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21:17 [Pub][ePrint] A Second Look at Fischlin\'s Transformation, by Özgür Dagdelen and Daniele Venturi

  Fischlin\'s transformation is an alternative to the standard Fiat-Shamir transform to turn a certain class of public key identification schemes into digital signatures (in the random oracle model).

We show that signatures obtained via Fischlin\'s transformation are existentially unforgeable even in case the adversary is allowed to get arbitrary (yet bounded) information on the entire state of the signer (including the signing key and the random coins used to generate signatures). A similar fact was already known for the Fiat-Shamir transform, however, Fischlin\'s transformation allows for a significantly higher leakage parameter than Fiat-Shamir.

Moreover, in contrast to signatures obtained via Fiat-Shamir, signatures obtained via Fischlin enjoy a tight reduction to the underlying hard problem. We use this observation to show (via simulations) that Fischlin\'s transformation, usually considered less efficient, outperforms the Fiat-Shamir transform in verification time for a reasonable choice of parameters. In terms of signing Fiat-Shamir is faster for equal signature sizes. Nonetheless, our experiments show that the signing time of Fischlin\'s transformation becomes, e.g., 22% of the one via Fiat-Shamir if one allows the signature size to be doubled.

21:17 [Pub][ePrint] Practical Receipt-Free Sealed-Bid Auction in the Coercive Environment, by Jaydeep Howlader, Sanjit Kumar Roy, Ashis Kumar Mal

  Sealed-Bid auction is an efficient and rational method to

establish the price in open market. However sealed-bid auctions are sub-

ject to bid-rigging attack. Receipt-free mechanisms were proposed to

prevent bid-rigging. The prior receipt-free mechanisms are based on two

assumptions; firstly, existence of untappable channel between bidders

and auction authorities. Secondly, mechanisms assume the authorities

to be honest (not colluding). Moreover the bandwidth required to com-

municate the receipt-free bids is huge. This paper presents a sealed-bid

auction mechanism to resist bid-rigging. The proposed method does not

assume untappable channel nor consider the authorities to be necessarily

honest. The proposed mechanism also manages the bandwidth efficiently,

and improves the performance of the system.

21:17 [Pub][ePrint] The Temperature Side Channel and Heating Fault Attacks, by Michael Hutter and Jörn-Marc Schmidt

  In this paper, we present practical results of data leakages of CMOS devices via the temperature side channel---a side channel that has been widely cited in literature but not well characterized yet. We investigate the leakage of processed data by passively measuring the dissipated heat of the devices. The temperature leakage is thereby linearly correlated with the power leakage model but is limited by the physical properties of thermal conductivity and capacitance. We further present heating faults by operating the devices beyond their specified temperature ratings. The efficiency of this kind of attack is shown by a practical attack on an RSA implementation. Finally, we introduce data remanence attacks on AVR microcontrollers that exploit the Negative Bias Temperature Instability (NBTI) property of internal SRAM cells. We show how to recover parts of the internal memory and present first results on an ATmega162. The work encourages the awareness of temperature-based attacks that are known for years now but not well described in literature. It also serves as a starting point for further research investigations.

21:17 [Pub][ePrint] Side-Channel Analysis on Blinded Regular Scalar Multiplications, by Benoit Feix and Mylène Roussellet and Alexandre Venelli

  We present a new side-channel attack path threatening state-of-the-art protected implementations of elliptic curves embedded scalar multiplications. Regular algorithms such as the double-and-add-always and the Montgomery ladder are commonly used to protect the scalar multiplication from simple side-channel analysis. Combining such algorithms with scalar and/or point blinding countermeasures lead to scalar multiplications protected from all known attacks. Scalar randomization, which consists in adding a random multiple of the group order to the scalar value, is a popular countermeasure due to its efficiency. Amongst the several curves defined for usage in elliptic curves products, the most used are those standardized by the NIST. The modulus, hence the orders, of these curves are sparse, primarily for efficiency reasons. In this paper, we take advantage of this specificity to present new attack paths and recover the secret scalar of state-of-the-art protected elliptic curve implementations.

