Efficient noninteractive certification of RSA moduli and beyond

In many applications, it is important to verify that an RSA public key (N; e) speci es a permutation over the entire space ZN, in order to prevent attacks due to adversarially-generated public keys. We design and implement a simple and e cient noninteractive zero-knowledge protocol (in the random oracle model) for this task. Applications concerned about adversarial key generation can just append our proof to the RSA public key without any other modi cations to existing code or cryptographic libraries. Users need only perform a one-time veri cation of the proof to ensure that raising to the power e is a permutation of the integers modulo N. For typical parameter settings, the proof consists of nine integers modulo N; generating the proof and verifying it both require about nine modular exponentiations. We extend our results beyond RSA keys and also provide e cient noninteractive zero- knowledge proofs for other properties of N, which can be used to certify that N is suitable for the Paillier cryptosystem, is a product of two primes, or is a Blum integer. As compared to the recent work of Auerbach and Poettering (PKC 2018), who provide two-message protocols for similar languages, our protocols are more e cient and do not require interaction, which enables a broader class of applications.https://eprint.iacr.org/2018/057First author draf

Chosen-ciphertext security from subset sum

We construct a public-key encryption (PKE) scheme whose security is polynomial-time equivalent to the hardness of the Subset Sum problem. Our scheme achieves the standard notion of indistinguishability against chosen-ciphertext attacks (IND-CCA) and can be used to encrypt messages of arbitrary polynomial length, improving upon a previous construction by Lyubashevsky, Palacio, and Segev (TCC 2010) which achieved only the weaker notion of semantic security (IND-CPA) and whose concrete security decreases with the length of the message being encrypted. At the core of our construction is a trapdoor technique which originates in the work of Micciancio and Peikert (Eurocrypt 2012

Managing Individual Workplace Grievances and Disciplinary Procedures

This paper examines ways of effectively managing individual workplace grievances and disciplinary procedures. There are three principle areas that will be the focus of this page: • dealing with conflict between co-workers; • managing workplace complaints and investigation procedures; and • implementing appropriate disciplinary procedures. These issues on the whole tend to be aired in the course of unfair dismissal proceedings, when the substantive and procedural fairness of a dismissal is considered. However, good HR practices should ensure that the issues are well managed from the outset through established procedures, long before the issue of unfair dismissal arises

Ciphertext Expansion in Limited-Leakage Order-Preserving Encryption: A Tight Computational Lower Bound

Order-preserving encryption emerged as a key ingredient underlying the security of practical database management systems. Boldyreva et al. (EUROCRYPT \u2709) initiated the study of its security by introducing two natural notions of security. They proved that their first notion, a ``best-possible\u27\u27 relaxation of semantic security allowing ciphertexts to reveal the ordering of their corresponding plaintexts, is not realizable. Later on Boldyreva et al. (CRYPTO \u2711) proved that any scheme satisfying their second notion, indistinguishability from a random order-preserving function, leaks about half of the bits of a random plaintext. This unsettling state of affairs was recently changed by Chenette et al. (FSE \u2716), who relaxed the above ``best-possible\u27\u27 notion and constructed a scheme satisfying it based on any pseudorandom function. In addition to revealing the ordering of any two encrypted plaintexts, ciphertexts in their scheme reveal only the position of the most significant bit on which the plaintexts differ. A significant drawback of their scheme, however, is its substantial ciphertext expansion: Encrypting plaintexts of length $m$ bits results in ciphertexts of length $m \cdot \ell$ bits, where $\ell$ determines the level of security (e.g., $\ell = 80$ in practice). In this work we prove a lower bound on the ciphertext expansion of any order-preserving encryption scheme satisfying the ``limited-leakage\u27\u27 notion of Chenette et al. with respect to non-uniform polynomial-time adversaries, matching the ciphertext expansion of their scheme up to lower-order terms. This improves a recent result of Cash and Zhang (ePrint \u2717), who proved such a lower bound for schemes satisfying this notion with respect to computationally-unbounded adversaries (capturing, for example, schemes whose security can be proved in the random-oracle model without relying on cryptographic assumptions). Our lower bound applies, in particular, to schemes whose security is proved in the standard model

Nonce-Based Cryptography: Retaining Security when Randomness Fails

We take nonce-based cryptography beyond symmetric encryption, developing it as a broad and practical way to mitigate damage caused by failures in randomness, whether inadvertent (bugs) or malicious (subversion). We focus on definitions and constructions for nonce-based public-key encryption and briefly treat nonce-based signatures. We introduce and construct hedged extractors as a general tool in this domain. Our nonce-based PKE scheme guarantees that if the adversary wants to violate IND-CCA security then it must do both of the following: (1) fully compromise the RNG (2) penetrate the sender system to exfiltrate a seed used by the sende

