International Association for Cryptologic Research

# IACR News Central

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2014-02-04
19:17 [Pub][ePrint]

In the last few years the efficiency of secure multi-party computation (MPC) increased in several orders of magnitudes. However, this alone might not be enough if we want MPC protocols to be used in practice.

A crucial property that is needed in many applications is that everyone can check that a given (secure) computation was performed correctly -- even in the extreme case where all the parties involved in the computation are corrupted, and even if the party who wants to verify the result was not involved. An obvious example of this is electronic voting, but also in many types of auctions one may want independent verification of the result. Traditionally, this is achieved by using non-interactive zero-knowledge proofs.

A recent trend in MPC protocols is to have a more expensive preprocessing phase followed by a very efficient online phase, e.g., the recent so-called SPDZ protocol by Damgård et al. Applications such as voting and some auctions are perfect applications for these protocols, as the parties usually know well in advance when the computation will take place, and using those protocols allows us to use only cheap information theoretic primitives in the actual computation. Unfortunately no protocol of the SPDZ type supports an audit phase.

In this paper we formalize the concept of publicly auditable secure computation and provide an enhanced version of the SPDZ protocol where, even if all the servers are corrupted, anyone with access to the transcript of the protocol can check that the output is indeed correct. Most importantly, we do so without compromising the performance of SPDZ i.e., the cost of our online phase is the same as that of SPDZ, up to a small constant factor of about two.

19:17 [Pub][ePrint]

Bitcoin is a peer-to-peer (p2p) electronic cash system that

uses a distributed timestamp service to record transactions in a public ledger (called the Blockchain). A critical component of Bitcoin\'s success is the decentralized nature of its architecture, which does not require or even support the establishment of trusted authorities. Yet the absence of certification creates obstacles to its wider acceptance in e-commerce and official uses. We propose a certification system for Bitcoin that offers: a) an opt-in guarantee to send and receive bitcoins only to/ from certified users; b) control of creation of bitcoins addresses (certified users) by trusted authorities.

Our proposal may encourage the adoption of Bitcoin in different scenarios that require an officially recognized currency, such

as tax payments--often an integral part of e-commerce transactions.

19:17 [Pub][ePrint]

We propose Mixcoin, a protocol to facilitate anonymous payments using the Bitcoin currency system. We build on the emergent phenomenon of currency mixes, adding an accountability mechanism to expose theft. Unlike other proposals to improve anonymity in Bitcoin, our scheme can be deployed immediately with no changes to Bitcoin itself. We demonstrate that incentives of mixes and clients can be aligned to ensure that rational mixes will not steal from clients. We contrast mixing for financial anonymity with better-studied communication mixes, demonstrating important and subtle new attacks.

19:17 [Pub][ePrint]

Most lattice-based cryptographic schemes which enjoy a security proof suffer from huge key sizes and heavy computations. This is also true for the simpler case of identification protocols. Recent progress on ideal lattices has significantly improved the efficiency, and made it possible to implement practical lattice-based cryptography on constrained devices like FPGAs and smart phones. However, to the best of our knowledge, no previous attempts were made to implement lattice-based schemes on smart cards. In this paper, we report the results of our implementation of several state-of-the-art and highly-secure lattice-based identification protocols on smart cards and microcontrollers. Our results show that only a few of such protocols fit into the limitations of these devices. We also discuss the implementation challenges and techniques to perform lattice-based cryptography on constrained devices, which may be of independent interest.

19:17 [Pub][ePrint]

