Shielded CSV: Private and Efficient Client-Side Validation

Cryptocurrencies allow mutually distrusting users to transact monetary value over the internet without relying on a trusted third party. Bitcoin, the first cryptocurrency, achieved this through a novel protocol used to establish consensus about an ordered transaction history. This requires every transaction to be broadcasted and verified by the network, incurring communication and computational costs. Furthermore, transactions are visible to all nodes of the network, eroding privacy, and are recorded permanently, contributing to increasing storage requirements over time. To limit resource usage of the network, Bitcoin currently supports an average of 11 transactions per second. Most cryptocurrencies today still operate in a substantially similar manner. Private cryptocurrencies like Zcash and Monero address the privacy issue by replacing transactions with proofs of transaction validity. However, this enhanced privacy comes at the cost of increased communication, storage, and computational requirements. Client-Side Validation (CSV) is a paradigm that addresses these issues by removing transaction validation from the blockchain consensus rules. This approach allows sending the coin along with a validity proof directly to its recipient, reducing communication, computation and storage cost. CSV protocols deployed on Bitcoin today do not fully leverage the paradigm\u27s potential, as they still necessitate the overhead of publishing ordinary Bitcoin transactions. Moreover, the size of their coin proofs is proportional to the coin\u27s transaction history, and provide limited privacy. A recent improvement is the Intmax2 CSV protocol, which writes significantly less data to the blockchain compared to a blockchain transaction and has succinct coin proofs. In this work, we introduce Shielded CSV, which improves upon state-of-the-art CSV protocols by providing the first construction that offers truly private transactions. It addresses the issues of traditional private cryptocurrency designs by requiring only 64 bytes of data per transaction, called a nullifier, to be written to the blockchain. Moreover, for each nullifier in the blockchain, Shielded CSV users only need to perform a single Schnorr signature verification, while non-users can simply ignore this data. The size and verification cost of coin proofs for Shielded CSV receivers is independent of the transaction history. Thus, one application of Shielded CSV is adding privacy to Bitcoin at a rate of 100 transactions per second, provided there is an adequate bridging mechanism to the blockchain. We specify Shielded CSV using the Proof Carrying Data (PCD) abstraction. We then discuss two implementation strategies that we believe to be practical, based on Folding Schemes and Recursive STARKs, respectively. Finally, we propose future extensions, demonstrating the power of the PCD abstraction and the extensibility of Shielded CSV. This highlights the significant potential for further improvements to the Shielded CSV framework and protocols built upon it

Towards the first direct measurement of the dynamic viscosity of gaseous tritium at cryogenic temperatures

Accurate values for the viscosity of the radioactive hydrogen isotope tritium (T) at cryogenic temperatures are unavailable. Values for tritium found in literature are based on extrapolation by mass ratios as well as an empirical factor derived from hydrogen (H) and deuterium (D ) viscosity measurements, or classical kinetic theory which does not handle quantum effects. Accurate data of the tritium viscosity will help to improve the modelling of the viscosity of diatomic molecules and can be used as a test of their interaction potentials. With this contribution we report a major step towards a fully tritium and cryogenic temperature compatible setup for the accurate measurement of the viscosity of gases, using a spinning rotor gauge (SRG) at the Tritium Laboratory Karlsruhe. After calibration with helium, measurements with hydrogen and deuterium conducted at room temperature agree with literature values within 2%. The performance at liquid nitrogen (LN ) temperature has been successfully demonstrated with a second setup in a liquid nitrogen bath. Again after calibration with helium at LN temperature, the viscosities of H and D were determined and are in agreement with literature to about 2%

Viscosity measurements of gaseous H2 between 200 K to 300 K with a spinning rotor gauge

Experimental values for the viscosity of the radioactive hydrogen isotopologue tritium are still unknown in literature. Existing values from ab initio calculations disregard quantum mechanic effects and are therefore only good approximations for room temperature and above. To fill in these missing experimental values, a measurement setup has been designed, to measure the viscosity of gaseous hydrogen and its isotopologues (H$_2$, HD, HT, D$_2$, DT, T$_2$) at cryogenic temperatures. In this paper, the first results with this Cryogenic Viscosity Measurement Apparatus (Cryo-ViMA) of the viscosity of gaseous hydrogen between 200 K to 300 K are presented.Comment: 9 pages, 2 figures, 22nd International Vacuum Congress, submitted to e-Journal of Surface Science and Nanotechnolog

Effect of Ba(II), Eu(III), and U(VI) on rat NRK-52E and human HEK-293 kidney cells in vitro

Heavy metals pose a potential health risk to humans when they enter the organism. Renal excretion is one of the elimination pathways and, therefore, investigations with kidney cells are of particular interest. In the present study, the effects of Ba(II), Eu(III), and U(VI) on rat and human renal cells were investigated in vitro. A combination of microscopic, biochemical, analytical, and spectroscopic methods was used to assess cell viability, cell death mechanisms, and intracellular metal uptake of exposed cells as well as metal speciation in cell culture medium and inside cells. For Eu(III) and U(VI), cytotoxicity and intracellular uptake are positively correlated and depend on concentration and exposure time. An enhanced apoptosis occurs upon Eu(III) exposure whereas U(VI) exposure leads to enhanced apoptosis and (secondary) necrosis. In contrast to that, Ba(II) exhibits no cytotoxic effect at all and its intracellular uptake is time-independently very low. In general, both cell lines give similar results with rat cells being more sensitive than human cells. The dominant binding motifs of Eu(III) in cell culture medium as well as cell suspensions are (organo-) phosphate groups. Additionally, a protein complex is formed in medium at low Eu(III) concentration. In contrast, U(VI) forms a carbonate complex in cell culture medium as well as each one phosphate and carbonate complex in cell suspensions. Using chemical microscopy, Eu(III) was localized in granular, vesicular compartments near the nucleus and the intracellular Eu(III) species equals the one in cell suspensions. Overall, this study contributes to a better understanding of the interactions of Ba(II), Eu(III), and U(VI) on a cellular and molecular level. Since Ba(II) and Eu(III) serve as inactive analogs of the radioactive Ra(II) and Am(III)/Cm(III), the results of this study are also of importance for the health risk assessment of these radionuclides

