International Association for Cryptologic Research

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2014-02-27
04:17 [Pub][ePrint]

The notion of Zero Knowledge introduced by Goldwasser, Micali, and Rackoff in STOC 1985 is fundamental in Cryptography. Motivated by conceptual and practical reasons, this notion has been explored under stronger definitions. We will consider the following two main strengthened notions.

-- Statistical Zero Knowledge: here the zero-knowledge property will last forever, even in case in future the adversary will have unlimited power.

-- Concurrent Non-Malleable Zero Knowledge: here the zero-knowledge property is combined with non-transferability and the adversary fails in mounting a concurrent man-in-the-middle attack aiming at transferring zero-knowledge proofs/arguments.

Besides the well-known importance of both notions, it is still unknown whether one can design a zero-knowledge protocol that satisfies both notions simultaneously.

In this work we shed light on this question in a very strong sense. We show a {\\em statistical concurrent non-malleable} zero-knowledge argument system for NP with a {\\em black-box} simulator-extractor.

04:17 [Pub][ePrint]

We consider the case where an authenticated encryption scheme outputs the decrypted plaintext before successful verification. This scenario raises many security issues, and is highlighted in the upcoming CAESAR competition. It arises for example when devices have insufficient memory to store the entire plaintext, or when the decrypted plaintext needs to be processed early due to real-time requirements. Firstly, we formalize the releasing unverified plaintext (RUP) setting. To achieve privacy in this setting, we propose using plaintext awareness (PA) along with IND-CPA. An authenticated encryption scheme is PA if there exists a plaintext extractor for every adversary. The plaintext extractor does not know the secret key, but tries to fool the adversary by mimicking the decryption oracle. The release of unverified plaintext then becomes harmless, because it is infeasible to distinguish between answers from the real decryption oracle and from the plaintext extractor. We introduce two notions of plaintext awareness in the symmetric-key setting (PA1 and PA2), and show implications and separations between PA1, PA2, and existing notions. To achieve integrity of the ciphertexts, INT-CTXT in the RUP setting is required, which we refer to as INT-RUP. These security notions are then used to make a classification of symmetric-key schemes in the RUP setting. We analyze existing authenticated encryption schemes in this setting, and provide solutions to fix insecure schemes.

04:17 [Pub][ePrint]

In this paper we propose an efficient technique to compute algebraic degree of an S-box (minimum of algebraic degrees of its component functions). Using our technique we have calculated algebraic degree of a $26\\times 64$ S-box.

04:17 [Pub][ePrint]

Coherent light, as produced by lasers, gives rise to an intrinsic noise, known as quantum noise, optical noise or shot noise. AlphaEta is a protocol which exploits this physical phenomenon to obtain secure data encryption or key distribution over a fiber-optic channel

in the presence of an eavesdropper. In this paper we focus on the cryptographic aspects of AlphaEta and its variants. Moreover, we propose a new protocol for which we can provide a rigorous proof

that the eavesdropper obtains neglible information. In comparison to single-photon quantum cryptography, AlphaEta provide much higher throughputs combined with a well-known technology.

2014-02-25
16:17 [Pub][ePrint]

We calculate the probability of success of block-hiding mining strategies in bitcoin-like networks.

These strategies involve building a secret branch of the block-tree and publishing it opportunistically, aiming to replace the top of the main branch and rip the reward associated with the secretly mined blocks. We identify two types of block-hiding strategies and chart the parameter space where those are more beneficial than the standard mining strategy described in Nakamoto\'s paper.

Our analysis suggests a generalization of the notion of the relative hashing power as a measure for a miner\'s influence on the network. Block-hiding strategies are beneficial only when this measure of influence exceeds a certain threshold.

2014-02-24
04:17 [Pub][ePrint]

We propose a simple and efficient sorting algorithm for secure multi-party computation (MPC). The algorithm is designed to be efficient when the number of parties and the size of the underlying field are small. For a constant number of parties and a field with a constant size, the algorithm has $O(\\gm\\log\\gm)$ communication complexity, which is asymptotically the same as the best previous algorithm but achieves $O(1)$ round complexity, where $\\gm$ is the number of items. The algorithm is constructed with the help of a new technique called shuffle-and-reveal.\'\' This technique can be seen as an analogue of the frequently used technique of add random number and reveal.\'\' The feasibility of our algorithm is demonstrated by an implementation on an MPC scheme based on Shamir\'s secret-sharing scheme with three parties and corruption tolerance of $1$. Our implementation sorts 1 million 32-bit word secret-shared values in 197 seconds.

04:17 [Pub][ePrint]

In this paper, a new way to construct cryptographic hash function is given. The cryptographic hash function is generalized to uncertain function which has various specific function forms. When computing hash value, the specific form of the function is determined by the message, but the codebreaker cannot know the message, and hence cannot know the specific form of random function. This provides a new kind of one-wayness, the one-wayness of the specific function makes the breaking of hash is very difficult because in most cryptographic analysis of hash function, the function should be known and fixed. As fixed function is just a special case of uncertain function, when the function is uncertain, we obviously have more choices and can choose more secure function.

Keywords:I.Introduction

04:17 [Pub][ePrint]

This paper suggests a model and a definition for forward-secure authenticated key exchange (AKE) protocols, which can be satisfied without depending on the Diffie-Hellman assumption. Protocols conforming to our model can be highly efficient, since they do not require the resource-intensive modular exponentiations of the Diffie-Hellman protocol. The basic idea is to use key-evolving schemes (KES), where the long-term keys of the system get updated regularly and irreversibly. We also introduce a protocol, called FORSAKES, and prove rigorously that it is a forward-secure AKE protocol in our model. FORSAKES is a very efficient protocol, and can be implemented by merely using hash functions.

04:17 [Pub][ePrint]

A secret sharing scheme is non-perfect if some subsets of participants cannot recover the secret value but have some information about it. This work is dedicated to the search of efficient non-perfect secret sharing schemes. The efficiency is measured by means of the information ratio, the ratio between the maximum length of the shares and the length of the secret value.

In order to study perfect and non-perfect secret sharing schemes with all generality, we describe the structure of the schemes through their access function, a real function that measures the amount of information that every subset of participants knows about the secret value. We present new tools for the construction of secret sharing schemes. In particular, we construct a secret sharing scheme for every access function.

We extend the connections between polymatroids and perfect secret sharing schemes to the non-perfect ones to find new results on the information ratio. We find a new lower bound on the information ratio that is better than the ones previously known. In particular, this bound is tight for uniform access functions. The access function of a secret sharing scheme is uniform if all participants play the same role in a scheme (e.g. ramp secret sharing schemes). Moreover, we construct a secret sharing scheme with optimal information ratio for every rational uniform access function.

04:17 [Pub][ePrint]