Cloud Data Auditing Using Proofs of Retrievability

Cloud servers offer data outsourcing facility to their clients. A client outsources her data without having any copy at her end. Therefore, she needs a guarantee that her data are not modified by the server which may be malicious. Data auditing is performed on the outsourced data to resolve this issue. Moreover, the client may want all her data to be stored untampered. In this chapter, we describe proofs of retrievability (POR) that convince the client about the integrity of all her data.Comment: A version has been published as a book chapter in Guide to Security Assurance for Cloud Computing (Springer International Publishing Switzerland 2015

Group Selection and Key Management Strategies for Ciphertext-Policy Attribute-Based Encryption

Ciphertext-Policy Attribute-Based Encryption (CPABE) was introduced by Bethencourt, Sahai, and Waters, as an improvement of Identity Based Encryption, allowing fine grained control of access to encrypted files by restricting access to only users whose attributes match that of the monotonic access tree of the encrypted file. Through these modifications, encrypted files can be placed securely on an unsecure server, without fear of malicious users being able to access the files, while allowing each user to have a unique key, reducing the vulnerabilites associated with sharing a key between multiple users. However, due to the fact that CPABE was designed for the purpose of not using trusted servers, key management strategies such as efficient renewal and immediate key revocation are inherently prevented. In turn, this reduces security of the entire scheme, as a user could maliciously keep a key after having an attribute changed or revoked, using the old key to decrypt files that they should not have access to with their new key. Additionally, the original CPABE implementation provided does not discuss the selection of the underlying bilinear pairing which is used as the cryptographic primitive for the scheme. This thesis explores different possibilites for improvement to CPABE, in both the choice of bilinear group used, as well as support for key management that does not rely on proxy servers while minimizing the communication overhead. Through this work, it was found that nonsupersingular elliptic curves can be used for CPABE, and Barreto-Naehrig curves allowed the fastest encryption and key generation in CHARM, but were the slowest curves for decryption due to the large size of the output group. Key management was performed by using a key-insulation method, which provided helper keys which allow keys to be transformed over different time periods, with revocation and renewal through key update. Unfortunately, this does not allow immediate revocation, and revoked keys are still valid until the end of the time period during which they are revoked. Discussion of other key management methods is presented to show that immediate key revocation is difficult without using trusted servers to control access

Novel Techniques for Secure Use of Public Cloud Computing Resources

The federal government has an expressed interest in moving data and services to third party service providers in order to take advantage of the flexibility, scalability, and potential cost savings. This approach is called cloud computing. The thesis for this research is that efficient techniques exist to support the secure use of public cloud computing resources by a large, federated enterprise. The primary contributions of this research are the novel cryptographic system MA-AHASBE (Multi-Authority Anonymous Hierarchical Attribute-Set Based Encryption), and the techniques used to incorporate MA-AHASBE in a real world application. Performance results indicate that while there is a cost associated with enforcing the suggested security model, the cost is not unreasonable and the benefits in security can be significant. The contributions of this research give the DoD additional tools for supporting the mission while taking advantage of the cost efficient public cloud computing resources that are becoming widely available

Pairing-based cryptosystems and key agreement protocols.

For a long time, pairings on elliptic curves have been considered to be destructive in elliptic curve cryptography. Only recently after some pioneering works, particularly the well-known Boneh-Franklin identity-based encryption (IBE), pairings have quickly become an important tool to construct novel cryptographic schemes. In this thesis, several new cryptographic schemes with pairings are proposed, which are both efficient and secure with respect to a properly defined security model, and some relevant previous schemes are revisited. IBE provides a public key encryption mechanism where a public key can be an arbitrary string such as an entity identifier and unwieldy certificates are unnecessary. Based on the Sakai-Kasahara key construction, an IBE scheme which is secure in the Boneh-Franklin IBE model is constructed, and two identity-based key encapsulation mechanisms are proposed. These schemes achieve the best efficiency among the existing schemes to date. Recently Al-Riyami and Paterson introduced the certificateless public key encryption (CL-PKE) paradigm, which eliminates the need of certificates and at the same time retains the desirable properties of IBE without the key escrow problem. The security formulation of CL-PKE is revisited and a strong security model for this type of mechanism is defined. Following a heuristic approach, three efficient CL-PKE schemes which are secure in the defined strong security model are proposed. Identity-based two-party key agreement protocols from pairings are also investigated. The Bellare-Rogaway key agreement model is enhanced and within the model several previously unproven protocols in the literature are formally analysed. In considering that the user identity may be sensitive information in many environments, an identity-based key agreement protocol with unilateral identity privacy is proposed

BINARY EDWARDS CURVES IN ELLIPTIC CURVE CRYPTOGRAPHY

Edwards curves are a new normal form for elliptic curves that exhibit some cryp- tographically desirable properties and advantages over the typical Weierstrass form. Because the group law on an Edwards curve (normal, twisted, or binary) is complete and unified, implementations can be safer from side channel or exceptional procedure attacks. The different types of Edwards provide a better platform for cryptographic primitives, since they have more security built into them from the mathematic foun- dation up. Of the three types of Edwards curves—original, twisted, and binary—there hasn’t been as much work done on binary curves. We provide the necessary motivation and background, and then delve into the theory of binary Edwards curves. Next, we examine practical considerations that separate binary Edwards curves from other recently proposed normal forms. After that, we provide some of the theory for bi- nary curves that has been worked on for other types already: pairing computations. We next explore some applications of elliptic curve and pairing-based cryptography wherein the added security of binary Edwards curves may come in handy. Finally, we finish with a discussion of e2c2, a modern C++11 library we’ve developed for Edwards Elliptic Curve Cryptography