21:17 [Pub][ePrint] Two-sources Randomness Extractors for Elliptic Curves, by Abdoul Aziz Ciss

  This paper studies the task of two-sources randomness extractors for elliptic curves defined over finite fields $K$, where $K$ can be a prime or a binary field. In fact, we introduce new constructions of functions over elliptic curves which take in input two random points from two differents subgroups. In other words, for a ginven elliptic curve $E$ defined over a finite field $\\mathbb{F}_q$ and two random points $P \\in \\mathcal{P}$ and $Q\\in \\mathcal{Q}$, where $\\mathcal{P}$ and $\\mathcal{Q}$ are two subgroups of $E(\\mathbb{F}_q)$, our function extracts the least significant bits of the abscissa of the point $P\\oplus Q$ when $q$ is a large prime, and the $k$-first $\\mathbb{F}_p$ coefficients of the asbcissa of the point $P\\oplus Q$ when $q = p^n$, where $p$ is a prime greater than $5$. We show that the extracted bits are close to uniform.

Our construction extends some interesting randomness extractors for elliptic curves, namely those defined in \\cite{op} and \\cite{ciss1,ciss2}, when $\\mathcal{P} = \\mathcal{Q}$. The proposed constructions can be used in any cryptographic schemes which require extraction of random bits from two sources over elliptic curves, namely in key exchange protole, design of strong pseudo-random number generators, etc.

15:17 [Pub][ePrint] FFT-Based Key Recovery for the Integral Attack, by Yosuke Todo

  The integral attack is one of the most powerful attack against block ciphers. In this paper, we propose two new techniques for the integral attack, the FFT technique and the key concealment technique. The FFT technique is useful for the integral attack with enormous chosen plaintexts. As the previous result using FFT, Collard et al. showed a new technique which reduces the complexity for the linear attack. In this paper, we review the result of Collard et al. to estimate the complexity in detail, and we show the complexity can be estimated from the number of times using the addition of integers. Moreover, we show that attacks using FFT can be applied to the integral attack. As applications, we show integral attacks against AES and CLEFIA. For AES, we show that 6-round AES can be attacked with about $2^{51.7} additions. For CLEFIA, we show that 12-round CLEFIA can be attacked with about $2^{86.9}$ additions.

15:17 [Pub][ePrint] AES-Based Authenticated Encryption Modes in Parallel High-Performance Software, by Andrey Bogdanov and Martin M. Lauridsen and Elmar Tischhauser

  Authenticated encryption (AE) has recently gained renewed interest due to the ongoing CAESAR competition. This paper deals with the performance of block cipher modes of operation for AE in parallel software. We consider the example of the AES on Intel\'s new Haswell microarchitecture that has improved intructions for AES rounds and finite field multiplication.

As opposed to most previous high-performance software implementations of operation modes -- that have considered the encryption of single messages -- we propose to process multiple messages in parallel. We demonstrate that this message scheduling is of significant advantage for most modes. As a baseline for longer messages, the performance of AES-CBC encryption on a single core increases by factor 6.8 when adopting this approach.

For the first time, we report optimized AES-NI implementations of the novel AE modes OTR, McOE-G, COBRA, and POET -- both with single and multiple messages. For almost all AE modes considered, we obtain a consistent speed-up when processing multiple messages in parallel. Notably, among the nonce-based modes, AES-CCM gets by factor 3.5 faster and its performance is about 1.2 cpb which is close to that of AES-GCM (the latter, however, possessing classes of weak keys), with AES-OCB3 still performing at only 0.69 cpb. Among the nonce-misuse resistant modes, AES-McOE-G receives a speed-up by factor 4 and its performance is about 1.44 cpb, which is faster than AES-COBRA with its 1.55 cpb but slower than AES-COPA with 1.29 cpb.

07:04 [Job][New] Ph.D. student in Quantum Cryptography, University of and CWI Amsterdam, the Netherlands, Europe

  The Institute for Logic, Language & Computation (ILLC) at the University of Amsterdam, and the Centrum Wiskunde & Informatica (CWI) are looking for a PhD candidate in the area of quantum cryptography under the supervision of Dr. Christian Schaffner.

The aim of the PhD project is to develop new quantum-cryptographic protocols (beyond the task of key distribution) and explore their possibilities and limitations. An example of an active research topic is position-based quantum cryptography. Another aspect is to investigate the security of classical cryptographic schemes against quantum adversaries (post-quantum cryptography).

Full-time appointment is on a temporary basis for a period of four years. For the first two years the PhD candidate will be appointed at the ILLC, University of Amsterdam, initially for a period of 18 months and then, on positive evaluation, for a further six months. During the final two years, the PhD candidate will be employed by the Centrum Wiskunde and Informatica (CWI). On the basis of a full-time appointment (38 hours per week), the gross monthly salary amounts to €2,083 during the first year, rising to €2,664 during the fourth year.


