DROPS

Document

DOI: 10.4230/LIPIcs.ITCS.2026.6

Model-Generic Incrementally Verifiable Computation from Updatable BARGs

Authors: Eden Aldema Tshuva and Rotem Oshman

Published in: LIPIcs, Volume 362, 17th Innovations in Theoretical Computer Science Conference (ITCS 2026)

Abstract

Incrementally verifiable computation (IVC) is a computationally sound proof system that allows a prover to certify the correctness of a long or ongoing computation in an incremental manner, by repeatedly updating a proof certifying the computation so far. Updating the proof does not require access to the entire trace of the computation, which makes the IVC-prover memory efficient. Recently, such schemes were constructed for deterministic Turing machines from standard cryptographic assumptions (Paneth and Pass, FOCS 2022, and Devadas et al., FOCS 2022). In this work we generalize and extend IVC to support incremental certification and verifiability of a large set of computation models, focusing on distributed and online computation. This allows distributed algorithms to efficiently certify their own execution using low memory and communication overhead. We construct IVC for a variety of computation models by proving one generic lifting theorem from a classical (non-incremental) delegation scheme (also known as SNARG) into full-fledged IVC, while preserving the delegation scheme’s succinctness properties (up to an additive factor which is polynomial in the security parameter and independent of the size of the computation). Using this lifting theorem, we obtain IVC for the following computation models: - RAM and exclusive-read exclusive-write (EREW) PRAM algorithms, using existing delegation schemes for these models. - Streaming algorithms, using the natural memory-efficiency properties of the model. - Massively parallel computation (MPC). Notably, in this model, memory efficiency is a critical bottleneck: the machines participating in an MPC algorithm usually cannot store the entire trace of their computation. Thus, certifying MPC algorithms naturally benefits from IVC. Moreover, since prior to our work, no delegation scheme for this model was known, we also construct a delegation scheme for one-round massively parallel computations, and then apply our lifting theorem to it. - Distributed graph algorithms, using existing distributed delegation schemes (also known as locally verifiable distributed SNARGs). Here, in order to use our lifting theorem we have to first make some observations about the verification procedure of these existing schemes. At the heart of this work is a new abstraction, updatable batch arguments for NP (UpBARGs), which we define and construct. Standard BARGs allow one to prove a batch of k NP-statements using a proof whose length barely grows with k; however, the statements and their witnesses must all be known in advance. In contrast, UpBARGs support adding statements and witnesses on the fly, making them a flexible tool for constructing IVC across different computational models.

Cite as

Eden Aldema Tshuva and Rotem Oshman. Model-Generic Incrementally Verifiable Computation from Updatable BARGs. In 17th Innovations in Theoretical Computer Science Conference (ITCS 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 362, pp. 6:1-6:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{aldematshuva_et_al:LIPIcs.ITCS.2026.6,
  author =	{Aldema Tshuva, Eden and Oshman, Rotem},
  title =	{{Model-Generic Incrementally Verifiable Computation from Updatable BARGs}},
  booktitle =	{17th Innovations in Theoretical Computer Science Conference (ITCS 2026)},
  pages =	{6:1--6:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-410-9},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{362},
  editor =	{Saraf, Shubhangi},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2026.6},
  URN =		{urn:nbn:de:0030-drops-252931},
  doi =		{10.4230/LIPIcs.ITCS.2026.6},
  annote =	{Keywords: incrementally verifiable computation, massively parallel computation, streaming, parallel RAM, batch arguments, SNARG}
}

Document

DOI: 10.4230/LIPIcs.ITCS.2026.116

Decentralized Data Archival: New Definitions and Constructions

Authors: Elaine Shi, Rose Silver, and Changrui Mu

Published in: LIPIcs, Volume 362, 17th Innovations in Theoretical Computer Science Conference (ITCS 2026)

