Randomized Secure Two-Party Computation for Modular Conversion, Zero Test, Comparison, MOD and Exponentiation

When secure arithmetic is required, computation based on secure multiplication (\MULT) is much more efficient than computation based on secure boolean circuits. However, a typical application can also require other building blocks, such as comparison, exponentiation and the modulo (MOD) operation. Secure solutions for these functions proposed in the literature rely on bit-decomposition or other bit-oriented methods, which require $O(\ell)$ \MULTs for $\ell$-bit inputs. In the absence of a known bit-length independent solution, the complexity of the whole computation is often dominated by these non-arithmetic functions. To resolve the above problem, we start with a general modular conversion, which converts secret shares over distinct moduli. For this, we proposed a probabilistically correct protocol for this with a complexity that is independent of $\ell$. Then, we show that when these non-arithmetic functions are based on secure modular conversions, they can be computed in constant rounds and $O(k)$ \MULTs, where $k$ is a parameter for an error rate of $2^{-\Omega(k)}$. To promote our protocols to be actively secure, we apply $O(k)$ basic zero-knowledge proofs, which cost at most $O(k)$ exponentiation computation, $O(1)$ rounds and $O(k(\ell+\kappa))$ communication bits, where $\kappa$ is the security parameter used in the commitment scheme

RSA Power Analysis Obfuscation: A Dynamic FPGA Architecture

The modular exponentiation operation used in popular public key encryption schemes, such as RSA, has been the focus of many side channel analysis (SCA) attacks in recent years. Current SCA attack countermeasures are largely static. Given sufficient signal-to-noise ratio and a number of power traces, static countermeasures can be defeated, as they merely attempt to hide the power consumption of the system under attack. This research develops a dynamic countermeasure which constantly varies the timing and power consumption of each operation, making correlation between traces more difficult than for static countermeasures. By randomizing the radix of encoding for Booth multiplication and randomizing the window size in exponentiation, this research produces a SCA countermeasure capable of increasing RSA SCA attack protection

マルチパーティー計算の効率的な構成と実装

電気通信大学201

Secure Quantized Training for Deep Learning

We have implemented training of neural networks in secure multi-party computation (MPC) using quantization commonly used in the said setting. To the best of our knowledge, we are the first to present an MNIST classifier purely trained in MPC that comes within 0.2 percent of the accuracy of the same convolutional neural network trained via plaintext computation. More concretely, we have trained a network with two convolution and two dense layers to 99.2% accuracy in 25 epochs. This took 3.5 hours in our MPC implementation (under one hour for 99% accuracy).Comment: 17 page

Lightweight secure integer comparison

We solve the millionaires problem in the semi-trusted model with homomorphic encryption without using intermediate decryptions. This leads to the computationally least expensive solution with homomorphic encryption so far, with a low bandwidth and very low storage complexity. The number of modular multiplications needed is less than the number of modular multiplications needed for one Pallier encryption. The output of the protocol can be either publicly known, encrypted, or secret-shared. The private input of the first player is computationally secure towards the second player, and the private input of the second player is even unconditionally secure towards the first player. We also introduce an efficient client-server solution for the millionaires problem with similar security properties

AES Side-Channel Countermeasure using Random Tower Field Constructions

International audienceMasking schemes to secure AES implementations against side-channel attacks is a topic of ongoing research. The most sensitive part of the AES is the non-linear SubBytes operation, in particular, the inversion in GF(2^8), the Galois field of 2^8 elements. In hardware implementations, it is well known that the use of the tower of extensions GF(2) ⊂ GF(2^2) ⊂ GF(2^4) ⊂ GF(2^8) leads to a more efficient inversion. We propose to use a random isomorphism instead of a fixed one. Then, we study the effect of this randomization in terms of security and efficiency. Considering the field extension GF(2^8)/GF(2^4), the inverse operation leads to computation of its norm in GF(2^4). Hence, in order to thwart side-channel attack, we manage to spread the values of norms over GF(2^4). Combined with a technique of boolean masking in tower fields, our countermeasure strengthens resistance against first-order differential side-channel attacks

