International Association for Cryptologic Research

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2014-03-12
21:17 [Pub][ePrint]

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]

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.

2014-03-11
15:17 [Pub][ePrint]

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.

2014-03-10
15:17 [Pub][ePrint]

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]

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.

Requirements:

• 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).

2014-03-09
21:17 [Pub][ePrint]

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]

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]

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.

21:17 [Pub][ePrint]

We are among the first to systematically investigate (memory-trace) oblivious data structures. We propose a framework for constructing a variety of oblivious data structures, achieving asymptotic performance gains in comparison with generic Oblivious RAM (ORAM). We evaluate the performance of our oblivious data structures in terms of their bandwidth over- heads, and also when applied to a secure computation setting. Finally, we leverage our new framework to design an efficient oblivious memory allocator which is particularly useful due to the community\'s recent efforts in compiling programs targeting ORAM-capable secure processors.

2014-03-07
12:42 [Event][New]

Submission: 20 June 2014