International Association for Cryptologic Research

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2015-07-18
15:17 [Pub][ePrint]

This paper offers a new version of the hHB protocol denoted Light-hHB. This proposal uses the same framework as hHB, that is a two stages protocol: the first one for the establishment of a session key between the reader and the tag and the second one similar to HB+. We also introduce in this paper a novel and lightweight key exchange protocol inspired by the BB84 protocol named the non-quantum key exchange protocol. With the use of a practical implementation of the latter protocol in the first stage of Light-hHB, the transmission cost is drastically reduced compared to the one of hHB, which is its main drawback. In the context of RFID tags, Light-hHB is significantly more practical than hHB and achieves the same security goals.

15:17 [Pub][ePrint]

In this paper, we first present a new class of code based public key cryptosystem(PKC) based on Reed-Solomon code over $\\mathbb{F}_{2^m}$, referred to as K(XVI)SE(1)PKC.

We then present a new class of quadratic multivariate PKC, K(XVI)SE(2)PKC, based on cyclic code over $\\mathbb{F}_2$.

We show that both K(XVI)SE(1)PKC and K(XVI)SE(2)PKC can be secure against the various linear transformation attacks such as Gr\\\"obner bases attack due to a non-linear structure introduced to the ciphertexts.

Namely, thanks to the non-linear transformation introduced in the construction of K(XVI)SE(1)PKC and K(XVI)SE(2)PKC the ciphertexts can be made very secure against the various sorts of linear transformation attacks such as Gr\\\"obner bases attack, although the degree of the multivariate polynomial is all degree 1.

A new scheme presented in this paper that transforms message variables in order to realize non-linear transformations, K(I)TS, would yield a brand-new technique in the field of both code based PKC and multivariate PKC, for much improving the security.

We shall show that the K(XVI)SE(1)PKC can be effectively constructed based on the Reed-Solomon code over $\\mathbb{F}_{2^8}$, extensively used in the present day storage systems

or the various digital transmission systems.

15:17 [Pub][ePrint]

We investigate new constructions of n-circular counterexamples with a focus on the case of n=2. We have a particular interest in what qualities a cryptosystem must have to be able to separate such circular security from IND-CPA or IND-CCA security. To start, we ask whether there is something special about the asymmetry in bilinear groups that is inherent in the works of ABBC10 and CGH12 or whether it is actually the bilinearity that matters. As a further question, we explore whether such counterexamples are derivable from other

assumptions such as the Learning with Errors (LWE) problem. If it were difficult to find such counterexamples, this might bolster are confidence in using 2-circular encryption as a method of bootstrapping Fully Homomorphic Encryption systems that are based on lattice assumptions.

The results of this paper broadly expand the class of assumptions under which we can build 2-circular counterexamples. We first show for any constant k >= 2 how to build counterexamples from a bilinear group under the decision k-linear assumption. Recall that the decision k-linear assumption becomes progressively weaker as k becomes larger. This means that we can instantiate counterexamples

from symmetric bilinear groups and shows that asymmetric groups do not have any inherently special property needed for this problem.

We then show how to create 2-circular counterexamples from the Learning with Errors problem. This extends the reach of these systems beyond bilinear groups and obfuscation.

2015-07-16
18:11 [Pub][ePrint]

We present here optimized implementations of the MAKWA password hashing

function on an AMD Radeon HD 7990 GPU, and compare its efficiency with an Intel

i7 4770K CPU for systematic dictionary attacks. We find that the GPU seems to

get more hashing done for a given budget, but not by a large amount (the GPU is less

than twice as efficient as the CPU). Raising the MAKWA modulus size to 4096 bits,

instead of the default 2048 bits, should restore the balance in favour of the CPU. We

also find that power consumption, not hardware retail price, is likely to become the

dominant factor for industrialized, long-term attacking efforts.

18:11 [Pub][ePrint]

Statistical analysis of attacks on symmetric ciphers often require assuming the normal behaviour of a test statistic.

Typically such an assumption is made in an asymptotic sense. In this work, we consider concrete versions of some important

normal approximations that have been made in the literature. To do this, we use the Berry-Ess\\\'{e}en theorem to derive

explicit bounds on the approximation errors. Analysing these error bounds in the cryptanalytic context throws up several

surprising results. One important implication is that this puts in doubt the applicability of the order statistics

based approach for analysing key recovery attacks on block ciphers. This approach has been earlier used to obtain several

results on the data complexities of (multiple) linear and differential cryptanalysis. The non-applicability of the order

statistics based approach puts a question mark on the data complexities obtained using this approach. Fortunately, we

are able to recover all of these results by utilising the hypothesis testing framework. Detailed consideration of the

error in normal approximation also has implications for $\\chi^2$ and the log-likelihood ratio (LLR) based test statistics.

