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TERMinator Suite: Benchmarking Privacy-Preserving Architectures

Fri, 12/22/2017 - 10:46
Security and privacy are fundamental objectives characterizing contemporary cloud computing. Despite the wide adoption of encryption for protecting data in transit and at rest, data in use remains unencrypted inside cloud processors and memories, as computation is not applicable on encrypted values. This limitation introduces security risks, as unencrypted values can be leaked through side-channels or hardware Trojans. To address this problem, encrypted architectures have recently been proposed, which leverage homomorphic encryption to natively process encrypted data using datapaths of thousands of bits. In this case, additional security protections are traded for higher performance penalties, which drives the need for more efficient architectures. In this work, we develop benchmarks specifically tailored to encrypted computers, to enable comparisons across different architectures. Our benchmark suite, dubbed TERMinator, is unique as it avoids 'termination problems' that prohibit making control-flow decisions and evaluating early termination conditions based on encrypted data, as these can leak information. Contrary to generic suites that ignore the fundamental challenges of encrypted computation, our algorithms are tailored to the security primitives of the target encrypted architecture, such as the existence of branching oracles. In our experiments, we compiled our benchmarks for the Cryptoleq architecture and evaluated their performance for a range of security parameters.

Efficient RSA Key Generation and Threshold Paillier in the Two-Party Setting

Fri, 12/22/2017 - 07:38
The problem of generating an RSA composite in a distributed manner without leaking its factorization is particularly challenging and useful in many cryptographic protocols. Our first contribution is the first non-generic fully simulatable protocol for distributively generating an RSA composite with security against malicious behavior. Our second contribution is complete Paillier [Pai99] threshold encryption scheme in the two-party setting with security against malicious behavior. Furthermore, we describe how to extend our protocols to the multiparty setting with dishonest majority. Our RSA key generation is comprised of the following: (i) a distributed protocol for generation of an RSA composite, and (ii) a biprimality test for verifying the validity of the generated composite. Our Paillier threshold encryption scheme uses the RSA composite as public key and is comprised of: (i) a distributed generation of the corresponding secret-key shares and, (ii) a distributed decryption protocol for decrypting according to Paillier.

The Lightest 4x4 MDS Matrices over $GL(4,\mathbb{F}_2)$

Thu, 12/21/2017 - 04:13
Maximal distance separable (MDS) matrices are important components for block ciphers. In this paper, we present an algorithm for searching $4\times 4$ MDS matrices over GL(4, $\mathbb{F}_2$). By this algorithm, we find all the lightest MDS matrices have only 10 XOR counts. Besides, all these lightest MDS matrices are classified to 3 types, and some necessary and sufficient conditions are presented for them as well. Some theoretical results can be generalized to the case $GL(m,\mathbb{F}_2)$ easily, and $4 \times 4$ MDS matrices with 10 XOR counts can be constructed directly.

Asynchronous provably-secure hidden services

Wed, 12/20/2017 - 13:32
The client-server architecture is one of the most widely used in the Internet for its simplicity and flexibility. In practice the server is assigned a public address so that its services can be consumed. This makes theserver vulnerable to a number of attacks such as Distributed Denial of Service (DDoS), censorship from authoritarian governments or exploitationof software vulnerabilities. In this work we propose an asynchronous protocol for allowing a client to issue requests to a server without revealing any information about the location of the server. In addition, our solution reveals limited information about the network topology, leaking only the distance from the client to the corrupted participants. We also provide a simulation-based security definition capturing the requirement described above. Our protocol is secure in the semi-honest model against any number of colluding participants, and has linear communication complexity. Finally, we extend our solution to handle active adversaries. We show that malicious participants can only trigger a premature termination of the protocol, in which case they are identified. For this solution the communication complexity becomes quadratic. To the best of our knowledge our solution is the first asynchronous protocol that provides strong security guarantees.

How to Use Metaheuristics for Design of Symmetric-Key Primitives

Wed, 12/20/2017 - 08:40
The ultimate goal of designing a symmetric-key cryptographic primitive often can be formulated as an optimization problem. So far, these problems mainly have been solved with trivial algorithms such as brute force or random search. We show that a more advanced and equally versatile class of search algorithms, called metaheuristics, can help to tackle optimization problems related to design of symmetric-key primitives. We use two nature-inspired metaheuristics, simulated annealing and genetic algorithm, to optimize in terms of security the components of two recent cryptographic designs, SKINNY and AES-round based constructions. The positive outputs of the optimization suggest that metaheuristics are non-trivial tools, well suited for automatic design of primitives.