The Fiat-Shamir Zoo: Relating the Security of Different Signature Variants

The Fiat-Shamir paradigm encompasses many different ways of turning a given identification scheme into a signature scheme. Security proofs pertain sometimes to one variant, sometimes to another. We systematically study three variants that we call the challenge (signature is challenge and response), commit (signature is commitment and response) and transcript (signature is challenge, commitment and response) variants. Our framework captures the variants via transforms that determine the signature scheme as a function of not only the identification scheme and hash function (to cover both standard and random oracle model hashing), but also what we call a signing algorithm, to cover both classical and with-abort signing. We relate the security of the signature schemes produced by these transforms, giving minimal conditions under which uf-security of one transfers to the other. To apply this comprehensively, we formalize linear identification schemes, show that many schemes in the literature are linear, and show that any linear scheme meets our conditions for the signature schemes given by the three transforms to have equivalent uf-security. Our results give a comprehensive picture of the Fiat-Shamir zoo and allow proofs of security in the literature to be transferred automatically from one variant to another

Reversible Decrease of Portal Venous Flow in Cirrhotic Patients: A Positive Side Effect of Sorafenib

Portal hypertension, the most important complication with cirrhosis of the liver, is a serious disease. Sorafenib, a tyrosine kinase inhibitor is validated in advanced hepatocellular carcinoma. Because angiogenesis is a pathological hallmark of portal hypertension, the goal of our study was to determine the effect of sorafenib on portal venous flow and portosystemic collateral circulation in patients receiving sorafenib therapy for advanced hepatocellular carcinoma. Porto-collateral circulations were evaluated using a magnetic resonance technique prior sorafenib therapy, and at day 30. All patients under sorafenib therapy had a decrease in portal venous flow of at least 36%. In contrast, no specific change was observed in the azygos vein or the abdominal aorta. No portal venous flow modification was observed in the control group. Sorafenib is the first anti-angiogenic therapy to demonstrate a beneficial and reversible decrease of portal venous flow among cirrhotic patients

Aurora: Transparent Succinct Arguments for R1CS

We design, implement, and evaluate a zkSNARK for Rank-1 Constraint Satisfaction (R1CS), a widely-deployed NP-complete language that is undergoing standardization. Our construction uses a transparent setup, is plausibly post-quantum secure, and uses lightweight cryptography. A proof attesting to the satisfiability of n constraints has size $O(\log^2 n)$; it can be produced with $O(n \log n)$ field operations and verified with $O(n)$. At 128 bits of security, proofs are less than 130kB even for several million constraints, more than 20x shorter than prior zkSNARK with similar features. A key ingredient of our construction is a new Interactive Oracle Proof (IOP) for solving a *univariate* analogue of the classical sumcheck problem [LFKN92], originally studied for *multivariate* polynomials. Our protocol verifies the sum of entries of a Reed--Solomon codeword over any subgroup of a field. We also provide libiop, an open-source library for writing IOP-based arguments, in which a toolchain of transformations enables programmers to write new arguments by writing simple IOP sub-components. We have used this library to specify our construction and prior ones

On the Security Loss of Unique Signatures

We consider the question of whether the security of unique digital signature schemes can be based on game-based cryptographic assumptions using linear-preserving black-box security reductions—that is, black-box reductions for which the security loss (i.e., the ratio between work of the adversary and the work of the reduction) is some a priori bounded polynomial. A seminal result by Coron (Eurocrypt\u2702) shows limitations of such reductions; however, his impossibility result and its subsequent extensions all suffer from two notable restrictions: (1) they only rule out so-called simple reductions, where the reduction is restricted to only sequentially invoke straight-line instances of the adversary; and (2) they only rule out reductions to non-interactive (two-round) assumptions. In this work, we present the first full impossibility result: our main result shows that the existence of any linear-preserving black-box reduction for basing the security of unique signatures on some bounded-round assumption implies that the assumption can be broken in polynomial time

Post-Quantum EPID Signatures from Symmetric Primitives

EPID signatures are used extensively in real-world systems for hardware enclave attestation. As such, there is a strong interest in making these schemes post-quantum secure. In this paper we initiate the study of EPID signature schemes built only from symmetric primitives, such as hash functions and PRFs. We present two constructions in the random oracle model. The first is a scheme satisfying the EPID signature syntax and security definitions needed for private hardware attestation used in Intel’s SGX. The second achieves significantly shorter signatures for many applications, including the use case of remote hardware attestation. While our EPID signatures for attestation are longer than standard post-quantum signatures, they are short enough for applications where the data being signed is large, such as analytics on large private data sets, or streaming media to a trusted display. We evaluate several instantiations of our schemes so that the costs and benefits of these constructions are clear. Along the way we also give improvements to the zero-knowledge Merkle inclusion proofs of Derler et al. (2017)