International Association
for Cryptologic Research

In ideal-lattice cryptography, lattices are generated by defining a bijective map between an ideal of a ring of integers and a subset of $\mathbb{C}^n$. This map can be taken to be the coefficient embedding and, along with the Ring-LWE problem, the canonical embedding. However, some lattices cannot be generated using the canonical embedding in a straightforward manner. In this paper, we introduce a new class of problems called $\alpha$-Ring-LWE, which combines Ring-LWE with the twisted canonical embedding. In this context, $\alpha$ stands to be a number field element that distorts the canonical embedding coordinates. We prove the hardness of $\alpha$-Ring-LWE by providing a reduction between the Ring-LWE problem to $\alpha$-Ring-LWE for both search and decision variants. As a result, we obtain a hardness result based on a hard problem over ideal lattices. The addition of a torsion factor enables the construction of a broader class of lattices as rotated lattices. An example is the construction of the integer lattice $\mathbb{Z}^n$ by embedding the ring of integers of the totally real subfield of a cyclotomic number field $\mathbb{Q}(\zeta_p)$ with $p$ being a prime number [BFOV04].

In this paper, we extend the applicability of differential fault attacks to lattice-based cryptography. We show how two deterministic lattice-based signature schemes, Dilithium and qTESLA, are vulnerable to such attacks. In particular, we demonstrate that single random faults can result in a nonce-reuse scenario which allows key recovery. We also expand this to fault-induced partial nonce-reuse attacks, which do not corrupt the validity of the computed signatures and thus are harder to detect.

Using linear algebra and lattice-basis reduction techniques, an attacker can extract one of the secret key elements after a successful fault injection. Some other parts of the key cannot be recovered, but we show that a tweaked signature algorithm can still successfully sign any message. We provide experimental verification of our attacks by performing clock glitching on an ARM Cortex-M4 microcontroller. In particular, we show that up to 65.2% of the execution time of Dilithium is vulnerable to an unprofiled attack, where a random fault is injected anywhere during the signing procedure and still leads to a successful key-recovery.

Software ever-increasingly relies on building blocks implemented by security libraries, which provide access to evolving standards, protocols, and cryptographic primitives. These libraries are often subject to complex development models and long decision-making processes, which limit the ability of contributors to participate in the development process, hinder the deployment of scientific results and pose challenges for OS maintainers.

In this paper, focusing on OpenSSL as a de-facto standard, we analyze these limits, their impact on the security of modern systems, and their significance for researchers.

We propose the OpenSSL ENGINE API as a tool in a framework to overcome these limits, describing how it fits in the OpenSSL architecture, its features, and a technical review of its internals.

We evaluate our methodology by instantiating libsuola, a new ENGINE providing support for emerging cryptographic standards such as X25519 and Ed25519 for currently deployed versions of OpenSSL, performing benchmarks to demonstrate the viability and benefits.

The results confirm that the ENGINE API offers (1) an ideal architecture to address wide-ranging security concerns; (2) a valuable tool to enhance future research by easing testing and facilitating the dissemination of novel results in real-world systems; and (3) a means to bridge the gaps between research results and currently deployed systems.

The recent line of study on randomness extractors has been a great success, resulting in exciting new techniques, new connections, and breakthroughs to long standing open problems in several seemingly different topics. These include seeded non-malleable extractors, privacy amplification protocols with an active adversary, independent source extractors (and explicit Ramsey graphs), and non-malleable codes in the split state model. Previously, the best constructions are given in [Li17]: seeded non-malleable extractors with seed length and entropy requirement $O(\log n+\log(1/\epsilon)\log \log (1/\epsilon))$ for error $\epsilon$; two-round privacy amplification protocols with optimal entropy loss for security parameter up to $\Omega(k/\log k)$, where $k$ is the entropy of the shared weak source; two-source extractors for entropy $O(\log n \log \log n)$; and non-malleable codes in the $2$-split state model with rate $\Omega(1/\log n)$. However, in all cases there is still a gap to optimum and the motivation to close this gap remains strong.