Exploring Potential 6LoWPAN Traffic Side Channels

Tue, 12/19/2017 - 16:34
The Internet of Things (IoT) has become a reality: small connected devices feature in everyday objects including childrens' toys, TVs, fridges, heating control units, etc. Supply chains feature sensors throughout, and significant investments go into researching next-generation healthcare, where sensors monitor wellbeing. A future in which sensors and other (small) devices interact to create sophisticated applications seems just around the corner. All of these applications have a fundamental need for security and privacy and thus cryptography is deployed as part of an attempt to secure them. In this paper we explore a particular type of flaw, namely side channel information, on the protocol level that can exist despite the use of cryptography. Our research investigates the potential for utilising packet length and timing information (both are easily obtained) to extract interesting information from a system. We find that using these side channels we can distinguish between devices, different programs running on the same device including which sensor is accessed. We also find it is possible to distinguish between different types of ICMP messages despite the use of encryption. Based on our findings, we provide a set of recommendations to efficiently mitigate these side channels in the IoT context.

Linear Regression Side Channel Attack Applied on Constant XOR

Tue, 12/19/2017 - 08:52
Linear regression side channel attack (LRA) used to be known as a robust attacking method as it makes use of independent bits leakage. This leakage assumption is more general than Hamming weight/ Hamming distance model used in correlation power attack (CPA). However, in practice, Hamming weight and Hamming distance model suit most devices well. In this paper, we restudy linear regression attack under Hamming weight/ Hamming distance model and propose our novel LRA methods. We find that in many common scenarios LRA is not only an alternative but also a more efficient tool compared with CPA. Two typical cases are recovering keys with XOR operation leakage and chosen plaintext attack on block ciphers with leakages from round output. Simulation results are given to compare with traditional CPA in both cases. Our LRA method achieves up to 400% and 300% improvements for corresponding case compared with CPA respectively. Experiments with AES on SAKURA-G board also prove the efficiency of our methods in practice where 128 key bits are recovered with 1500 traces using XOR operation leakage and one key byte is recovered with only 50 chosen-plaintext traces in the other case.

Composable and Robust Outsourced Storage

Tue, 12/19/2017 - 06:45
The security of data outsourcing mechanisms has become a crucial aspect of today's IT infrastructures and are the cryptographic foundations of real-world applications. The very fundamental goals are ensuring storage integrity and auditability, confidentiality, and access pattern hiding, as well as combinations of all of them. Despite sharing a common setting, security analyses of these tasks are often performed in a stand-alone fashion expressed in different models, which makes it hard to assess the overall security of a protocol or application involving several security schemes at once. In this work, we fill this gap and propose a composable framework suitable to capture various aspects of outsourced storage security and its applications. We instantiate the basic client-server setting in this model, where the goal of the honest client is to retain security in the presence of a malicious server. Three specific contributions of this paper are: 1.) We present a novel definition for secure and robust outsourcing schemes and underline why this is needed in practice. Our definition is stronger than previous definitions for oblivious RAM or software protection in that it assures strong security guarantees against active attacks. Schemes meeting the definition not only assure that an attacker cannot learn the access pattern, but guarantee resilience to errors and the prevention of targeted attacks to specific locations. Unfortunately, several existing schemes cannot achieve this high level of security. For completeness, we provide a protocol based on Path ORAM that showcases that stronger security is actually achievable. 2.) We present a novel definition for auditable storage, capturing the guarantee that a successful audit implies that the current server state allows the client to retrieve his data. We develop an audit mechanism, based on secure and robust outsourcing schemes, that is similar to the construction by Cash et al. (Eurocrpyt 2013), but is universally composable and fault-tolerant. 3.) We revisit the security claim of a widely-used challenge-response audit mechanism, in which the server has to compute a hash $H(F||c)$ on the file $F$ concatenated with a uniformly random challenge $c$ chosen by the client. Being concerned with composable security, we prove that this audit mechanism is not secure, even in the random oracle model, without additional assumptions. The composable security of this basic audit scheme was implicitly assumed in Ristenpart et al. (Eurocrypt 2011). To complete the picture, we state the additional assumptions for this audit mechanism to be provably secure and investigate the (in)applicability of hash-function constructions in this setting.

Efficient Constant Round Multi-Party Computation Combining BMR and SPDZ

Tue, 12/19/2017 - 02:10
Recently, there has been huge progress in the field of concretely efficient secure computation, even while providing security in the presence of \emph{malicious adversaries}. This is especially the case in the two-party setting, where constant-round protocols exist that remain fast even over slow networks. However, in the multi-party setting, all concretely efficient fully-secure protocols, such as SPDZ, require many rounds of communication. In this paper, we present an MPC protocol that is fully-secure in the presence of malicious adversaries and for any number of corrupted parties. Our construction is based on the constant-round BMR protocol of Beaver et al., and is the first version of that protocol that is \emph{concretely} efficient for the dishonest majority case. Our protocol includes an online phase that is extremely fast and mainly consists of each party locally evaluating a garbled circuit. For the offline phase we present both a generic construction (using any underlying MPC protocol), and a highly efficient instantiation based on the SPDZ protocol. Our estimates show the protocol to be considerably more efficient than previous fully-secure multi-party protocols.

