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2015-07-01
03:17 [Pub][ePrint] Adaptive Proofs of Knowledge in the Random Oracle Model, by David Bernhard and Marc Fischlin and Bogdan Warinschi

  We formalise the notion of adaptive proofs of knowledge in the random oracle model,

where the extractor has to recover witnesses for multiple, possibly adaptively chosen

statements and proofs. We also discuss extensions to simulation soundness, as typically

required for the ``encrypt-then-prove\'\' construction of strongly secure encryption

from IND-CPA schemes.

Utilizing our model we show three results:

(1) Simulation-sound adaptive proofs exist.

(2) The ``encrypt-then-prove\'\' construction with a simulation-sound

adaptive proof yields CCA security. This appears to be a ``folklore\'\' result

but which has never been proven in the random oracle model. As a corollary, we

obtain a new class of CCA-secure encryption schemes.

(3) We show that the

Fiat-Shamir transformed Schnorr protocol is _not_ adaptively secure and

discuss the implications of this limitation.

Our result not only separates

adaptive proofs from proofs of knowledge, but also gives a strong hint why

Signed ElGamal as the most prominent encrypt-then-prove example has not been

proven CCA-secure without making further assumptions.



03:17 [Pub][ePrint] On the Hardness of Proving CCA-security of Signed ElGamal, by David Bernhard and Marc Fischlin and Bogdan Warinschi

  The well-known Signed ElGamal scheme consists of ElGamal

encryption with a non-interactive Schnorr proof of knowledge. While this

scheme should be intuitively secure against chosen-ciphertext attacks

in the random oracle model, its security has not yet been proven nor

disproven so far, without relying on further non-standard assumptions

like the generic group model. Currently, the best known positive result

is that Signed ElGamal is non-malleable under chosen-plaintext attacks.

In this paper we provide evidence that Signed ElGamal may not be CCA

secure in the random oracle model. That is, building on previous work of

Shoup and Gennaro (Eurocrypt\'98), Seurin and Treger (CT-RSA 2013),

and Bernhard et al. (PKC 2015), we exclude a large class of potential

reductions that could be used to establish CCA security of the scheme.



03:17 [Pub][ePrint] A New Encryption Standard of Ukraine: The Kalyna Block Cipher, by Roman Oliynykov and Ivan Gorbenko and Oleksandr Kazymyrov and Victor Ruzhentsev and Oleksandr Kuznetsov and Yurii Gorbenko and Oleksan

  The Kalyna block cipher was selected during Ukrainian National Public Cryptographic Competition (2007-2010) and its slight modification was approved as the new encryption standard of Ukraine in 2015. Main requirements for Kalyna were both high security level and high performance of software implementation on general-purpose 64-bit CPUs. The cipher has SPN-based (Rijndael-like) structure with increased MDS matrix size, a new set of four different S-boxes, pre- and postwhitening using modulo 2^{64} addition and a new construction of the key schedule. Kalyna supports block size and key length of 128, 256 and 512 bits (key length can be either equal or double of the block size). On the time of this paper publishing, no more effective cryptanalytic attacks than exhaustive search are known. In this paper we present the adapted English translated specification of Kalyna as it is given in the national standard of Ukraine.



03:17 [Pub][ePrint] Secure Execution Architecture based on PUF-driven Instruction Level Code Encryption, by Stephan Kleber and Florian Unterstein and Matthias Matousek and Frank Kargl and Frank Slomka and Matthias Hiller

  A persistent problem with program execution, despite numerous mitigation attempts, is its inherent vulnerability to the injection of malicious code. Equally unsolved is the susceptibility of firmware to reverse engineering, which undermines the manufacturer\'s code confidentiality. We propose an approach that solves both kinds of security problems employing instruction-level code encryption combined with the use of a physical unclonable function (PUF). Our novel Secure Execution PUF-based Processor (SEPP) architecture is designed to minimize the attack surface, as well as performance impact, and requires no significant changes to the development process. This is possible based on a tight integration of a PUF directly into the processor\'s instruction pipeline. Furthermore, cloud scenarios and distributed embedded systems alike inherently depend on remote execution; our approach supports this, as the secure execution environment needs not to be locally available at the developers site. We implemented an FPGA-based prototype based on the OpenRISC Reference Platform. To assess our results, we performed a security analysis of the processor and evaluated the performance impact of the encryption. We show that the attack surface is significantly reduced compared to previous approaches while the performance penalty is at a reasonable factor of about 1.5.



