ALBATROSS: Publicly AttestabLe BATched Randomness Based On Secret Sharing

In this paper we present ALBATROSS, a family of multiparty randomness generation protocols with guaranteed output delivery and public verification that allows to trade off corruption tolerance for a much improved amortized computational complexity. Our basic stand alone protocol is based on publicly verifiable secret sharing (PVSS) and is secure under in the random oracle model under the decisional Diffie-Hellman (DDH) hardness assumption. We also address the important issue of constructing Universally Composable randomness beacons, showing two UC versions of Albatross: one based on simple UC NIZKs and another one based on novel efficient ``designated verifier\u27\u27 homomorphic commitments. Interestingly this latter version can be instantiated from a global random oracle under the weaker Computational Diffie-Hellman (CDH) assumption. An execution of ALBATROSS with $n$ parties, out of which up to $t=(1/2-\epsilon)\cdot n$ are corrupt for a constant $\epsilon>0$, generates $\Theta(n^2)$ uniformly random values, requiring in the worst case an amortized cost per party of $\Theta(\log n)$ exponentiations per random value. We significantly improve on the SCRAPE protocol (Cascudo and David, ACNS 17), which required $\Theta(n^2)$ exponentiations per party to generate one uniformly random value. This is mainly achieved via two techniques: first, the use of packed Shamir secret sharing for the PVSS; second, the use of linear $t$-resilient functions (computed via a Fast Fourier Transform-based algorithm) to improve the randomness extraction

Increased Resilience in Threshold Cryptography: Sharing a Secret with Devices That Cannot Store Shares

Threshold cryptography has been used to secure data and control access by sharing a private cryptographic key over different devices. This means that a minimum number of these devices, the threshold $t+1$, need to be present to use the key. The benefits are increased security, because an adversary can compromise up to $t$ devices, and resilience, since any subset of $t+1$ devices is sufficient. Many personal devices are not suitable for threshold schemes, because they do not offer secure storage, which is needed to store shares of the private key. This article presents several protocols in which shares are stored in protected form (possibly externally). This makes them suitable for low-cost devices with a factory-embedded key, e.g., car keys and access cards. All protocols are verifiable through public broadcast, thus without private channels. In addition, distributed key generation does not require all devices to be present

Boy Scout camp (2)

Abstract. Protocol for fair exchange of digital signatures is essential in many applications including contract signing, electronic commerce, or even peer-to-peer file sharing. In such a protocol, two parties, Alice and Bob, would like to exchange digital signatures on some messages in a fair way. It is known that a trusted arbitrator is necessary in the realization of such a protocol. We identify that in some scenarios, it is required that prior to the completion of the protocol, no observer should be able to tell whether Alice and Bob are conducting such an exchange. Consider the following scenario in which Apple engages Intel in an exchange protocol to sign a contract that terminates their OEM agreement. The information would be of value to a third party (such as the stock broker, or other OEM companies). If the protocol transcript can serve as an evidence that such a communication is in progress, any observer of this communication, including the employees of both companies, would be tempted to capture the transcript and sell it to outsiders. We introduce a new notion called perfect ambiguous optimistic fair exchange (PAOFE), which is particularly suitable to the above scenario. PAOFE fulfils all traditional requirements of cryptographic fair exchange of digital signatures and, in addition, guarantees that the communication transcript cannot be used as a proof to convince others that the protocol is in progress. Specifically, we formalize the notion of PAOFE and present a rigorous security model in the multi-user setting under the chosen-key attack. We also present a generic construction of PAOFE from existing cryptographic primitives and prove that our proposal is secure with respect to our definition in the standard model.

SCRAPE:Scalable randomness attested by public entities

Uniform randomness beacons whose output can be publicly attested to be unbiased are required in several cryptographic protocols. A common approach to building such beacons is having a number parties run a coin tossing protocol with guaranteed output delivery (so that adversaries cannot simply keep honest parties from obtaining randomness, consequently halting protocols that rely on it). However, current constructions face serious scalability issues due to high computational and communication overheads. We present a coin tossing protocol for an honest majority that allows for any entity to verify that an output was honestly generated by observing publicly available information (even after the execution is complete), while achieving both guaranteed output delivery and scalability. The main building block of our construction is the first Publicly Verifiable Secret Sharing scheme for threshold access structures that requires only O(n) exponentiations. Previous schemes required O(nt) exponentiations (where t is the threshold) from each of the parties involved, making them unfit for scalable distributed randomness generation, which requires t=n/2 and thus O(n^2) exponentiations

Exogenous progesterone application protects chickpea seedlings against chilling-induced oxidative stress

This experiment was conducted to monitor the influence of foliar progesterone application on the chilling tolerance of chickpea seedlings. Twelve-day-old chickpea seedlings were treated with 10(-7) mol L-1 progesterone. After 12 h, the seedlings were exposed to day/night temperatures of 9/5 A degrees C for 72 h in a growth chamber. Chilling stress resulted in remarkable increase in the activities of antioxidant enzymes including superoxide dismutase (SOD), guaicol peroxidase (POX), catalase, ascorbate peroxidase (APX) and glutathione reductase, as well as the level of antioxidant compounds like ascorbic acid, glutathione and proline. In a similar manner, chilling stress affected significantly oxidative stress indicators measured as superoxide production, electrolyte leakage, hydrogen peroxide (H2O2) and malondialdehyde contents. The values of these parameters were lesser in progesterone-applied seedlings that were associated with higher activities of antioxidant enzymes and greater levels of antioxidant compounds in these seedlings. A highly significant correlation was recorded between SOD, POX and APX activities and their isozymes. This correlation confirmed enhanced activities of these enzymes. In addition, progesterone application ameliorated chilling-induced decrease in relative leaf water content (RLWC) and chlorophyll content. Freezing tolerance, showed by thermal analysis method, proved that progesterone application improved chilling tolerance of chickpea seedlings by lowering freezing point from -4 to -5.5 A degrees C. It is possible that chilling tolerance induced by progesterone is related to elevation of RLWC, chlorophyll content and antioxidative activity, and thereby decrease in oxidative stress indicators