Raziel: Private and Verifiable Smart Contracts on Blockchains

Mon, 12/18/2017 - 21:39
Raziel combines secure multi-party computation and proof-carrying code to provide privacy, correctness and verifiability guarantees for smart contracts on blockchains. Effectively solving DAO and Gyges attacks, this paper describes an implementation and presents examples to demonstrate its practical viability (e.g., private and verifiable crowdfundings and investment funds). Additionally, we show how to use Zero-Knowledge Proofs of Proofs (i.e., Proof-Carrying Code certificates) to prove the validity of smart contracts to third parties before their execution without revealing anything else. Finally, we show how miners could get rewarded for generating pre-processing data for secure multi-party computation.

Probabilistic and Considerate Attestation of IoT Devices against Roving Malware

Mon, 12/18/2017 - 20:14
Remote Attestation (RA) is a popular means of detecting malware presence (or verifying its absence) on embedded and IoT devices. It is especially relevant to low-end devices that are incapable of protecting themselves against infection. Malware that is aware of ongoing or impending attestation and aims to avoid detection can relocate itself during computation of the attestation measurement. In order to thwart such behavior, prior RA techniques are either non-interruptible or explicitly forbid modification of storage during measurement computation. However, since the latter can be a time-consuming task, this curtails availability of device's other (main) functions, which is especially undesirable, or even dangerous, for devices with time- and/or safety-critical missions. In this paper, we propose SMARM, a light-weight technique, based on shuffled measurements, as a defense against roving malware. In SMARM, memory is measured in a randomized and secret order. This does not impact device's availability -- the measurement process can be interrupted, even by malware, which can relocate itself at will. We analyze various malware behaviors and show that, while malware can escape detection in a single attestation instance, it is highly unlikely to avoid eventual detection.

Lattice-Based Public Key Encryption with Keyword Search

Mon, 12/18/2017 - 18:46
Public key Encryption with Keyword Search (PEKS) aims in mitigating the impacts of data privacy versus utilization dilemma by allowing any user in the system to send encrypted files to the server to be searched by a receiver. The receiver can retrieve the encrypted files containing specific keywords by providing the corresponding trapdoors of these keywords to the server. Despite their merits, the existing PEKS schemes introduce a high end-to-end delay that may hinder their adoption in practice. Moreover, they do not scale well for large security parameters and provide no post-quantum security promise. In this paper, we propose novel lattice-based PEKS schemes that offer a high computational efficiency along with better security assurances than that of existing alternatives. Specifically, our NTRU-PEKS scheme achieves 18 times lower end-to-end delay than the most efficient pairing-based alternatives. Our LWE-PEKS offers provable security in the standard model with a reduction to the worst-case lattice problems. We fully implemented our NTRU-PEKS on embedded devices with a deployment on real cloud infrastructures to demonstrate its effectiveness.

"HILA5 Pindakaas": On the CCA security of lattice-based encryption with error correction

Mon, 12/18/2017 - 17:17
We show that HILA5 is not secure against chosen-ciphertext attacks. Specifically, we demonstrate a key-recovery attack on HILA5 using an active attack on reused keys. The attack works around the error correction in HILA5. The attack applies to the HILA5 key-encapsulation mechanism (KEM), and also to the public-key encryption mechanism (PKE) obtained by NIST's procedure for combining the KEM with authenticated encryption. This contradicts the most natural interpretation of the IND-CCA security claim for HILA5.

On hybrid SIDH schemes using Edwards and Montgomery curve arithmetic

Mon, 12/18/2017 - 17:13
Supersingular isogeny Diffie-Hellman (SIDH) is a proposal for a quantum-resistant key exchange. The state-of-the-art implementation works entirely with Montgomery curves and basically can be divided into elliptic curve arithmetic and isogeny arithmetic. It is well known that twisted Edwards curves can provide a more efficient elliptic curve arithmetic. Therefore it was hinted by Costello and Hisil, that by using only Edwards curves for isogeny and curve arithmetic, or a hybrid scheme, that uses Edwards curve arithmetic and switches between the models whenever needed, a speedup in the computation may be gained. Following the latter case, we investigated how to efficiently switch between Montgomery and twisted Edwards curves in SIDH, and how to insert Edwards arithmetic in the current state-of-the-art implementation. We did not gain a speedup compared to the results of Costello, Longa, and Naehrig, but in some cases the performance of Edwards arithmetic is almost equally fast. Thus, we suppose that a hybrid scheme does not improve the performance of SIDH, but still can be interesting for platforms having special hardware acceleration for Edwards curves. However, a full Edwards SIDH version may give a speedup, if fast Edwards isogeny formulas can be found.