The normal approximation of the $\\chi^2$ test statistics has some serious and counter-intuitive restrictions. One such

restriction is that for multiple linear cryptanalysis as the number of linear approximations grows so does the requirement

on the number of plaintext-ciphertext pairs for the approximation to be proper. The issue of satisfactorily addressing the

problems with the application of the $\\chi^2$ test statistics remains open. For the LLR test statistics, previous work

used a normal approximation followed by another approximation to simplify the parameters of the normal approximation. We

derive the error bound for the normal approximation which turns out to be difficult to interpret. We show that the approximation

required for simplifying the parameters restricts the applicability of the result. Further, we argue that this approximation

is actually not required. More generally, the message of our work is that all cryptanalytic attacks should properly derive and

interpret the error bounds for any normal approximation that is made.

18:11 [Pub][ePrint]

We show the first positive results for the indifferentiability security of the confusion-diffusion networks (which are extensively used in the design of block ciphers and hash functions). In particular, our result shows that a constant number of confusion-diffusion rounds is sufficient to extend the domain of a public random permutation.

18:11 [Pub][ePrint]

A secure ad-hoc survey scheme enables a survey authority to independently (without any interaction) select an ad-hoc group of registered users based only on their identities (e.g., their email addresses), and create a survey where only selected users can anonymously submit exactly one response.

We present a formalization of secure ad-hoc surveys and present:

* an abstract provably-secure implementation based on standard cryptographic building blocks (which in particular are implied by the existence of enhanced trapdoor permutations in the CRS model);

* a practical instantiation of our abstract protocol, called ANONIZE, which is provably-secure in the random oracle model based on cryptographic assumptions on groups with bilinear maps.

As far as we know, ANONIZE constitutes the first implementation of a large-scale secure computation protocol (of non-trivial functionalities) that can scale to millions of users.

18:11 [Pub][ePrint]

MISTY1 is a block cipher designed by Matsui in 1997. It was well evaluated and standardized by projects, such as CRYPTREC, ISO/IEC, and NESSIE. In this paper, we propose a key recovery attack on the full MISTY1, i.e., we show that 8-round MISTY1 with 5 FL layers does not have 128-bit security. Many attacks against MISTY1 have been proposed, but there is no attack against the full MISTY1. Therefore, our attack is the first cryptanalysis against the full MISTY1. We construct a new integral characteristic by using the propagation characteristic of the division property, which was proposed in 2015. We first improve the division property by optimizing a public S-box and then construct a 6-round integral characteristic on MISTY1. Finally, we recover the secret key of the full MISTY1 with $2^{63.58}$ chosen plaintexts and $2^{121}$ time complexity. Moreover, if we can use $2^{63.994}$ chosen plaintexts, the time complexity for our attack is reduced to $2^{107.9}$. Note that our cryptanalysis is a theoretical attack. Therefore, the practical use of MISTY1 will not be affected by our attack.

18:11 [Pub][ePrint]

Following the line of work presented recently by Bellare, Paterson and Rogaway, we formalize and investigate the resistance of linear secret-sharing schemes to mass surveillance. This primitive is widely used to design IT systems in the modern computer world, and often it is implemented by a proprietary code that the provider (\"big brother\") could manipulate to covertly violate the privacy of the users (by implementing Algorithm-Substitution Attacks or ASAs). First, we formalize the security notion that expresses the goal of big brother and prove that for any linear secret-sharing scheme there exists an undetectable subversion of it that efficiently allows surveillance. Second, we formalize the security notion that assures that a sharing scheme is secure against ASAs and construct the first sharing scheme that meets this notion. This work could serve as an important building block towards constructing systems secure against mass surveillance.

18:11 [Pub][ePrint]

We present the first information-theoretic steganographic protocol with an asymptotically optimal ratio of key length to message length that operates on arbitrary covertext distributions with constant min-entropy. Our results are also applicable to the computational setting: our stegosystem can be composed over a pseudorandom generator to send longer messages in a computationally secure fashion. In this respect our scheme offers a significant improvement in terms of the number of pseudorandom bits generated by the two parties in comparison to previous results known in the computational setting. Central to our approach for improving the overhead for general distributions is the use of combinatorial constructions that have been found to be useful in other contexts for derandomization: almost $t$-wise independent function families.

18:11 [Pub][ePrint]

For $q$ a prime power, the discrete logarithm problem (DLP) in $\\mathbb{F}_{q}^{\\times}$ consists in finding, for any $g \\in \\mathbb{F}_{q}^{\\times}$ and $h \\in \\langle g \\rangle$, an integer $x$ such that $g^x = h$. For each prime $p$ we exhibit infinitely many extension fields $\\mathbb{F}_{p^n}$ for which the DLP in $\\mathbb{F}_{p^n}^{\\times}$ can be solved in expected quasi-polynomial time.