properties. Furthermore, we developed a Privacy Preserving Attribute-Based Broadcast Encryption (PP-AB-BE) scheme. Compared to existing Broadcast Encryption (BE) schemes, PP-AB-BE is more flexible because a broadcasted message can be encrypted by an expressive hidden access policy, either with or without explicit specifying the receivers. Moreover, PP-AB-BE significantly reduces the storage and communication overhead to the order of${\mbi {O}}(\log {\mbi {N}})$, where${\mbi {N}}$is the system size. Also, we proved, using information theoretical approaches, PP-AB-BE attains minimal bound on storage overhead for each user to cover all possible subgroups in the communication system.

We propose a vehicular network trust model that integrates cryptography-based entity trust and email-based social trust. The entity trust provides security protections such as origin integrity, data integrity, and confidentiality. The social trust provides a level of belief on the data transmitted by an entity. To achieve the email-based social trust, we require each user to run an automated agent that performs trust evaluation checks and processes trust checking requests. The requests are from their highly trusted contacts or through a trusted proxy server maintained by the email service provider. We utilize identity-based cryptography (IBC) to integrate entity trust and social trust. This allows us to use a unique identity (e.g., an email address) for each entity. Further, we use the IBC based attribute based cryptography to develop secure group communications in vehicular networks. Finally, we present research challenges and potential research directions to extend this work.

Existing CP-ABE schemes incur very large ciphertext size, which increases linearly with respect to the number of attributes in the access policy. Large ciphertext prevents CP-ABE from being adopted in the communication constrained environments. In this paper, we proposed a new construction of CP-ABE, named Constant-size CP-ABE (denoted as CCP-ABE) that significantly reduces the ciphertext to a constant size for an AND gate access policy with any given number of attributes. Each ciphertext in CCP-ABE requires only elements on a bilinear group.

Many IP multicast-based applications, such as multimedia conferencing, multiplayer games, require controlling the group memberships of senders and receivers. One common solution is to encrypt the data with a session key shared with all authorized senders/receivers. To efficiently update the session key in the event of member removal, many rooted-tree based group key distribution schemes have been proposed. However, most of the existing rooted-tree based schemes are not optimal. In other words, given the O(log N) storage overhead, the communication overhead is not minimized. On the other hand, although Flat Table scheme achieves optimality, it is rather dismissed due to the vulnerability to collusion attacks. In this paper, we propose a key distribution scheme - EGK that attains the same optimality as Flat Table without collusion vulnerability. Additionally, EGK provides constant message size and requires O(log N) storage overhead at the group controller, which makes EGK suitable for applications containing a large number of multicasting group members. Moreover, adding members in EGK requires just one multicasting message. EGK is the first work with such features and out- performs all existing schemes.

Extremely limited in computational and energy capability, RFID tags, especially passive tags, can hardly authenticate the scanning readers. Thus, information leakage for RFID tags is one of the most challenging open problems holding back users' confidence in adopting RFID technologies. To solve this problem, we propose Smart RFID Keeper (SRK) - a distributed, off-tag RFID data access control Mechanism, which is installed in RFID enabled environments to regulate RFID scanning. To solve the information leakage threat, SRK is designed to (1) authenticate the user; (2) detect and counter unauthorized accesses to RFID tags and (3) enforce fine grained access policy.

Access control for RFID tags is challenging due to the limited computational and energy capability of RFID tags. To solve this problem, we propose RFID Keeper - an RFID data access control mechanism based on RFID media access control protocols. RFID Keeper is designed to detect and counter unauthorized accesses to RFID tags.