Decryption phase in Norwegian electronic voting

We describe an efficient and secure decryption protocol to the Norwegian Internet voting project. We first adapt Groth’s shuffle-decryption from 2010 to our purpose, and we prove all security properties in the random oracle model. We then describe the complete decryption algorithm, and prove that it maintains the security of the rest of the protocol

The Norwegian Internet Voting Protocol: A new Instantiation

The Norwegian government ran trials of internet remote voting during the 2011 municipal elections and the 2013 parliamentary elections. From a simplified version of the voting protocol used there, the essential cryptographic operations of the voting protocol has been put together into a cryptosystem in which one can build the voting protocol on top of. This paper proposes a new instantiation of the underlying cryp- tosystem, improving our confidence in the security of the cryptosys- tem. The new instantiation is mostly similar to a previously defined instantiation, but allows parts of the security proof to be significantly improved

Analysis of an internet voting protocol

The Norwegian government is planning trials of internet voting in the 2011 local government elections. We describe and analyse the cryptographic protocol that will be used. In our opinion, the protocol is suitable for trials of internet voting, even though it is not perfect. This paper is a second1 step in an ongoing evaluation of the cryptographic protocol

The Norwegian Internet Voting Protocol

The Norwegian government ran a trial of internet remote voting during the 2011 local government elections, and will run another trial during the 2013 parliamentary elections. A new cryptographic voting protocol will be used, where so-called return codes allow voters to verify that their ballots will be counted as cast. This paper discusses this cryptographic protocol, and in particular the ballot submission phase. The security of the protocol relies on a novel hardness assumption similar to Decision Diffie-Hellman. While DDH is a claim that a random subgroup of a non-cyclic group is indistinguishable from the whole group, our assumption is related to the indistinguishability of certain special subgroups. We discuss this question in some detail

Secure Computation in Heterogeneous Environments: How to Bring Multiparty Computation Closer to Practice?

Many services that people use daily require computation that depends on the private data of multiple parties. While the utility of the final result of such interactions outweighs the privacy concerns related to output release, the inputs for such computations are much more sensitive and need to be protected. Secure multiparty computation (MPC) considers the question of constructing computation protocols that reveal nothing more about their inputs than what is inherently leaked by the output. There have been strong theoretical results that demonstrate that every functionality can be computed securely. However, these protocols remain unused in practical solutions since they introduce efficiency overhead prohibitive for most applications. Generic multiparty computation techniques address homogeneous setups with respect to the resources available to the participants and the adversarial model. On the other hand, realistic scenarios present a wide diversity of heterogeneous environments where different participants have different available resources and different incentives to misbehave and collude. In this thesis we introduce techniques for multiparty computation that focus on heterogeneous settings. We present solutions tailored to address different types of asymmetric constraints and improve the efficiency of existing approaches in these scenarios. We tackle the question from three main directions: New Computational Models for MPC - We explore different computational models that enable us to overcome inherent inefficiencies of generic MPC solutions using circuit representation for the evaluated functionality. First, we show how we can use random access machines to construct MPC protocols that add only polylogarithmic overhead to the running time of the insecure version of the underlying functionality. This allows to achieve MPC constructions with computational complexity sublinear in the size for their inputs, which is very important for computations that use large databases. We also consider multivariate polynomials which yield more succinct representations for the functionalities they implement than circuits, and at the same time a large collection of problems are naturally and efficiently expressed as multivariate polynomials. We construct an MPC protocol for multivariate polynomials, which improves the communication complexity of corresponding circuit solutions, and provides currently the most efficient solution for multiparty set intersection in the fully malicious case. Outsourcing Computation - The goal in this setting is to utilize the resources of a single powerful service provider for the work that computationally weak clients need to perform on their data. We present a new paradigm for constructing verifiable computation (VC) schemes, which enables a computationally limited client to verify efficiently the result of a large computation. Our construction is based on attribute-based encryption and avoids expensive primitives such as fully homomorphic encryption andprobabilistically checkable proofs underlying existing VC schemes. Additionally our solution enjoys two new useful properties: public delegation and verification. We further introduce the model of server-aided computation where we utilize the computational power of an outsourcing party to assist the execution and improve the efficiency of MPC protocols. For this purpose we define a new adversarial model of non-collusion, which provides room for more efficient constructions that rely almost completely only on symmetric key operations, and at the same time captures realistic settings for adversarial behavior. In this model we propose protocols for generic secure computation that offload the work of most of the parties to the computation server. We also construct a specialized server-aided two party set intersection protocol that achieves better efficiencies for the two participants than existing solutions. Outsourcing in many cases concerns only data storage and while outsourcing the data of a single party is useful, providing a way for data sharing among different clients of the service is the more interesting and useful setup. However, this scenario brings new challenges for access control since the access control rules and data accesses become private data for the clients with respect to the service provide. We propose an approach that offers trade-offs between the privacy provided for the clients and the communication overhead incurred for each data access. Efficient Private Search in Practice - We consider the question of private search from a different perspective compared to traditional settings for MPC. We start with strict efficiency requirements motivated by speeds of available hardware and what is considered acceptable overhead from practical point of view. Then we adopt relaxed definitions of privacy, which still provide meaningful security guarantees while allowing us to meet the efficiency requirements. In this setting we design a security architecture and implement a system for data sharing based on encrypted search, which achieves only 30% overhead compared to non-secure solutions on realistic workloads

A Latency-Free Election Scheme

We motivate and describe the problem of finding protocols for multiparty computations that only use a single broadcast round per computation (latency-free computations). We show that solutions exists for one multiparty computation problem, that of elections, and more generally, addition in certain groups. The protocol construction is based on an interesting pseudo-random function family with a novel property