Abstract

We initiate the study of a new abstraction called incremental decentralized data archival (iDDA). Specifically, imagine that there is an ever-growing, massive database such as a blockchain, a comprehensive human knowledge base like Wikipedia, or the Internet archive. We want to build a decentralized archival system for such datasets to ensure long-term robustness and sustainability. We identify several important properties that an iDDA scheme should satisfy. First, to promote heterogeneity and decentralization, we want to encourage even weak nodes with limited space (e.g., users' home computers) to contribute. The minimum space requirement to contribute should be approximately independent of the data size. Second, if a collection of nodes together receive rewards commensurate with contributing a total of m blocks of space, then we want the following reassurances: 1) if m is at least the database size, we should be able to reconstruct the entire dataset; and 2) these nodes should actually be committing roughly m space in aggregate - specifically, when m is much larger than the data size, these nodes cannot store only one copy of the database, and be able to impersonate arbitrarily many pseudonyms and get unbounded rewards. We propose new definitions that mathematically formalize the aforementioned requirements of an iDDA scheme. We also devise an efficient construction in the random oracle model which satisfies the desired security requirements. Our scheme incurs only Õ(1) audit cost, as well as Õ(1) update cost for both the publisher and each node, where Õ(⋅) hides polylogarithmic factors. Further, the minimum space provisioning required to contribute is as small as polylogarithmic. Our construction exposes several interesting technical challenges. Specifically, we show that a straightforward application of the standard hierarchical data structure fails, since both our security definition and the underlying cryptographic primitives we employ lack the desired compositional guarantees. We devise novel techniques to overcome these compositional issues, resulting in a construction with provable security while still retaining efficiency. Finally, our new definitions also make a conceptual contribution, and lay the theoretical groundwork for the study of iDDA. We raise several interesting open problems along this direction.

Cite as

Elaine Shi, Rose Silver, and Changrui Mu. Decentralized Data Archival: New Definitions and Constructions. In 17th Innovations in Theoretical Computer Science Conference (ITCS 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 362, pp. 116:1-116:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{shi_et_al:LIPIcs.ITCS.2026.116,
  author =	{Shi, Elaine and Silver, Rose and Mu, Changrui},
  title =	{{Decentralized Data Archival: New Definitions and Constructions}},
  booktitle =	{17th Innovations in Theoretical Computer Science Conference (ITCS 2026)},
  pages =	{116:1--116:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-410-9},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{362},
  editor =	{Saraf, Shubhangi},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2026.116},
  URN =		{urn:nbn:de:0030-drops-254037},
  doi =		{10.4230/LIPIcs.ITCS.2026.116},
  annote =	{Keywords: Decentralized Data Archival}
}

Document

DOI: 10.4230/LIPIcs.ITCS.2026.18

Interactive Proofs for Distribution Testing with Conditional Oracles

Authors: Ari Biswas, Mark Bun, Clément L. Canonne, and Satchit Sivakumar

Published in: LIPIcs, Volume 362, 17th Innovations in Theoretical Computer Science Conference (ITCS 2026)

Abstract

We revisit the framework of interactive proofs for distribution testing, first introduced by Chiesa and Gur (ITCS 2018), which has recently experienced a surge in interest, accompanied by notable progress (e.g., Herman and Rothblum, STOC 2022, FOCS 2023; Herman, RANDOM 2024). In this model, a data-poor verifier determines whether a probability distribution has a property of interest by interacting with an all-powerful, data-rich but untrusted prover bent on convincing them that it has the property. While prior work gave sample-, time-, and communication-efficient protocols for testing and estimating a range of distribution properties, they all suffer from an inherent issue: for most interesting properties of distributions over a domain of size N, the verifier must draw at least Ω(√N) samples of its own. While sublinear in N, this is still prohibitive for large domains encountered in practice. In this work, we circumvent this limitation by augmenting the verifier with the ability to perform an exponentially smaller number of more powerful (but reasonable) pairwise conditional queries, effectively enabling them to perform "local comparison checks" of the prover’s claims. We systematically investigate the landscape of interactive proofs in this new setting, giving poly-logarithmic query and sample protocols for (tolerantly) testing all label-invariant properties, thus demonstrating exponential savings without compromising on communication, for this large and fundamental class of testing tasks.

Cite as

Ari Biswas, Mark Bun, Clément L. Canonne, and Satchit Sivakumar. Interactive Proofs for Distribution Testing with Conditional Oracles. In 17th Innovations in Theoretical Computer Science Conference (ITCS 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 362, pp. 18:1-18:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{biswas_et_al:LIPIcs.ITCS.2026.18,
  author =	{Biswas, Ari and Bun, Mark and Canonne, Cl\'{e}ment L. and Sivakumar, Satchit},
  title =	{{Interactive Proofs for Distribution Testing with Conditional Oracles}},
  booktitle =	{17th Innovations in Theoretical Computer Science Conference (ITCS 2026)},
  pages =	{18:1--18:13},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-410-9},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{362},
  editor =	{Saraf, Shubhangi},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2026.18},
  URN =		{urn:nbn:de:0030-drops-253059},
  doi =		{10.4230/LIPIcs.ITCS.2026.18},
  annote =	{Keywords: Distribution Testing, Interactive Proofs}
}

