International Association for Cryptologic Research

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2014-09-20
00:17 [Pub][ePrint]

We give a detailed account of the use of \$$\\mathbb{Q}\$$-curve reductions to construct elliptic curves over \$$\\mathbb{F}_{p^2}\$$ with efficiently computable endomorphisms, which can be used to accelerate elliptic curve-based cryptosystems in the same way as Gallant--Lambert--Vanstone (GLV) and Galbraith--Lin--Scott (GLS) endomorphisms.

Like GLS (which is a degenerate case of our construction), we offer the advantage over GLV of selecting from a much wider range of curves, and thus finding secure group orders when \$$p\$$ is fixed for efficient implementation.

Unlike GLS, we also offer the possibility of constructing twist-secure curves.

We construct several one-parameter families of elliptic curves over \$$\\mathbb{F}_{p^2}\$$ equipped with efficient endomorphisms for every \$$p > 3\$$, and exhibit examples of twist-secure curves over \$$\\mathbb{F}_{p^2}\$$ for the efficient Mersenne prime \$$p = 2^{127}-1\$$.

00:17 [Pub][ePrint]

The Protocol for Lightweight Authentication of Identity (PLAID) aims at secure and private authentication between a smart card and a terminal. Originally developed by a unit of the Australian Department of Human Services for physical and logical access control, PLAID has now been standardized as an Australian standard AS-5185-2010 and is currently in the fast track standardization process for ISO/IEC 25182-1.2. We present a cryptographic evaluation of PLAID. As well as reporting a number of undesirable cryptographic features of the protocol, we show that the privacy properties of PLAID are significantly weaker than claimed: using a variety of techniques we can fingerprint and then later identify cards. These techniques involve a novel application of standard statistical and data analysis techniques in cryptography. We also discuss countermeasures to our attacks.

00:17 [Pub][ePrint]

This paper shows how to securely authenticate messages using just 29 bit operations per authenticated bit, plus a constant overhead per message. The authenticator is a standard type of \"universal\" hash function providing information-theoretic security; what is new is computing this type of hash function at very high speed.

At a lower level, this paper shows how to multiply two elements of a field of size 2^128 using just 9062 \\approx 71 * 128 bit operations, and how to multiply two elements of a field of size 2^256 using just 22164 \\approx 87 * 256 bit operations. This performance relies on a new representation of field elements and new FFT-based multiplication techniques.

This paper\'s constant-time software uses just 1.89 Core 2 cycles per byte to authenticate very long messages. On a Sandy Bridge it takes 1.43 cycles per byte, without using Intel\'s PCLMULQDQ polynomial-multiplication hardware. This is much faster than the speed records for constant-time implementations of GHASH without PCLMULQDQ (over 10 cycles/byte), even faster than Intel\'s best Sandy Bridge implementation of GHASH with PCLMULQDQ (1.79 cycles/byte), and almost as fast as state-of-the-art 128-bit prime-field MACs using Intel\'s integer-multiplication hardware (around 1 cycle/byte).

00:17 [Pub][ePrint]

The focus of this paper is on differential privacy of streaming data using sketch-based algorithms. Previous works, like Dwork {\\it et al.} (ICS 2010, STOC 2010), explored random sampling based streaming algorithms. We work in the well studied streaming model of computation, where the database is stored in the form of a matrix and a curator can access the database row-wise or column-wise.

Dwork {\\it et al.} (STOC 2010) gave impossibility result for any non-trivial query on a streamed data with respect to the user level privacy. Therefore, in this paper, we restrict our attention to the event level privacy. {We provide optimal, up to logarithmic factor, space differentially private mechanism in the streaming model for three basic linear algebraic tasks: matrix multiplication, linear regression, and low rank approximation, while incurring significantly less additive error}.

Our approach for matrix multiplication and linear regression has some similarities with Blocki {\\it et al.} (FOCS 2012) and Upadhyay (ASIACRYPT 2013) on the superficial level, but there are some subtle differences. For example, they perform an affine transformation to convert the private matrix in to a set of $\\{\\sqrt{w/n},1\\}^n$ vectors for some appropriate $w$, while we perform an input perturbation that raises the singular value of the private matrix. %On a high level, the mechanism for linear regression and matrix multiplication can be seen as a private analogue of the known streaming algorithms. In order to get a streaming algorithm for low rank approximation, we have to reuse the random Gaussian matrix in a specific way. We prove that the resulting distribution also preserve differential privacy.

We do not make any assumptions, like singular value separation, as made in the earlier works of Hardt and Roth (STOC 2013) and Kapralov and Talwar (SODA 2013). Further, we do not assume normalized row as in the work of Dwork {\\it et al.} (STOC 2014). All our mechanisms, in the form presented, can also be computed in the distributed setting of Biemel, Nissim, and Omri (CRYPTO 2008).

00:17 [Pub][ePrint]

Secure protocols for password-based user authentication are well-studied in the cryptographic literature but have failed to see wide-spread adoption on the Internet; most proposals to date require extensive modifications to the Transport Layer Security (TLS) protocol, making deployment challenging. Recently, a few modular designs have been proposed in which a cryptographically secure password-based mutual authentication protocol is run inside a confidential (but not necessarily authenticated) channel such as TLS; the password protocol is bound to the established channel to prevent active attacks. Such protocols are useful in practice for a variety of reasons: security no longer relies on users\' ability to validate server certificates and can potentially be implemented with no modifications to the secure channel protocol library.