A recent trend in cryptography is to formally show the leakage resilience of cryptographic implementations in a given leakage model. One of the most prominent leakage models -- the so-called bounded leakage model -- assumes that the amount of leakage is a-priori bounded. Unfortunately, it has been pointed out that the assumption of bounded leakages is hard to verify in practice. A more realistic assumption is to assume that leakages are sufficiently noisy, following the engineering observation that real-world physical leakages are inherently noisy. While the noisy leakage assumption has first been studied in the seminal work of Chari et al. (CRYPTO 99), the recent work of Prouff and Rivain (Eurocrypt 2013) provides the first analysis of a full masking scheme under a physically motivated noise model. In particular, the authors show that a block-cipher implementation that uses an additive masking scheme is secure against noisy leakages. Unfortunately, the security analysis of Prouff and Rivain has three important shortcomings: (1) it requires leak-free gates, (2) it considers a restricted adversarial model (random message attacks), and (3) the security proof has limited application for cryptographic settings. In this work, we provide an alternative security proof in the same noisy model that overcomes these three challenges. We achieve this goal by a new reduction from noisy leakage to the important theoretical model of probing adversaries (Ishai et al~ -- CRYPTO 2003). Our work can be viewed as a next step of closing the gap between theory and practice in leakage resilient cryptography: while our security proofs heavily rely on concepts of theoretical cryptography, we solve problems in practically motivated leakage models.

16:17 [Pub][ePrint]

The article proposes one-pass authenticated key establishment protocol

in random oracles for Wireless Sensor Networks. Security of the protocol relies on Computational Diffie-Hellman Problem on Bilinear Pairings. In one-pass key establishment protocol, the initiator computes a session key and a related message. The key token is to be sent to the intended receiver using receiver\'s public key and sender

secret key. From the received key token the receiver compute the session key, which is the same as the one computed by the sender, using sender public key and receiver\'s secret key. Because of low communication overhead, the scheme is better suited for Wireless Sensor Networks(WSNs) than the traditional key establishment protocol to establish the session key between two adjacent nodes.

16:17 [Pub][ePrint]

In recent years, \\emph{lattice-based} cryptography has been recognized

for its many attractive properties, such as strong provable security

guarantees and apparent resistance to quantum attacks, flexibility for

realizing powerful tools like fully homomorphic encryption, and high

asymptotic efficiency. Indeed, several works have demonstrated that

for basic tasks like encryption and authentication, lattice-based

primitives can have performance competitive with (or even surpassing)

those based on classical mechanisms like RSA or Diffie-Hellman.

However, there still has been relatively little work on developing

lattice cryptography for deployment in \\emph{real-world} cryptosystems

and protocols.

In this work we take a step toward that goal, by giving efficient

and practical lattice-based protocols for key transport, encryption,

and authenticated key exchange that are suitable as drop-in\'\'

components for proposed Internet standards and other open protocols.

The security of all our proposals is provably based (sometimes in the

random-oracle model) on the well-studied learning with errors over

rings\'\' problem, and hence on the conjectured worst-case hardness of

problems on ideal lattices (against quantum algorithms).

One of our main technical innovations (which may be of independent

interest) is a simple, low-bandwidth \\emph{reconciliation} technique

that allows two parties who approximately agree\'\' on a secret value

to reach \\emph{exact} agreement, a setting common to essentially all

lattice-based encryption schemes. Our technique reduces the

ciphertext length of prior (already compact) encryption schemes nearly

twofold, at essentially no cost.% in security, key size, or runtime.

16:17 [Pub][ePrint]

In the last decade, pairing-based cryptography has been the most intensively studied subject in the cryptography field. Various optimization techniques have been developed to speed up the pairing computation. However, implementing a pairing-based cryptosystem in resource constrained devices has been less tried. Moreover, due to progress on solving the discrete logarithm problem, those implementations are no longer safe to use. In this paper, we report an implementation of a couple of pairing-based cryptosystems at a high security level on a 32-bit microcontroller in a USB token. It shows that USB tokens supporting secure pairing-based cryptosystems are viable.

06:15 [Event][New]

From September 29 to September 30

2014-02-03
21:56 [Job][New]

The Vernam Group for Security and Privacy at WPI in Worcester, MA has open PhD positions in applied cryptology. In particular there are two openings in side channel analysis and leakage resilient implementation.

Candidates should have a Master’s degree in electronics, computer science or applied mathematics, with strong interest in algorithms and signal processing. Prior experience in side channel analysis and embedded software or hardware design is an asset.

We offer a competitive salary and an international cutting-edge research program in an attractive working environment. WPI is one of the highest-ranked technical colleges in the US. Located in the greater Boston area, it maintains close interaction with many of the nearby universities and companies.

12:54 [Event][New]

Submission: 28 May 2014
From August 14 to August 15