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04:17 [Pub][ePrint] Armadillo: a compilation chain for privacy preserving applications, by Sergiu Carpov and Paul Dubrulle and Renaud Sirdey

  In this work we present Armadillo a compilation chain used for compiling applications written in a high-level language (C++) to work on encrypted data. The back-end of the compilation chain is based on homomorphic encryption. The tool-chain further automatically handle a huge amount of parallelism so as to mitigate the performance overhead of using homomorphic encryption.

04:17 [Pub][ePrint] Controlled Homomorphic Encryption: Definition and Construction, by Yvo Desmedt and Vincenzo Iovino and Giuseppe Persiano and Ivan Visconti

  Fully Homomorphic Encryption schemes (FHEs) and Functional Encryption schemes (FunctEs) have a tremendous impact in Cryptography both for the natural questions that they address and for the wide range of applications in which they have been (sometimes critically) used. In this work we put forth the notion of a Controllable Homomorphic Encryption scheme (CHES), a new primitive that includes features of both FHEs and FunctEs. In a CHES it is possible (similarly to a FHE) to homomorphically evaluate a ciphertext Ct = Enc(m) and a circuit C therefore obtaining Enc(C(m)) but only if (similarly to a FunctE) a token for C has been received from the owner of the secret key. We discuss difficulties in constructing a CHES and then show a construction based on any FunctE.

04:17 [Pub][ePrint] Combining Secret Sharing and Garbled Circuits for Efficient Private IEEE 754 Floating-Point Computations, by Pille Pullonen and Sander Siim

  Two of the major branches in secure multi-party computation research are secret sharing and garbled circuits. This work succeeds in combining these to enable seamlessly switching to the technique more efficient for the required functionality. As an example, we add garbled circuits based IEEE 754 floating-point numbers to a secret sharing environment achieving very high efficiency and the first, to our knowledge, fully IEEE 754 compliant secure floating-point implementation.

04:17 [Pub][ePrint] Constant Round Concurrent Zero-knowledge from Indistinguishability Obfuscation, by Kai-Min Chung and Huijia Lin and Rafael Pass

  We present a constant-round concurrent zero-knowledge protocol for NP. Our protocol relies on the existence of families of collision-resistant hash functions, one-way permutations, and indistinguishability obfuscators for P/poly (with slightly super-polynomial security).

04:17 [Pub][ePrint] Incentivized Outsourced Computation Resistant to Malicious Contractors, by Alptekin Kupcu

  With the rise of Internet computing, outsourcing difficult computational tasks became an important need. Yet, once the computation is outsourced, the job owner loses control, and hence it is crucial to provide guarantees against malicious actions of the contractors involved. Cryptographers have an almost perfect solution, called fully homomorphic encryption, to this problem. This solution hides both the job itself and any inputs to it from the contractors, while still enabling them to perform the necessary computation over the encrypted data. This is a very strong security guarantee, but the current constructions are highly impractical.

In this paper, we propose a different approach to outsourcing computational tasks. We are not concerned with hiding the job or the data, but our main task is to ensure that the job is computed correctly. We also observe that not all contractors are malicious; rather, majority are rational. Thus, our approach brings together elements from cryptography, as well as game theory and mechanism design. We achieve the following results: (1) We incentivize all the rational contractors to perform the outsourced job correctly, (2) we guarantee high fraction (e.g., 99.9%) of correct results even in the existence of a relatively large fraction (e.g., 33%) of malicious irrational contractors in the system, (3) and we show that our system achieves these while being almost as efficient as running the job locally (e.g., with only 3% overhead). Such a high correctness guarantee was not known to be achieved with such efficiency.

04:17 [Pub][ePrint] How Different Electrical Circuits of ECC Designs Influence the Shape of Power Traces measured on FPGA, by Thomas Basmer and Christian Wittke and Zoya Dyka and Peter Langendoerfer

  Side channel and fault attacks take advantage from the fact that the behavior of crypto implementations can be observed and provide hints that simplify revealing keys. These attacks use identical devices either for preparation of attacks or for measurements. By the preparation of attacks the structure and the electrical circuit of devices, that are identical to the target, is analyzed. By side channel attacks usually the same device is used many times for measurements, i.e. measurements on the identical device are made serially in time. Another way is to exploit the difference of side channel leakages; here two identical devices are used parallel, i.e. at the same time. In this paper we investigate the influence of the electrical circuit of a cryptographic implementation on the shape of the resulting power trace, because individualizing of circuits of cryptographic devices can be a new means to prevent attacks that use identical devices. We implemented three different designs that provide exactly the same cryptographic function, i.e. an ECC kP multiplication. For our evaluation we use two different FPGAs. The visualization of the routed design and measurement results show clear differences in the resources consumed as well as in the power traces.

04:17 [Pub][ePrint] Two novel applications of bilinear groups to ABE encryption, by Riccardo Longo and Chiara Marcolla and Massimiliano Sala

  Bilinear groups are often used to create Attribute-Based Encryption (ABE) algorithms.

In particular, they have been used to create an ABE system with multi authorities, but limited to the ciphertext-policy instance.

Here, for the first time, we propose two multi-authority key-policy ABE systems.