In this paper, we introduce a set of new techniques to further push the frontier in the above questions. Our techniques lead to improvements in all of the above questions, and in several cases partially optimal constructions. This is in contrast to all previous work, which only obtain close to optimal constructions. Specifically, we obtain:

1. A seeded non-malleable extractor with seed length $O(\log n)+\log^{1+o(1)}(1/\epsilon)$ and entropy requirement $O(\log \log n+\log(1/\epsilon))$, where the entropy requirement is asymptotically optimal by a recent result of Gur and Shinkar [GurS17];

2. A two-round privacy amplification protocol with optimal entropy loss for security parameter up to $\Omega(k)$, which solves the privacy amplification problem completely;

3. A two-source extractor for entropy $O(\frac{\log n \log \log n}{\log \log \log n})$, which also gives an explicit Ramsey graph on $N$ vertices with no clique or independent set of size $(\log N)^{O(\frac{\log \log \log N}{\log \log \log \log N})}$; and

4. The first explicit non-malleable code in the $2$-split state model with constant rate, which has been a major goal in the study of non-malleable codes for quite some time. One small caveat is that the error of this code is only (an arbitrarily small) constant, but we can also achieve negligible error with rate $\Omega(\log \log \log n/\log \log n)$, which already improves the rate in [Li17] exponentially.

We believe our new techniques can help to eventually obtain completely optimal constructions in the above questions, and may have applications in other settings.

Backdooring cryptographic algorithms is an indisputable taboo in the cryptographic literature for a good reason: however noble the intentions, backdoors might fall in the wrong hands, in which case security is completely compromised. Nonetheless, more and more legislative pressure is being produced to enforce the use of such backdoors.

In this work we introduce the concept of {\em dispensable cryptographic backdoors} which can be used only once and become useless after that. These exotic primitives are impossible in the classical digital world without stateful and secure trusted hardware support, but, as we show, are feasible assuming quantum computation and access to classical stateless hardware tokens.

Concretely, we construct a dispensable (single-use) version of message authentication codes, and use them to derive a black-box construction of stateful hardware tokens in the above setting with quantum computation and classical stateless hardware tokens. This can be viewed as a generic transformation from stateful to stateless tokens and enables, among other things, one-time programs and memories.

We then use the latter primitives to propose a resolution to the most prominent recent legislative push in favor of backdooring cryptography: the conflict between Apple and FBI last year. We show that it is possible for Apple to create a one-time backdoor which unlocks any single device, and no more than one, i.e., the backdoor becomes useless after it is used. We further describe how to use our ideas to derive a version of CCA-secure public key encryption, which is accompanied with a dispensable (i.e, single-use, as in the above scenario) backdoor.

Offset Public Permutation Mode (OPP) by Granger et al. is a one-pass authenticated encryption scheme supporting associated data (AEAD scheme). Leveraging an error in analysis of the scheme, a chosen plaintext attack that creates a forgery was discovered. This attack makes no assumptions about the underlying tweakable blockcipher while having negligible complexity requirements and high probability of success. An implementation of the attack is also provided.

Silicon Physically Unclonable Functions (PUFs) have been proposed as an emerging hardware security primitive in various applications such as device identification, authentication and cryptographic key generation. Despite their potential, PUF designs based on the Arbiter PUF (APUF) are vulnerable to classical machine learning attacks, which use challenge response pairs. Classical machine learning can be mitigated in the $x$-XOR APUF when enough APUF components have been employed (high $x$). However, reliability based machine learning attacks cannot be prevented by increasing $x$. In this paper, we study the most prominent reliability based machine learning attack, the CMA-ES reliability attack. This work is the first to provide analysis and experimentation to explain under which conditions the CMA-ES reliability attack succeeds and where it fails. Based on these insights, we develop two key contributions. First, we demonstrate how the accuracy of the CMA-ES reliability attack can be improved through enhanced modeling. Second, we propose a new PUF design, the $(x,y)$-Interpose PUF. Through theory and simulation, we show our new PUF model is not vulnerable to the CMA-ES reliability attack, classical machine learning attacks and special attacks that approximate the Interpose PUF as an XOR APUF. In addition, we determine that the security of the IPUF can be reduced to the security of an XOR APUF under classical machine learning attacks, whose complexity depends exponentially on the number of component APUFs in the XOR APUF as shown in the literature. We also show our proposed $(x,y)$-Interpose PUF design is twice as reliable as an $(x+y)$ XOR APUF while using the same hardware overhead as an $(x+y)$ XOR APUF.

