Abstract
Cryptography is an inherently interdisciplinary area and the development of high-quality cryptographic software is a time-consuming task drawing on skills from mathematics, computer science and electrical engineering, only achievable by highly skilled programmers. The challenge is to map high-level cryptographic specifications phrased using mathematical abstractions into efficient implementations at the level of C or assembly that can be deployed on a target computational platform, whilst adhering to the specification both in terms of correctness and security. The High Assurance Software Laboratory at INESC-TEC maintains a domain-specific toolchain for the specification, implementation and verification of cryptographic software centred on CAO, a cryptography analyses and operations-aware language.

Abstract
Exciting new capabilities of modern trusted hardware technologies allow for the execution of arbitrary code within environments completely isolated from the rest of the system and provide cryptographic mechanisms for securely reporting on these executions to remote parties. Rigorously proving security of protocols that rely on this type of hardware faces two obstacles. The first is to develop models appropriate for the induced trust assumptions (e.g., what is the correct notion of a party when the peer one wishes to communicate with is a specific instance of an an outsourced program). The second is to develop scalable analysis methods, as the inherent stateful nature of the platforms precludes the application of existing modular analysis techniques that require high degrees of independence between the components. We give the first steps in this direction by studying three cryptographic tools which have been commonly associated with this new generation of trusted hardware solutions. Specifically, we provide formal security definitions, generic constructions and security analysis for attested computation, key-exchange for attestation and secure outsourced computation. Our approach is incremental: each of the concepts relies on the previous ones according to an approach that is quasi-modular. For example we show how to build a secure outsourced computation scheme from an arbitrary attestation protocol combined together with a key-exchange and an encryption scheme.

Abstract

Abstract
We provide further evidence that implementing software countermeasures against timing attacks is a non-trivial task and requires domain-specific software development processes: we report an implementation bug in the s2n library, recently released by AWS Labs. This bug ( now fixed) allowed bypassing the balancing countermeasures against timing attacks deployed in the implementation of the MAC-then-Encode-then-CBC-Encrypt (MEE-CBC) component, creating a timing side-channel similar to that exploited by Lucky 13. Although such an attack could only be launched when the MEE-CBC component is used in isolation - Albrecht and Paterson recently confirmed in independent work that s2n's second line of defence, once reinforced, provides adequate mitigation against current adversary capabilities - its existence serves as further evidence to the fact that conventional software validation processes are not effective in the study and validation of security properties. To solve this problem, we define a methodology for proving security of implementations in the presence of timing attackers: first, prove black-box security of an algorithmic description of a cryptographic construction; then, establish functional correctness of an implementation with respect to the algorithmic description; and finally, prove that the implementation is leakage secure. We present a proof-of-concept application of our methodology to MEE-CBC, bringing together three different formal verification tools to produce an assembly implementation of this construction that is verifiably secure against adversaries with access to some timing leakage. Our methodology subsumes previous work connecting provable security and side-channel analysis at the implementation level, and supports the verification of a much larger case study. Our case study itself provides the first provable security validation of complex timing countermeasures deployed, for example, in OpenSSL.

Abstract
CAO is a domain-specific imperative language for cryptography, offering a rich mathematical type system and crypto-oriented language constructions. We describe the design and implementation of a deductive verification platform for CAO and demonstrate that the development time of such a complex verification tool could be greatly reduced by building on the Jessie plug-in included in the Frama-C framework. We discuss the interesting challenges raised by the domain-specific characteristics of CAO, and describe how we tackle these problems in our design. We base our presentation on real-world examples of CAO code, extracted from the open-source code of the NaCl cryptographic library, and illustrate how various cryptography-relevant security properties can be verified.

Abstract
Formal verification of cryptographic software implementations poses significant challenges for off-the-shelf tools. This is due to the domain-specific characteristics of the code, involving aggressive optimizations and non-functional security requirements, namely the critical aspect of countermeasures against side-channel attacks. In this paper, we extend previous results supporting the practicality of self-composition proofs of non-interference and generalizations thereof. We tackle the formal verification of high-level security policies adopted in the implementation of the recently proposed NaCl cryptographic library. We formalize these policies and propose a formal verification approach based on self-composition, extending the range of security policies that could previously be handled using this technique. We demonstrate our results by addressing compliance with the NaCl security policies in real-world cryptographic code, highlighting the potential for automation of our techniques.