In our first proposal, the authorities may be set up in any moment and without any coordination.

A party can simply act as an ABE authority by creating its own public parameters and issuing private keys to the users.

A user can thus encrypt data choosing both a set of attributes and a set of trusted authorities, maintaining full control unless all his chosen authorities collude against him.

In our second system, the authorities are allowed to collaborate to achieve shorter keys and parameters, enhancing the efficiency of encryption and decryption.

We prove our systems secure under algebraic assumptions on the bilinear groups: the bilinear Diffie-Hellmann assumption and an original variation of the former.

04:17 [Pub][ePrint] Partial Garbling Schemes and Their Applications, by Yuval Ishai and Hoeteck Wee

  Garbling schemes (aka randomized encodings of functions) represent a function F by a \"simpler\" randomized function F^ such that F^(x) reveals F(x) and no additional information about x. Garbling schemes have found applications in many areas of cryptography. Motivated by the goal of improving the efficiency of garbling schemes, we make the following contributions:

- We suggest a general new notion of partial garbling which unifies several previous notions from the literature, including standard garbling schemes, secret sharing schemes, and \"conditional disclosure of secrets\". This notion considers garbling schemes in which part of the input is public, in the sense that it can be leaked by F^.

- We present constructions of partial garbling schemes for (boolean and arithmetic) formulas and branching programs which take advantage of the public input to gain better efficiency.

- We demonstrate the usefulness of the new notion by presenting applications to efficient attribute-based encryption, delegation, and secure computation. In each of these applications, we obtain either new schemes for larger classes of functions or efficiency improvements from quadratic to linear. In particular, we obtain the first ABE scheme in bilinear groups for arithmetic formulas, as well as more efficient delegation schemes for boolean and arithmetic branching programs.

04:17 [Pub][ePrint] Some experiments investigating a possible L(1/4) algorithm for the discrete logarithm problem in algebraic curves, by Maike Massierer

  The function field sieve, a subexponential algorithm of complexity L(1/3) that computes discrete logarithms in finite fields, has recently been improved to an algorithm of complexity L(1/4) and subsequently to a quasi-polynomial time algorithm. We investigate whether the new ideas also apply to index calculus algorithms for computing discrete logarithms in Jacobians of algebraic curves. While we do not give a final answer to the question, we discuss a number of ideas, experiments, and possible conclusions.

04:17 [Pub][ePrint] Ring ORAM: Closing the Gap Between Small and Large Client Storage Oblivious RAM, by Ling Ren and Christopher W. Fletcher and Albert Kwon and Emil Stefanov and Elaine Shi and Marten van Dijk and Sriniv

  We present Ring ORAM, a simple and low-latency ORAM construction that can be parameterized for either small or large client storage.

Simply by tuning parameters, Ring ORAM matches or exceeds the performance of the best-known small and large client storage schemes and can achieve a constant factor online bandwidth overhead over insecure systems.

We evaluate Ring ORAM in theory and in practice.

On the theory side, we prove that Ring ORAM matches the asymptotic bandwidth and client storage of Path ORAM, the prior-art scheme for small client storage.

Tuning parameters for small client storage, Ring ORAM reduces overall bandwidth relative to Path ORAM by a factor of $2.7\\times$ and reduces online bandwidth to constant (a $57\\times$ improvement over Path ORAM given realistic parameters).

Tuning parameters for large client storage, Ring ORAM outperforms Path ORAM (which is given equal storage) by $4.5\\times$ and SSS ORAM, the prior-art scheme for large client storage, by 16-33\\%.

Using secure processors as a case study for small client storage, Ring ORAM on average reduces ORAM response time by nearly $5\\times$ and improves workload completion time by $2.75\\times$, relative to Path ORAM.

In the large storage setting, running an enterprise file system trace with bursty requests, Ring ORAM adds negligible overhead to response time given a $>100$~Mbps network bandwidth.

By comparison, Burst ORAM incurs large overheads in response time unless network bandwidth $>350$~Mbps.

These results suggest that Ring ORAM is a compelling construction in both large client storage (e.g., file server) and small client storage (e.g., remote secure processor) settings.

04:17 [Pub][ePrint] Hierarchical deterministic Bitcoin wallets that tolerate key leakage, by Gus Gutoski and Douglas Stebila

  A Bitcoin wallet is a set of private keys known to a user and which allow that user to spend any Bitcoin associated with those keys. In a hierarchical deterministic (HD) wallet, child private keys are generated pseudorandomly from a master private key, and the corresponding child public keys can be generated by anyone with knowledge of the master public key. These wallets have several interesting applications including Internet retail, trustless audit, and a treasurer allocating funds among departments. A specification of HD wallets has even been accepted as Bitcoin standard BIP32.

Unfortunately, in all existing HD wallets---including BIP32 wallets---an attacker can easily recover the master private key given the master public key and any child private key. This vulnerability precludes use cases such as a combined treasurer-auditor, and some in the Bitcoin community have suspected that this vulnerability cannot be avoided.

We propose a new HD wallet that is not subject to this vulnerability. Our HD wallet can tolerate the leakage of up to m private keys with a master public key size of O(m). We prove that breaking our HD wallet is at least as hard as the so-called ``one more\'\' discrete logarithm problem.