We conduct a multi-faceted investigation of the security properties of the three deterministic random bit generator (DRBG) mechanisms recommended in the NIST SP 800-90A standard [4]. This standard received a considerable amount of negative attention, due to the host of controversy and problems with the now retracted DualEC-DRBG, which was included in earlier revisions. Perhaps because of the attention paid to the DualEC, the other algorithms in the standard have received surprisingly patchy analysis to date, despite widespread deployment. This paper provides an analysis of the remaining DRBG algorithms in NIST SP 800-90A. We uncover a mix of positive and less than positive results, emphasizing and addressing the gap between theoretical models, and the NIST DRBGs as specified and used. As an initial positive result, we verify claims in the standard by proving (with a few caveats) the forward security of all three DRBGs. However, digging deeper into flexibility in implementation and usage choices permitted by the standard, we uncover some undesirable properties of these standardized DRBGs. Specifically, we argue that these DRBGs have the property that leaking certain parts of the state may lead to catastrophic failure of the algorithm. Furthermore, we show that flexibility in the specification allows implementers and users of these algorithms to make choices that considerably weaken the algorithms in these scenarios.

Monero is one of the privacy-preserving cryptocurrencies employing CryptoNote protocol. The privacy features in Monero are provided by cryptographic techniques called linkable ring signature and one-time public key. Recent studies show that the majority of Monero inputs are traceable prior to mandatory RingCT transaction. After the RingCT was implemented, the problem was mitigated. We propose a novel attack to reduce the anonymity of Monero transactions or even to fully deanonymise the inputs. The proposed protocol can be launched in RingCT scenario and enable multiple attackers to collaborate without trusting each other. The attack scheme can be planted in the existing Monero services without extra fees and without putting the users’ money at risk.

Postdoc and PhD in cryptographic currencies and anti-surveillance at University of Edinburgh

Worried about surveillance? Imagining a world in which all data is encrypted? Concerned about mistakes in security proofs and bugs in software? Curious about what blockchain technology will look like after the crypto-currency bubble?

At the University of Edinburgh we design distributed cryptographic techniques to protect user\'s online privacy, based on scientific principles using mathematical proofs. A core enabling component is IOHK‘s Cardano blockchain.

Join as a Postdoc or PhD to work on privacy and anonymity, zero-knowledge and multi-party computation. Multiple positions are available. To apply, send your CV with a cover letter and two letters of recommendation. The positions are available until filled.

Contact: Markulf Kohlweiss, mkohlwei (at) ed.ac.uk, https://homepages.inf.ed.ac.uk/mkohlwei/

More Information:

* University of Edinburgh: http://web.inf.ed.ac.uk/security-privacy

* IOHK: https://iohk.io/

Closing date for applications: 31 May 2018

Multi-Party Computation of Oblivious RAM (MPC ORAM) implements secret-shared random access memory in a way that protects access pattern privacy against a threshold of corruptions. MPC ORAM enables secure computation of any RAM program on large data held by different entities, e.g. MPC processing of database queries on a secret-shared database. MPC ORAM can be constructed by any (client-server) ORAM, but there is an efficiency gap between known MPC ORAM's and ORAM's. Current asymptotically best MPC ORAM is implied by an "MPC friendly" variant of Path-ORAM called Circuit-ORAM, due to Wang et al. However, using garbled circuit for Circuit-ORAM's client implies MPC ORAM which matches Path-ORAM in rounds but increases bandwidth by \Omega(kappa) factor, while using GMW or BGW protocols implies MPC ORAM which matches Path-ORAM in bandwidth, but increases round complexity by \Omega(log n loglog n) factor, for kappa the security parameter and n the memory size.

In this paper we bridge the gap between MPC ORAM and client-server ORAM by showing a specialized 3PC ORAM protocol, i.e. MPC ORAM for 3 parties tolerating 1 fault, which uses only symmetric ciphers and asymptotically matches client-server Path-ORAM in round complexity and for large records also in bandwidth.

Our 3PC ORAM also allows for fast pipelined processing: With post- poned clean-up it processes b=O(log n) accesses in O(b+log n) rounds with O(D+poly(log n)) bandwidth per item, where D is record size.

