Certificateless cryptography inherits a solution to the certificate management problem in public-key encryption from identity-based techniques, whilst removing the secret key escrow functionality inherent to the identity-based setting. Signcryption schemes achieve confidentiality and authentication simultaneously by combining public-key encryption and digital signatures, offering better overall performance and security. In this paper, we introduce the notion of certificateless signcryption and present an efficient construction which guarantees security under insider attacks, and therefore provides forward secrecy and non-repudiation.

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.

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We present a high-assurance software stack for secure function evaluation (SFE). Our stack consists of three components: i. a verified compiler (CircGen) that translates C programs into Boolean circuits; ii. a verified implementation of Yao's SFE protocol based on garbled circuits and oblivious transfer; and iii. transparent application integration and communications via FRESCO, an open-source framework for secure multiparty computation (MPC). CircGen is a general purpose tool that builds on CompCert, a verified optimizing compiler for C. It can be used in arbitrary Boolean circuit-based cryptography deployments. The security of our SFE protocol implementation is formally verified using EasyCrypt, a tool-assisted framework for building high-confidence cryptographic proofs, and it leverages a new formalization of garbled circuits based on the framework of Bellare, Hoang, and Rogaway (CCS 2012). We conduct a practical evaluation of our approach, and conclude that it is competitive with state-of-the-art (unverified) approaches. Our work provides concrete evidence of the feasibility of building efficient, verified, implementations of higher-level cryptographic systems. All our development is publicly available.

Abstract. In this paper we show how Isolated Execution Environments (IEE) offered by novel commodity hardware such as Intel's SGX provide a new path to constructing general secure multiparty computation (MPC) protocols. Our protocol is intuitive and elegant: it uses code within an IEE to play the role of a trusted third party (TTP), and the attestation guarantees of SGX to bootstrap secure communications between participants and the TTP. The load of communications and computations on participants only depends on the size of each party's inputs and outputs and is thus small and independent from the intricacies of the functionality to be computed. The remaining computational load-essentially that of computing the functionality -is moved to an untrusted party running an IEE-enabled machine, an attractive feature for Cloud-based scenarios. Our rigorous modular security analysis relies on the novel notion of labeled attested computation which we put forth in this paper. This notion is a convenient abstraction of the kind of attestation guarantees one can obtain from trusted hardware in multi-user scenarios. Finally, we present an extensive experimental evaluation of our solution on SGXenabled hardware. Our implementation is open-source and it is functionality agnostic: it can be used to securely outsource to the Cloud arbitrary off-the-shelf collaborative software, such as the one employed on financial data applications, enabling secure collaborative execution over private inputs provided by multiple parties. IntroductionSecure multiparty computation (MPC) allows a set of mutually distrusting parties to collaboratively carry out a computation that involves their private inputs. The security guarantee that parties get are essentially those provided by carrying out the same computation using a Trusted Third Party (TTP). The computations to be carried out range from simple functionalities, for example where a party commits to a secret value and later on reveals it; or they can be highly complex, for example running sealed bid auctions [11] or bank customer benchmarking [20]. Most of the existent approaches are software only. The trust barrier between parties is overcome using cryptographic techniques that permit computing over encrypted and/or secret-shared data [35,28,19]. Another approach first studied by Katz [31] formalizes a trusted hardware assumptionwhere users have access to tamper-proof tokens on which they can load arbitrary codethat is sufficient to bootstrap universally composable MPC.Broadly speaking, this work fits within the same category as that by Katz [15]. However, our starting point is a novel real-world form of trusted hardware that is currently shipped on commodity PCs: Intel's Software Guard Extensions [30]. Our goal is to leverage this hardware to significantly reduce the computational costs of practical secure computation protocols. The main security capability that such hardware offers are Isolated Execution Environments (IEE) -a powerful tool for boosting trust in remote systems under the tot...

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We study the problem of privacy-preserving proofs on authenticated data, where a party receives data from a trusted source and is requested to prove computations over the data to third parties in a correct and private way, i.e., the third party learns no information on the data but is still assured that the claimed proof is valid. Our work particularly focuses on the challenging requirement that the third party should be able to verify the validity with respect to the specific data authenticated by the source-even without having access to that source. This problem is motivated by various scenarios emerging from several application areas such as wearable computing, smart metering, or general business-to-business interactions. Furthermore, these applications also demand any meaningful solution to satisfy additional properties related to usability and scalability. In this paper, we formalize the above three-party model, discuss concrete application scenarios, and then we design, build, and evaluate ADSNARK, a nearly practical system for proving arbitrary computations over authenticated data in a privacy-preserving manner. ADSNARK improves significantly over state-of-the-art solutions for this model. For instance, compared to corresponding solutions based on Pinocchio (Oakland'13), ADSNARK achieves up to 25× improvement in proof-computation time and a 20× reduction in prover storage space.

Abstract. We propose a new hybrid protocol for cryptographically secure biometric authentication. The main advantages of the proposed protocol over previous solutions can be summarised as follows: (1) potential for much better accuracy using different types of biometric signals, including behavioural ones; and (2) improved user privacy, since user identities are not transmitted at any point in the protocol execution. The new protocol takes advantage of state-of-the-art identification classifiers, which provide not only better accuracy, but also the possibility to perform authentication without knowing who the user claims to be. Cryptographic security is based on the Paillier public key encryption scheme.