A New Crypto-Classifier Service for Energy Efficiency in Smart Cities

Mon, 12/18/2017 - 17:12
Smart Cities draw a nice picture of a connected city where useful services and data are ubiquitous, energy is properly used and urban infrastructures are well orchestrated. Fulfilling this vision in our cities implies unveiling citizens data and assets. Thus, security and data privacy appear as crucial issues to consider. In this paper, we study a way of offering a secured energy management service for diagnosis and classification of buildings in a district upon their energy efficiency. Our remote service can be beneficial both for local authorities and householders without revealing private data. Our framework is designed such that the private data is permanently encrypted and that the server performing the labeling algorithm has no information about the sensitive data and no capability to decrypt it. The underlying cryptographic technology used is homomorphic encryption, allowing to perform calculations directly on encrypted data. We present here the prototype of a crypto-classification service for energy consumption profiles involving different actors of a smart city community, as well as the associated performances results. We assess our proposal atop of real data taken from an Irish residential district and we show that our service can achieve acceptable performances in terms of security, execution times and memory requirements.

Zero-Sum Partitions of PHOTON Permutations

Mon, 12/18/2017 - 17:11
We describe an approach to zero-sum partitions using Todo's division property at EUROCRYPT 2015. It follows the inside-out methodology, and includes MILP-assisted search for the forward and backward trails, and subspace approach to connect those two trails that is less restrictive than commonly done. As an application we choose PHOTON, a family of sponge-like hash function proposals that was recently standardized by ISO. With respect to the security claims made by the designers, we for the first time show zero-sum partitions for almost all of those full 12-round permutation variants that use a 4-bit S-Box. As with essentially any other zero-sum property in the literature, also here the gap between a generic attack and the shortcut is small.

Two-Face: New Public Key Multivariate Schemes

Mon, 12/18/2017 - 17:09
We present here new multivariate schemes that can be seen as HFE generalization having a property called `Two-Face'. Particularly, we present five such families of algorithms named `Dob', `Simple Pat', `General Pat', `Mac', and `Super Two-Face'. These families have connections between them, some of them are refinements or generalizations of others. Notably, some of these schemes can be used for public key encryption, and some for public key signature. We introduce also new multivariate quadratic permutations that may have interest beyond cryptography.

Improvements for Finding Impossible Differentials of Block Cipher Structures

Mon, 12/18/2017 - 17:08
In this paper we improve Wu and Wang's method for finding impossible differentials of block cipher structures. This improvement is more general than Wu and Wang's method that it can find more impossible differentials with less time. We apply it on Gen-CAST256, Misty, Gen-Skipjack, Four-Cell, Gen-MARS, SMS4, MIBS, Camellia*, LBlock, E2 and SNAKE block ciphers. All impossible differentials discovered by the algorithm are the same as Wu's method. Besides, for the 8-round MIBS block cipher, we find 4 new impossible differentials, which are not listed in Wu and Wang's results. The experiment results show that the improved algorithm can not only find more impossible differentials, but also largely reduce the search time.

Security notions for cloud storage and deduplication

Mon, 12/18/2017 - 17:07
Cloud storage is in widespread use by individuals and enterprises but introduces a wide array of attack vectors. A basic step for users is to encrypt their data, but it is not obvious what precise security properties are required for encryption. Furthermore, cloud storage providers often use techniques such as data deduplication for improving efficiency which restricts the application of semantically-secure encryption. Generic security goals and attack models have thus far proved elusive: primitives are considered in isolation and protocols are often proved secure under ad hoc models for restricted classes of adversaries. We provide a generic syntax for storage systems that allows us to formally model natural security notions for cloud storage and deduplication. We define security notions for confidentiality and integrity in encrypted cloud storage and determine relations between these notions. We show how to build cloud storage systems that satisfy our defined security notions using generic cryptographic components.

Unconditionally secure multi-party quantum commitment scheme

Mon, 12/18/2017 - 17:05
A new unconditionally secure multi-party quantum commitment is proposed in this paperby encoding the committed message to the phase of a quantum state. Multi-party means that there are more than one recipient in our scheme. We show that our quantum commitment scheme is unconditional hiding and binding, and hiding is perfect. Our technique is based on the interference of phase-encoded coherent states of light. Its security proof relies on the no-cloning theorem of quantum theory and the properties of quantum information.


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