In this work we provide a traitor tracing construction with ciphertexts that grow polynomially in $\log(n)$ where $n$ is the number of users and prove it secure under the Learning with Errors (LWE) assumption. This is the first traitor tracing scheme with such parameters provably secure from a standard assumption. In addition to achieving new traitor tracing results, we believe our techniques push forward the broader area of computing on encrypted data under standard assumptions. Notably, traitor tracing is substantially different problem from other cryptography primitives that have seen recent progress in LWE solutions. We achieve our results by first conceiving a novel approach to building traitor tracing that starts with a new form of Functional Encryption that we call Mixed FE. In a Mixed FE system the encryption algorithm is bimodal and works with either a public key or master secret key. Ciphertexts encrypted using the public key can only encrypt one type of functionality. On the other hand the secret key encryption can be used to encode many different types of programs, but is only secure as long as the attacker sees a bounded number of such ciphertexts. We first show how to combine Mixed FE with Attribute-Based Encryption to achieve traitor tracing. Second we build Mixed FE systems for polynomial sized branching programs (which corresponds to the complexity class LOGSPACE) by relying on the polynomial hardness of the LWE assumption with super-polynomial modulus-to-noise ratio.

Location information has wide applications in customization and personalization of services, as well as secure authentication and access control. We introduce {\em in-Region Authentication (inRA)}, a novel type of authentication, that allows a prover to prove to a set of cooperating verifiers that they are in possession of the correct secret key, and are inside a specified (policy) region of arbitrary shape. These requirements naturally arise when a privileged service is offered to registered users within an area. Locating a prover without assuming GPS (Global Positioning System) signal however, incurs error. We discuss the challenge of designing secure protocols that have quantifiable error in this setting, define and formalize correctness and security properties of the protocols, and propose a systematic approach to designing a family of protocols with provable security where error can be flexibly defined and efficiently minimized. We give a concrete instance of this family that starts with two verifiers, prove its security and evaluate its application to four different policy regions. Our results show that in all cases false acceptance and false rejection of below $6\%$ can be achieved. We compare our results with related works, and propose directions for future research.

Private Set Intersection (PSI) is a popular cryptographic primitive that allows two parties, a client and a server, to compute the intersection of their private sets, so that the client only receives the output of the computation, while the server learns nothing besides the size of the client's set. A common limitation of PSI is that a dishonest client can progressively learn the server's set by enumerating it over different executions. Although these ``oracle attacks'' do not formally violate security according to traditional secure computation definitions, in practice, they often hamper real-life deployment of PSI instantiations, especially if the server's set does not change much over multiple interactions.

In a first step to address this problem, this paper presents and studies the concept of Reactive PSI (RePSI). We model PSI as a reactive functionality, whereby the output depends on previous instances, and use it to limit the effectiveness of oracle attacks. We introduce a general security model for RePSI in the (augmented) semi-honest model and a construction which enables the server to control how many inputs have been used by the client across several executions. In the process, we also present the first construction of a Size-Hiding PSI (SHI-PSI) protocol in the standard model, which may be of independent interest.

This work introduces the concept of flexible signatures. In a flexible signature scheme, the verification algorithm quantifies the validity of a signature based on the number of computations performed such that the signature's validation (or confidence) level in $[0,1]$ improves as the algorithm performs more computations. Importantly, the definition of flexible signatures does not assume the resource restriction to be known in advance until the verification process is hard stopped by a system interrupt. Although prominent traditional signature schemes such as RSA, (EC)DSA, EdDSA seem unfit towards building flexible signatures, we find updated versions of the Lamport-Diffie one-time signature and Merkle authentication tree to be suitable for building flexible signatures. We present a flexible signature construction based on these hash-based primitives and prove its security with a concrete security analysis. We also perform a thorough validity-level analysis demonstrating an attractive computation-vs-validity trade-off offered by our construction: a security level of $80$ bits can be ensured by performing only around $\frac{2}{3}$rd of the total hash computations for our flexible signature construction with a Merkle tree of height $20$.

We see this work as the first step towards realizing flexible-security cryptographic primitives. Beyond flexible signatures, our flexible-security conceptualization offers an interesting opportunity to build similar primitives in the asymmetric as well as symmetric cryptographic domains. Apart from being theoretically interesting, these flexible security primitives can be of particular interest to real-time systems as well as the Internet of things: rigid all-or-nothing guarantees offered by the traditional cryptographic primitives have been particularly unattractive to these unpredictably resource-constrained

This paper presents MergeMAC, a MAC that is particularly suitable for environments with strict time requirements and extremely limited bandwidth. MergeMAC computes the MAC by splitting the message into two parts. We use a pseudorandom function (PRF) to map messages to random bit strings and then merge them with a very efficient keyless function. The advantage of this approach is that the outputs of the PRF can be cached for frequently needed message parts. We demonstrate the merits of MergeMAC for authenticating messages on the CAN bus where bandwidth is extremely limited and caching can be used to recover parts of the message counter instead of transmitting it. We recommend an instantiation of the merging function MERGE and analyze the security of our construction. Requirements for a merging function are formally defined and the resulting EUF-CMA security of MergeMAC is proven.