Document

DOI: 10.4230/LIPIcs.OPODIS.2025.6

Foundations of Fiat-Denominated Loans Collateralized by Cryptocurrencies

Authors: Pavel Hubáček, Jan Václavek, and Michelle Yeo

Published in: LIPIcs, Volume 361, 29th International Conference on Principles of Distributed Systems (OPODIS 2025)

Abstract

The rising importance of cryptocurrencies as financial assets pushed their applicability from an object of speculation closer to standard financial instruments such as loans. In this work, we initiate the study of secure protocols that enable fiat-denominated loans collateralized by cryptocurrencies such as Bitcoin. We provide limited-custodial protocols for such loans relying only on trusted arbitration and provide their game-theoretical analysis. We also highlight various interesting directions for future research.

Cite as

Pavel Hubáček, Jan Václavek, and Michelle Yeo. Foundations of Fiat-Denominated Loans Collateralized by Cryptocurrencies. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 6:1-6:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{hubacek_et_al:LIPIcs.OPODIS.2025.6,
  author =	{Hub\'{a}\v{c}ek, Pavel and V\'{a}clavek, Jan and Yeo, Michelle},
  title =	{{Foundations of Fiat-Denominated Loans Collateralized by Cryptocurrencies}},
  booktitle =	{29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
  pages =	{6:1--6:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-409-3},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{361},
  editor =	{Arusoaie, Andrei and Onica, Emanuel and Spear, Michael and Tucci-Piergiovanni, Sara},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2025.6},
  URN =		{urn:nbn:de:0030-drops-251796},
  doi =		{10.4230/LIPIcs.OPODIS.2025.6},
  annote =	{Keywords: Blockchains, Cryptocurrencies, DeFi, Loans, Mechanism design, Subgame Perfect Equilibrium, Rational analysis}
}

Document

Brief Announcement

DOI: 10.4230/LIPIcs.DISC.2025.44

Brief Announcement: Incrementally Verifiable Distributed Computation

Authors: Eden Aldema Tshuva and Rotem Oshman

Published in: LIPIcs, Volume 356, 39th International Symposium on Distributed Computing (DISC 2025)

Abstract

Incrementally verifiable computation (IVC) is a cryptographic scheme that allows a prover to certify the correctness of a long or ongoing computation in an incremental manner, by repeatedly updating a proof certifying the computation so far. Updating the proof does not require access to the entire trace of the computation, which makes the IVC prover memory efficient. In this work we construct incrementally verifiable distributed computation, which allows a distributed algorithm to efficiently certify its own execution using low memory and communication overhead. Our primary motivation is massively-parallel computation (MPC), where memory efficiency is make-or-break: the machines participating in an MPC algorithm usually cannot store the entire trace of their computation. Thus, certifying MPC algorithms essentially requires distributed IVC. At the heart of this work is a new abstraction, updatable batch arguments for {NP} (UpBARGs), which we define and construct. Standard BARGs allow one to prove a batch of k {NP}-statements using a proof whose length barely grows with k; however, the statements and their witnesses must all be known in advance. In contrast, UpBARGs support adding statements and witnesses on the fly, making them a flexible tool for constructing IVC across different computational models. We use UpBARGs to construct IVC for streaming algorithms, for MPC algorithms, and for PRAM algorithms in the exclusive-read exclusive-write (EREW) model.

Cite as

Eden Aldema Tshuva and Rotem Oshman. Brief Announcement: Incrementally Verifiable Distributed Computation. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 44:1-44:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{aldematshuva_et_al:LIPIcs.DISC.2025.44,
  author =	{Aldema Tshuva, Eden and Oshman, Rotem},
  title =	{{Brief Announcement: Incrementally Verifiable Distributed Computation}},
  booktitle =	{39th International Symposium on Distributed Computing (DISC 2025)},
  pages =	{44:1--44:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-402-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{356},
  editor =	{Kowalski, Dariusz R.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.44},
  URN =		{urn:nbn:de:0030-drops-248829},
  doi =		{10.4230/LIPIcs.DISC.2025.44},
  annote =	{Keywords: Incrementally verifiable computation, massively parallel computation, streaming, parallel RAM, batch arguments, SNARG}
}

Document

DOI: 10.4230/LIPIcs.AFT.2025.3

Fast, Private and Regulated Payments in Asynchronous Networks

Authors: Maxence Brugeres, Victor Languille, Petr Kuznetsov, and Hamza Zarfaoui

Published in: LIPIcs, Volume 354, 7th Conference on Advances in Financial Technologies (AFT 2025)