Blueprint from nature: Multi-omics comparison of CHO and plasma cells unveils novel cell engineering targets to improve productivity

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Is there a fast track (“Darmstrasse”) for fluids in the small intestine? Evidence from magnetic resonance imaging

Background The transit and distribution pattern of fluids in the small intestine is a key parameter for the dissolution and absorption of drugs. Although some information is known about the small intestinal water content after administration of fluid volumes and meals, the intestinal transit of orally ingested fluids and solutions has been barely investigated. The aim of this three-arm, cross-over, 9-subject human study was to investigate the transit of orally ingested water in the small intestine under fasting and postprandial conditions using MRI. To identify the ingested water, manganese gluconate, which can be identified with T1-weighted MRI sequences, was added as a marker. Using Horos (DICOM software), quantification of the distribution of Mn2+ ions in the gastrointestinal tract in fasted versus fed state (standard meal by FDA guidance and a light meal) was possible. The distribution and approximate wetted intestinal length was very similar in the fasting and postprandial states, suggesting rapid transport of water ingested after a meal through the chyme-filled small intestine in continuation of the “Magenstrasse” (stomach road). In some subjects, manganese gluconate reached deeper parts of the small intestine even more quickly in the postprandial state than in the fasting arm of the study. A deeper understanding of the behaviour of solutes in the gastrointestinal tract is fundamental to a mechanistic explanation for the kinetic interaction between food and drug intake (food effects)

BitVM: Quasi-Turing Complete Computation on Bitcoin

A long-standing question in the blockchain community is which class of computations are efficiently expressible in cryptocurrencies with limited scripting languages, such as Bitcoin Script. Such languages expose a reduced trusted computing base, thereby being less prone to hacks and vulnerabilities, but have long been believed to support only limited classes of payments. In this work, we confute this long-standing belief by showing for the first time that arbitrary computations can be encoded in today\u27s Bitcoin Script, without introducing any language modification or additional security assumptions, such as trusted hardware, trusted parties, or committees with secure majority. In particular, we present $\mathsf{BitVM}$, a two-party protocol realizing a generic virtual machine by a combination of cryptographic and incentive mechanisms. We conduct a formal analysis of $\mathsf{BitVM}$, characterizing its functionality, system assumptions, and security properties. We further demonstrate the practicality of our approach: in the optimistic case (i.e., in the absence of disputes between parties), our protocol requires just three on-chain transactions, whereas in the pessimistic case, the number of transactions grows logarithmically with the size of the virtual machine. This work not only solves a long-standing theoretical problem, but it also promises a strong practical impact, enabling the development of complex applications in Bitcoin

Bridging Bitcoin to Second Layers via BitVM2

A holy grail in blockchain infrastructure is a trustless bridge between Bitcoin and its second layers or other chains. We make progress toward this vision by introducing the first light-client based Bitcoin bridge. At the heart of its design lies BitVM2-core, a novel paradigm that enables arbitrary program execution on Bitcoin, combining Turing-complete expressiveness with the security of Bitcoin consensus. BitVM2-bridge advances prior approaches by reducing the trust assumption from an honest majority (t-of-n) to existential honesty (1-of-n) during setup. Liveness is guaranteed with only one rational operator, and any user can act as a challenger, enabling permissionless verification. A production-level implementation of BitVM2 has been developed and a full challenge verification has been executed on the Bitcoin mainnet

Push-Button Verification for BitVM Implementations

Bitcoin, while being the most prominent blockchain with the largest market capitalization, suffers from scalability and throughput limitations that impede the development of ecosystem projects like Bitcoin Decentralized Finance (BTCFi). Recent advancements in BitVM propose a promising Layer 2 (L2) solution to enhance Bitcoin\u27s scalability by enabling complex computations off-chain with on-chain verification. However, Bitcoin\u27s constrained programming environment—characterized by its non-Turing-complete Script language lacking loops and recursion, and strict block size limits—makes developing complex applications labor-intensive, error-prone, and necessitates manual partitioning of scripts. Under this complex programming model, subtle mistakes could lead to irreversible damage in a trustless environment like Bitcoin. Ensuring the correctness and security of such programs becomes paramount. To address these challenges, we introduce the first formal verifier for BitVM implementations. Our approach involves designing a register-based, higher-level domain-specific language (DSL) that abstracts away complex stack operations, allowing developers to reason about program correctness more effectively while preserving the semantics of the low-level program. We present a formal computational model capturing the semantics of BitVM execution and Bitcoin script, providing a foundation for rigorous verification. To efficiently handle large programs and complex constraints arising from unrolled computations that simulate loops, we summarize repetitive loop-style computations using loop invariant predicates in our DSL. We leverage a counterexample-guided inductive synthesis (CEGIS) procedure to lift low-level Bitcoin script into our DSL, facilitating efficient verification without sacrificing accuracy. Evaluated on 78 benchmarks from BitVM implementations, our tool successfully verifies 83% of cases within 12.55 seconds on average and identified one previously unknown vulnerability, demonstrating its effectiveness in enhancing the security and reliability of BitVM