  • A Master\\\'s degree with excellent grades in computer science, mathematics or physics with outstanding results or a comparable degree;

  • candidates with a strong background in cryptography or quantum information processing are preferred;

  • good academic writing and presentation skills;

  • good social and organisational skills.

Preferred starting date is 1 September 2014 (or earlier if possible).

21:17 [Pub][ePrint] Proving the TLS Handshake Secure (as it is), by Karthikeyan Bhargavan and Cédric Fournet and Markulf Kohlweiss and Alfredo Pironti and Pierre-Yves Strub and Santiago Zanella-Béguelin

  The TLS protocol features a mixed bag of cryptographic algorithms and constructions, letting clients and servers negotiate their use for each run of the handshake. Although many ciphersuites are now well-understood in isolation, their composition remains problematic, and yet it is critical to obtain practical security guarantees for TLS. We experimentally confirm that all mainstream implementations of TLS share key materials between many different algorithms, some of them of dubious strength. We outline new attacks we found in their handling of session resumption and renegotiation, stressing the need to model multiple related instances of the handshake.

We systematically study the provable security of the TLS handshake, as

it is implemented and deployed. To capture the details of the standard and its main extensions, we rely on miTLS, a verified reference implementation of the protocol. miTLS inter-operates with mainstream browsers and servers for many protocol versions, configurations, and ciphersuites; and it provides application-level, provable security for some.

We propose new agile security definitions and assumptions for the signatures, key encapsulation mechanisms, and key derivation algorithms used by the TLS handshake. By necessity, our definitions are stronger than those expected with simple modern protocols.

To validate our model of key encapsulation, we prove that RSA

ciphersuites satisfy the security assumption needed for our proof of

the handshake. Specifically, we formalize the use of PKCS#1v1.5 encryption in TLS, including recommended countermeasures against Bleichenbacher attacks, and build a 3,000-line EasyCrypt proof of its security against replayable chosen-ciphertext attacks under the assumption that ciphertexts are hard to re-randomize.

Based on our new agile definitions, we construct a modular proof of security for the miTLS reference implementation of the handshake, including ciphersuite negotiation, key exchange, renegotiation, and resumption, treated as a detailed 3,600-line executable model.

We present our main definitions, constructions, and proofs for an abstract model of the protocol, featuring series of related runs of the handshake with different ciphersuites. We also describe its refinement to account for the whole reference implementation, based on automated verification tools.

21:17 [Pub][ePrint] Impact of ANSI X9.24-1:2009 Key Check Value on ISO/IEC 9797-1:2011 MACs, by Tetsu Iwata and Lei Wang

  ANSI X9.24-1:2009 specifies the key check value, which is used to verify the integrity of the blockcipher key. This value is defined as the most significant bits of the ciphertext of the zero block, and is assumed to be publicly known data for verification. ISO/IEC 9797-1:2011 illustrates a total of ten CBC MACs, where one of these MACs, the basic CBC MAC, is widely known to be insecure. In this paper, we consider the remaining nine CBC MACs and derive the quantitative security impact of using the key check value. We first show attacks against five MACs by taking advantage of the knowledge of the key check value. We then prove that the analysis is tight, in a concrete security paradigm. For the remaining four MACs, we prove that the standard birthday bound still holds even with the presence of the key check value. As a result, we obtain a complete characterization of the impact of using ANSI X9.24-1 key check value with the ISO/IEC 9797-1 MACs.

21:17 [Pub][ePrint] SETUP in Secret Sharing Schemes, by Ruxandra F. Olimid

  Secret sharing schemes split a secret into multiple shares that are usually distributed to distinct participants with the goal that only authorized subsets of participants can recover it. We show that SETUP (Secretly Embedded Trapdoor with Universal Protection) attack can be embedded in schemes that employ enough randomness to give the attacker an overwhelming advantage to access the secret. In case of ideal schemes, a coalition of a few participants (within at least one is the attacker) can succeed the attack, while in case of non-ideal schemes the attacker knowledge can be enough to reveal the secret. We exemplify the proposed attack against Shamir\'s threshold scheme, as being the most well-known and used secret sharing scheme. Finally, we consider some prevention techniques against the attack.