Abstract

We propose a decentralized asset-transfer system that enjoys full privacy: no party can learn the details of a transaction, except for its issuer and its recipient. Furthermore, the recipient is not aware of the sender’s identity. Our system does not rely on consensus or synchrony assumptions, and therefore, it is responsive, since it runs at the actual network speed. Under the hood, every transaction creates a consumable coin equipped with a non-interactive zero-knowledge proof (NIZK) that confirms that the issuer has sufficient funds without revealing any information about her identity, the recipient’s identity, or the payment amount. Moreover, we equip our system with a regulatory enforcement mechanism that can be used to regulate transfer limits or restrict specific addresses from sending or receiving funds, while preserving the system’s privacy guarantees. Finally, we report on PaxPay, our implementation of Fully Private Asset Transfer (FPAT) that uses the Gnark library for the NIZKs. In our benchmark, PaxPay exhibits better performance than earlier proposals that either ensure only partial privacy, require some kind of network synchrony or do not implement regulation features. Our system thus reconciles privacy, responsiveness, regulation enforcement and performance.

Cite as

Maxence Brugeres, Victor Languille, Petr Kuznetsov, and Hamza Zarfaoui. Fast, Private and Regulated Payments in Asynchronous Networks. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 3:1-3:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{brugeres_et_al:LIPIcs.AFT.2025.3,
  author =	{Brugeres, Maxence and Languille, Victor and Kuznetsov, Petr and Zarfaoui, Hamza},
  title =	{{Fast, Private and Regulated Payments in Asynchronous Networks}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{3:1--3:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-400-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{354},
  editor =	{Avarikioti, Zeta and Christin, Nicolas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2025.3},
  URN =		{urn:nbn:de:0030-drops-247227},
  doi =		{10.4230/LIPIcs.AFT.2025.3},
  annote =	{Keywords: Anonymous, Asset Transfer, Asynchronous System, BFT, CBDC, NIZK, Payment System, Privacy, Regulation, Scalability, zk-SNARK}
}

Document

DOI: 10.4230/LIPIcs.AFT.2025.1

Cache Timing Leakages in Zero-Knowledge Protocols

Authors: Shibam Mukherjee, Christian Rechberger, and Markus Schofnegger

Published in: LIPIcs, Volume 354, 7th Conference on Advances in Financial Technologies (AFT 2025)

Abstract

The area of modern zero-knowledge proof systems has seen a significant rise in popularity over the last couple of years, with new techniques and optimized constructions emerging on a regular basis. As the field matures, the aspect of implementation attacks becomes more relevant, however side-channel attacks on zero-knowledge proof systems have seen surprisingly little treatment so far. In this paper, we give an overview of potential attack vectors and show that some of the underlying finite field libraries, and implementations of heavily used components like hash functions using them, are vulnerable w.r.t. cache attacks on CPUs. On the positive side, we demonstrate that the computational overhead to protect against these attacks is relatively small.

Cite as

Shibam Mukherjee, Christian Rechberger, and Markus Schofnegger. Cache Timing Leakages in Zero-Knowledge Protocols. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 1:1-1:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{mukherjee_et_al:LIPIcs.AFT.2025.1,
  author =	{Mukherjee, Shibam and Rechberger, Christian and Schofnegger, Markus},
  title =	{{Cache Timing Leakages in Zero-Knowledge Protocols}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{1:1--1:26},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-400-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{354},
  editor =	{Avarikioti, Zeta and Christin, Nicolas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2025.1},
  URN =		{urn:nbn:de:0030-drops-247201},
  doi =		{10.4230/LIPIcs.AFT.2025.1},
  annote =	{Keywords: zero-knowledge, protocol, cache timing, side-channel, leakage}
}

Document

DOI: 10.4230/LIPIcs.AFT.2025.2

Zero-Knowledge Authenticator for Blockchain: Policy-Private and Obliviously Updateable

Authors: Kostas Kryptos Chalkias, Deepak Maram, Arnab Roy, Joy Wang, and Aayush Yadav

Published in: LIPIcs, Volume 354, 7th Conference on Advances in Financial Technologies (AFT 2025)