Efficient secure comparison in the dishonest majority model

Secure comparison (SC) is an essential primitive in Secure Multiparty Computation (SMC) and a fundamental building block in Privacy-Preserving Data Analytics (PPDA). Although secure comparison has been studied since the introduction of SMC in the early 80s and many protocols have been proposed, there is still room for improvement, especially providing security against malicious adversaries who form the majority among the participating parties. It is not hard to develop an SC protocol secure against malicious majority based on the current state-of-the-art SPDZ framework. SPDZ is designed to work for arbitrary polynomially-bounded functionalities; it may not provide the most efficient SMC implementation for a specific task, such as SC. In this thesis, we propose a novel and efficient compiler specifically designed to convert most existing SC protocols with semi-honest security into the ones secure against the dishonest majority (malicious majority). We analyze the security of the proposed solutions using the real-ideal paradigm. Moreover, we provide computation and communication complexity analysis. Comparing to the current state-of-the-art SC protocols Rabbit and edaBits, our design offers significant performance gain. The empirical results show that the proposed solution is at least 5 and 10 times more efficient than Rabbit in run-time and communication cost respectively.Includes bibliographical references

Garbling Gadgets for Boolean and Arithmetic Circuits

We present simple, practical, and powerful new techniques for garbled circuits. These techniques result in significant concrete and asymptotic improvements over the state of the art, for several natural kinds of computations. For arithmetic circuits over the integers, our construction results in garbled circuits with {\em free} addition, weighted threshold gates with cost independent of fan-in, and exponentiation by a fixed exponent with cost independent of the exponent. For boolean circuits, our construction gives an {\em exponential} improvement over the state of the art for threshold gates (including AND/OR gates) of high fan-in. Our construction can be efficiently instantiated with practical symmetric-key primitives (e.g., AES), and is proven secure under similar assumptions to that of the Free-XOR garbling scheme (Kolesnikov \& Schneider, ICALP 2008). We give an extensive comparison between our scheme and state-of-the-art garbling schemes applied to boolean circuits

Privacy Preserving Cryptographic Protocols for Secure Heterogeneous Networks

Disertační práce se zabývá kryptografickými protokoly poskytující ochranu soukromí, které jsou určeny pro zabezpečení komunikačních a informačních systémů tvořících heterogenní sítě. Práce se zaměřuje především na možnosti využití nekonvenčních kryptografických prostředků, které poskytují rozšířené bezpečnostní požadavky, jako je například ochrana soukromí uživatelů komunikačního systému. V práci je stanovena výpočetní náročnost kryptografických a matematických primitiv na různých zařízeních, které se podílí na zabezpečení heterogenní sítě. Hlavní cíle práce se zaměřují na návrh pokročilých kryptografických protokolů poskytujících ochranu soukromí. V práci jsou navrženy celkově tři protokoly, které využívají skupinových podpisů založených na bilineárním párování pro zajištění ochrany soukromí uživatelů. Tyto navržené protokoly zajišťují ochranu soukromí a nepopiratelnost po celou dobu datové komunikace spolu s autentizací a integritou přenášených zpráv. Pro navýšení výkonnosti navržených protokolů je využito optimalizačních technik, např. dávkového ověřování, tak aby protokoly byly praktické i pro heterogenní sítě.The dissertation thesis deals with privacy-preserving cryptographic protocols for secure communication and information systems forming heterogeneous networks. The thesis focuses on the possibilities of using non-conventional cryptographic primitives that provide enhanced security features, such as the protection of user privacy in communication systems. In the dissertation, the performance of cryptographic and mathematic primitives on various devices that participate in the security of heterogeneous networks is evaluated. The main objectives of the thesis focus on the design of advanced privacy-preserving cryptographic protocols. There are three designed protocols which use pairing-based group signatures to ensure user privacy. These proposals ensure the protection of user privacy together with the authentication, integrity and non-repudiation of transmitted messages during communication. The protocols employ the optimization techniques such as batch verification to increase their performance and become more practical in heterogeneous networks.

Efficient cryptosystem for universally verifiable mixnets

Projecte final de carrera realitzat en col.laboració amb Scytl Secure Electronic Votin