Authenticated ciphers, like all physical implementations of cryptography, are vulnerable to side-channel attacks, including differential power analysis (DPA). The t-test leakage detection methodology has been used to verify improved resistance of block ciphers to DPA after application of countermeasures. However, extension of the t-test methodology to authenticated ciphers is non-trivial, since authenticated ciphers require additional input and output conditions, complex interfaces, and long test vectors interlaced with protocol necessary to describe authenticated cipher operations. In this research we augment an existing side-channel analysis architecture (FOBOS) with t-test leakage detection for authenticated ciphers. We use this capability to show that implementations in the Spartan-6 FPGA of the CAESAR Round 3 candidates ACORN, ASCON, CLOC (AES and TWINE), SILC (AES, PRESENT, and LED), JAMBU (AES and SIMON), and Ketje Jr., as well as AES-GCM, are vulnerable to 1st order DPA. We then implement versions of the above ciphers, protected against 1st order DPA, using threshold implementations. The t-test leakage detection methodology is used to verify improved resistance to 1st order DPA of the protected cipher implementations. Finally, we benchmark unprotected and protected cipher implementations in the Spartan-6 FPGA, and compare the costs of 1st order DPA protection in terms of area, frequency, throughput, throughput-to-area (TP/A) ratio, power, and energy-per-bit. Our results show that ACORN has the lowest area (in LUTs), the highest TP/A ratio, and is the most energy-efficient of all DPA-resistant implementations. However, Ketje Jr. has the highest throughput.

In this paper, we introduce the notion of delegatable attribute-based anonymous credentials (DAAC). Such systems offer fine-grained anonymous access control and they give the credential holder the ability to issue more restricted credentials to other users. In our model, credentials are parameterized with attributes that (1) express what the credential holder himself has been certified and (2) define which attributes he may issue to others. Furthermore, we present a practical construction of DAAC. For this construction, we deviate from the usual approach of embedding a certificate chain in the credential. Instead, we introduce a novel approach for which we identify a new primitive we call dynamically malleable signatures (DMS) as the main ingredient. This primitive may be of independent interest. We also give a first instantiation of DMS with efficient protocols.

RankSign is a code-based signature scheme proposed to the NIST competition for post-quantum cryptography [AGHRZ17]. It is based on the rank metric and enjoys remarkably small key sizes, about 10KBytes for an intended level of security of 128 bits. It is also one of the fundamental blocks used in the rank metric identity based encryption scheme [GHPT17]. Unfortunately we will show that all the parameters proposed for this scheme in [AGHRZ17] can be broken by an algebraic attack that exploits the fact that the augmented LRPC codes used in this scheme have very low weight codewords.

Intuit is seeking an experienced cryptographer to help us secure the financial information of millions of customers and small businesses. Intuit Security R&D develops services where security and cryptography are used in industry-unique ways to protect our customers' data at the highest security standards.

Responsibilities:

• Participate in driving internal key management and encryption services, providing the business units with the best cryptography while keeping a complex and widespread system secure
• Use the latest research and conduct original research to allow operations over encrypted data, where the data is highly sensitive and solutions need to scale to a very high volume of concurrent transactions
• Validate newly developed cryptographic protocols using both manual proofs and automated formal verification
• Publish regularly as an active participant in the academic cryptographic community, and ensure Intuit is up to date on the latest cryptographic research
• Cooperate with engineering teams to ensure quality implementation of cryptographic protocols
• Work across a diverse and geographically distributed team, maintaining excellent communication and trust

Qualifications

• PhD from a credible institution with a focus on cryptography
• At least 3 years of experience working with industry in the cryptography domain
• At least 2 years of experience designing and developing software
• Proven experience with security issues outside of cryptography is highly desired
• Candidates should possess strong written and oral communication skills
• Demonstrated experience with developing partnerships to influence across organizational boundaries

The preferred location for this position is either Hod Hasharon, Israel or Mountain View, CA, however we are willing to consider other locations.

Closing date for applications: 15 August 2018

Contact: Yaron Sheffer, Director, Security Technologies Product Development, yaron_sheffer at intuit.com.

More information: https://careers.intuit.com/job-category/1/software-engineering/job/00132574/principal-cryptography-researcher