We provide a systematic study of such authentication protocols. Building on recent advances in modelling TLS, we give a formal definition of the intended security goal, which we call password-authenticated and confidential channel establishment (PACCE). We show generically that combining a secure channel protocol, such as TLS, with a password authentication protocol, where the two protocols are bound together using either the transcript of the secure channel\'s handshake or the server\'s certificate, results in a secure PACCE protocol. Our prototype based on TLS is available as a cross-platform client-side Firefox browser extension and a server-side web application which can easily be installed on deployed web browsers and servers.

00:17 [Pub][ePrint]

Although newly proposed, tree-based Oblivious RAM schemes are drastically more efficient than older techniques, they come with a significant drawback: an inherent dependence on a fixed-size database. This capability is vital for real-world use of Oblivious RAM since one of its most promising deployment scenarios is for cloud storage, where scalability and elasticity are crucial. We revisit the original construction by Shi et al. [16] and propose several ways to support both increasing and decreasing the ORAM\'s size with sublinear communication. We show that increasing capacity can be accomplished by adding leaf nodes to the tree, but that it must be done carefully in order to preserve the probabilistic integrity of the data structures. We also provide new, tighter bounds for the size of interior and leaf nodes in the scheme, saving bandwidth and storage over previous constructions. Finally, we define an oblivious pruning technique for removing leaf nodes and decreasing the size of the tree. We show that this pruning method is both secure and efficient.

00:17 [Pub][ePrint]

The Learning with Errors (LWE) problem has gained a lot of attention in recent years leading to a series of new cryptographic applications. Specifically, it states that it is hard to distinguish random linear equations disguised by some small error from truly random ones. Interestingly, cryptographic primitives based on LWE often do not exploit the full potential of the error term beside of its importance for security.

To this end, we introduce a novel LWE-close assumption, namely Augmented Learning with Errors (A-LWE), which allows to hide auxiliary data injected into the error term by a technique that we call message embedding. In particular, it enables existing cryptosystems to strongly increase the message throughput per ciphertext. We show that A-LWE is for certain instantiations at least as hard as the LWE problem. This inherently leads to new cryptographic constructions providing high data load encryption and customized security properties as required, for instance, in economic environments such as stock markets resp. for financial transactions. The security of those constructions basically stems from the hardness to solve the A-LWE problem.

As an application we introduce (among others) the first lattice-based replayable chosen-ciphertext secure encryption scheme from A-LWE.

00:17 [Pub][ePrint]

In the last few years, several practitioners have proposed a

wide range of approaches for reducing the implementation area of the

AES in hardware. However, an area-throughput trade-off that undermines high-speed is not realistic for real-time cryptographic applications. In this manuscript, we explore how Genetic Algorithms (GAs) can be used for pipelining the AES substitution box based on composite field arithmetic. We implemented a framework that parses and analyzes a Verilog netlist, abstracts it as a graph of interconnected cells and generates circuit statistics on its elements and paths. With this information, the GA extracts the appropriate arrangement of Flip-Flops (FFs) that maximizes the throughput of the given netlist. In doing so, we show that it is possible to achieve a 50 % improvement in throughput with only an 18 % increase in area in the UMC 0.13 um low-leakage standard cell library.

00:17 [Pub][ePrint]

Verifiable Secret Sharing (VSS) guarantees that honest parties reconstruct a consistent secret even in the presence of a malicious dealer that distributes invalid shares. We empower the dishonest dealer and consider the case when he subliminally leaks information in valid shares, allowing an adversary to access the secret prior to the reconstruction phase. We define the concept of Dealer-Leakage Resilient Verifiable Secret Sharing (DLR-VSS) as a stronger notion of VSS that achieves security under this settings. We propose an efficient DLR-VSS and prove its properties in the semi-honest adversarial model.

00:17 [Pub][ePrint]

In this paper, we comprehensively study the resistance of keyed variants of SHA-3 (Keccak) against algebraic attacks. This analysis covers a wide range of key recovery, MAC forgery and other types of attacks, breaking up to 9 rounds (out of the full 24) of the Keccak internal permutation much faster than exhaustive search. Moreover, some of our attacks on the 6-round Keccak are completely practical and were verified on a desktop PC. Our methods combine cube attacks (an algebraic key recovery attack) and related algebraic techniques with structural analysis of the Keccak permutation. These techniques should be useful in future cryptanalysis of Keccak and similar designs.

Although our attacks break more rounds than previously published techniques, the security margin of Keccak remains large. For Keyak -- a Keccak-based authenticated encryption scheme -- the nominal number of rounds is 12 and therefore its security margin is smaller (although still sufficient).

2014-09-17
21:17 [Pub][ePrint]

Compression is desirable for network applications as it saves bandwidth; however, when data is compressed before being encrypted, the amount of compression leaks information about the amount of redundancy in the plaintext. This side channel has led to successful real-world attacks (the CRIME and BREACH attacks) on web traffic protected by the Transport Layer Security (TLS) protocol. The general guidance in light of these attacks has been to disable compression, preserving confidentiality but sacrificing bandwidth. In this paper, we examine two techniques---heuristic separation of secrets and fixed-dictionary compression---for enabling compression while protecting high-value secrets, such as cookies, from attack. We model the security offered by these techniques and report on the amount of compressibility that they can achieve.