03:17 [Pub][ePrint] Modelling ciphersuite and version negotiation in the TLS protocol, by Benjamin Dowling and Douglas Stebila

  Real-world cryptographic protocols such as the widely used Transport Layer Security (TLS) protocol support many different combinations of cryptographic algorithms (called ciphersuites) and simultaneously support different versions. Recent advances in provable security have shown that most modern TLS ciphersuites are secure authenticated and confidential channel establishment (ACCE) protocols, but these analyses generally focus on single ciphersuites in isolation. In this paper we extend the ACCE model to cover protocols with many different sub-protocols, capturing both multiple ciphersuites and multiple versions, and define a security notion for secure negotiation of the optimal sub-protocol. We give a generic theorem that shows how secure negotiation follows, with some additional conditions, from the authentication property of secure ACCE protocols. Using this framework, we analyse the security of ciphersuite and three variants of version negotiation in TLS, including a recently proposed mechanism for detecting fallback attacks.





2015-06-30
21:17 [Pub][ePrint] Security Analysis of Niu et al. Authentication and Ownership Management Protocol, by Nasour Bagheri, Masoumeh Safkhani and Hoda Jannati

  Over the past decade, besides authentication, ownership

management protocols have been suggested to transfer or

delegate the ownership of RFID tagged items. Recently, Niu et

al. have proposed an authentication and ownership management

protocol based on 16-bit pseudo random number generators and

exclusive-or operations which both can be easily implemented on

low-cost RFID passive tags in EPC global Class-1 Generation-2

standard. They claim that their protocol offers location and data

privacy and also resists against desynchronization attack. In this

paper, we analyze the security of their proposed authentication

and ownership management protocol and show that the protocol

is vulnerable to secret disclosure and desynchronization attacks.

The complexity of most of the attacks are only two runs of the

protocol and the success probability of the attacks are almost 1.



21:17 [Pub][ePrint] The leaking battery A privacy analysis of the HTML5 Battery Status API, by Lukasz Olejnik and Gunes Acar and Claude Castelluccia and Claudia Diaz

  We highlight the privacy risks associated with the HTML5 Battery Status API. We put special focus on its implementation in the Firefox browser. Our study shows that websites can discover the capacity of users\' batteries by exploiting the high precision readouts provided by Firefox on Linux. The capacity of the battery, as well as its level, expose a fingerprintable surface that can be used to track web users in short time intervals. Our analysis shows that the risk is much higher for old or used batteries with reduced capacities, as the battery capacity may potentially serve as a tracking identifier. The fingerprintable surface of the API could be drastically reduced without any loss in the API\'s functionality by reducing the precision of the readings. We propose minor modifications to Battery Status API and its implementation in the Firefox browser to address the privacy issues presented in the study. Our bug report for Firefox was accepted and a fix is deployed.



21:17 [Pub][ePrint] Generalised tally-based decoders for traitor tracing and group testing, by Boris Skoric and Wouter de Groot

  We propose a new type of score function for Tardos traitor tracing codes. It is related to the recently introduced tally-based score function, but it utilizes more of the information available to the decoder. It does this by keeping track of sequences of symbols in the distributed codewords instead of looking at columns of the code matrix individually.

We derive our new class of score functions from a Neyman-Pearson hypothesis test and illustrate its performance with simulation results.

Finally we derive a score function for (medical) group testing applications.



21:17 [Pub][ePrint] An Authentication Code over Galois Rings with Optimal Impersonation and Substitution Probabilities, by Juan Carlos Ku-Cauich Guillermo Morales-Luna Horacio Tapia-Recillas

  A new systematic authentication scheme based on the Gray map

over Galois rings is introduced. The Gray map determines an isometry between

the Galois ring and a vector space over a Galois eld. The introduced code

attains optimal impersonation and substitution probabilities.



21:17 [Pub][ePrint] Construction of Arithmetic Secret Sharing Schemes by Using Torsion Limits, by Seher Tutdere and Osmanbey Uzunkol

  Recent results of Cascudo, Cramer, and Xing on the construction of arithmetic secret sharing schemes are improved by using some new bounds on the torsion limits of algebraic function fields. Furthermore, new bounds on the torsion limits of certain towers of function fields are given.



21:17 [Pub][ePrint] Statistical Concurrent Non-malleable Zero-knowledge from One-way Functions, by Susumu Kiyoshima

  Concurrent non-malleable zero-knowledge (CNMZK) protocols are zero-knowledge protocols that are secure even against adversaries that interact with multiple provers and verifiers simultaneously. Recently, the first statistical CNMZK argument for NP was constructed under the DDH assumption (Orlandi el al., TCC\'14).

In this paper, we construct a statistical CNMZK argument for NP assuming only the existence of one-way functions. The security is proven via black-box simulation, and the round complexity is poly(n). Under the existence of collision-resistant hash functions, the round complexity can be reduced to w(log n), which is known to be essentially optimal for black-box concurrent zero-knowledge protocols.