We describe Charm, an extensible framework designed for rapid prototyping of cryptographic systems that utilize the latest advances in cryptography, such as identity and attribute-based encryption, as well as the traditional cryptographic functions. Charm is designed to minimize code complexity, promote code re-use, and to automate interoperability, while not compromising on efficiency.Charm was designed from the ground up to support the implementation of advanced cryptographic schemes. It includes support for multiple cryptographic settings, an extensive library of re-usable code, and a protocol engine to aid in the development of interactive protocols. Our framework also provides a series of specialized tools that enable different cryptosystems to interoperate.We implemented over twenty cryptographic schemes using Charm, including some new ones that to our knowledge have never been built in practice. This paper describes our modular architecture, which includes a built-in benchmarking module that we use to compare the performance of primitives written in Python to comparable C implementations. We show that in many cases our techniques result in a potential order of magnitude decrease in code size, while inducing an acceptable performance impact.

We provide a design and implementation of self-protecting electronic medical records (EMRs) using attribute-based encryption on mobile devices. Our system allows healthcare organizations to export EMRs to locations outside of their trust boundary. In contrast to previous approaches, our solution is designed to maintain EMR availability even when providers are o✏ine, i.e., where network connectivity is not available. To balance the needs of emergency care and patient privacy, our system is designed to provide fine-grained encryption and is able to protect individual items within an EMR, where each encrypted item may have its own access control policy. We implemented a prototype system using a new key-and ciphertext-policy attribute-based encryption library that we developed. Our implementation, which includes an iPhone app for storing and managing EMRs offline, allows for flexible and automated policy generation. An evaluation of our design shows that our ABE library performs well, has acceptable storage requirements, and is practical and usable on modern smartphones.

No abstract

Pairing-based cryptography has exploded over the last decade, as this algebraic setting offers good functionality and efficiency. However, there is a huge security gap between how schemes are usually analyzed in the academic literature and how they are typically implemented. The issue at play is that there exist multiple types of pairings: Type-I called "symmetric" is typically how schemes are presented and proven secure in the literature, because it is simpler and the complexity assumptions can be weaker; however, Type-III called "asymmetric" is typically the most efficient choice for an implementation in terms of bandwidth and computation time. There are two main complexities when moving from one pairing type to another. First, the change in algebraic setting invalidates the original security proof. Second, there are usually multiple (possibly thousands) of ways to translate from a Type-I to a Type-III scheme, and the "best" translation may depend on the application. Our contribution is the design, development and evaluation of a new software tool, Auto-Group+, that automatically translates from Type-I to Type-III pairings. The output of Au-toGroup+ is: (1) "secure" provided the input is "secure" and (2) optimal based on the user's efficiency constraints (excluding software and run-time errors). Prior automation work for pairings was either not guaranteed to be secure or only partially automated and impractically slow. This work addresses the pairing security gap by realizing a fast and secure translation tool.

As devices everywhere increasingly communicate with each other, many security applications will require low-bandwidth signatures that can be processed quickly. Pairing-based signatures can be very short, but are often costly to verify. Fortunately, they also tend to have efficient batch verification algorithms. Finding these batching algorithms by hand, however, can be tedious and error prone.We address this by presenting AutoBatch, an automated tool for generating batch verification code in either Python or C++ from a high level representation of a signature scheme. AutoBatch outputs both software and, for transparency, a LaTeX file describing the batching algorithm and arguing that it preserves the unforgeability of the original scheme.We tested AutoBatch on over a dozen pairing-based schemes to demonstrate that a computer could find competitive batching solutions in a reasonable amount of time. In particular, it found an algorithm that is faster than a batching algorithm from Eurocrypt 2010. Another novel contribution is that it handles cross-scheme batching, where it searches for a common algebraic structure between two distinct schemes and attempts to batch them together.In this work, we expand upon our paper on AutoBatch appearing in ACM CCS 2012 [2] in a number of ways. We add a new loop-unrolling technique and show that it helps cut the batch verification cost of one scheme by roughly half. We describe our pruning and search algorithms in greater detail, including pseudocode and diagrams. All experiments were also re-run using the RELIC pairing library. We compare those results to our earlier results using the MIRACL library, and discuss why RELIC outperforms MIRACL in all but two cases. Automated proofs of several new batching algorithms are also included.AutoBatch is a useful tool for cryptographic designers and implementors, and to our knowledge, it is the first attempt to outsource to machines the design, proof writing and implementation of signature batch verification schemes.