Abstract

Transaction details and participant identities on the blockchain are often publicly exposed. In this work, we posit that blockchain’s transparency should not come at the cost of privacy. To that end, we introduce zero-knowledge authenticators (zkAt), a new cryptographic primitive for privacy-preserving authentication on public blockchains. zkAt utilizes zero-knowledge proofs to enable users to authenticate transactions, while keeping the underlying authentication policies private. Prior solutions for such policy-private authentication required the use of threshold signatures, which can only hide the threshold access structure itself. In comparison, zkAt provides privacy for arbitrarily complex authentication policies, and offers a richer interface even within the threshold access structure by, for instance, allowing for the combination of signatures under distinct signature schemes. In order to construct zkAt, we design a compiler that transforms the popular Groth16 non-interactive zero knowledge (NIZK) proof system into a NIZK with equivocable verification keys, a property that we define in this work. Then, for any zkAt constructed using proof systems with this new property, we show that all public information must be independent of the policy, thereby achieving policy-privacy. Next, we give an extension of zkAt, called zkAt^+ wherein, assuming a trusted authority, policies can be updated obliviously in the sense that a third-party learns no new information when a policy is updated by the policy issuer. We also give a theoretical construction for zkAt^+ using recursive NIZKs, and explore the integration of zkAt into modern blockchains. Finally, to evaluate their feasibility, we implement both our schemes for a specific threshold access structure. Our findings show that zkAt achieves comparable performance to traditional threshold signatures, while also attaining privacy for significantly more complex policies with very little overhead.

Cite as

Kostas Kryptos Chalkias, Deepak Maram, Arnab Roy, Joy Wang, and Aayush Yadav. Zero-Knowledge Authenticator for Blockchain: Policy-Private and Obliviously Updateable. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 2:1-2:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{kryptoschalkias_et_al:LIPIcs.AFT.2025.2,
  author =	{Kryptos Chalkias, Kostas and Maram, Deepak and Roy, Arnab and Wang, Joy and Yadav, Aayush},
  title =	{{Zero-Knowledge Authenticator for Blockchain: Policy-Private and Obliviously Updateable}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{2:1--2:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-400-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{354},
  editor =	{Avarikioti, Zeta and Christin, Nicolas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2025.2},
  URN =		{urn:nbn:de:0030-drops-247218},
  doi =		{10.4230/LIPIcs.AFT.2025.2},
  annote =	{Keywords: Blockchain privacy, authentication schemes, threshold wallets, zero knowledge proofs}
}

Document

DOI: 10.4230/LIPIcs.AFT.2025.31

Trustless Bridges via Random Sampling Light Clients

Authors: Bhargav Nagaraja Bhatt, Fatemeh Shirazi, and Alistair Stewart

Published in: LIPIcs, Volume 354, 7th Conference on Advances in Financial Technologies (AFT 2025)

Abstract

The increasing number of blockchain projects introduced annually has led to a pressing need for secure and efficient interoperability solutions. Currently, the lack of such solutions forces end-users to rely on centralized intermediaries, contradicting the core principle of decentralization and trust minimization in blockchain technology. We propose a decentralized and efficient interoperability solution (aka Bridge Protocol) that operates without additional trust assumptions, relying solely on the Byzantine Fault Tolerance (BFT) properties of the two chains being connected. In particular, relayers (actors that exchange messages between networks) are permissionless and decentralized, hence eliminating any single point of failure. We introduce Random Sampling, a novel technique for on-chain light clients to efficiently follow the history of PoS blockchains by reducing the signature verifications required. Here, the randomness is drawn on-chain, for example, using Ethereum’s RANDAO. We analyze the security of the bridge from a crypto- economic perspective and provide a framework to derive the security parameters. This includes handling subtle concurrency issues and randomness bias in strawman designs. While the protocol is applicable to various PoS chains, we demonstrate the protocol’s practical feasibility by showcasing an instantiated bridge between Polkadot and Ethereum (currently deployed), and discuss some practical security challenges. Furthermore, we evaluate the efficiency of our on-chain light client verifier (implemented as an Ethereum smart contract) against SNARK-based approaches, demonstrating significantly lower gas costs for signature verification - even for validator sets up to 10⁶.

Cite as

Bhargav Nagaraja Bhatt, Fatemeh Shirazi, and Alistair Stewart. Trustless Bridges via Random Sampling Light Clients. In 7th Conference on Advances in Financial Technologies (AFT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 354, pp. 31:1-31:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{bhatt_et_al:LIPIcs.AFT.2025.31,
  author =	{Bhatt, Bhargav Nagaraja and Shirazi, Fatemeh and Stewart, Alistair},
  title =	{{Trustless Bridges via Random Sampling Light Clients}},
  booktitle =	{7th Conference on Advances in Financial Technologies (AFT 2025)},
  pages =	{31:1--31:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-400-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{354},
  editor =	{Avarikioti, Zeta and Christin, Nicolas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AFT.2025.31},
  URN =		{urn:nbn:de:0030-drops-247503},
  doi =		{10.4230/LIPIcs.AFT.2025.31},
  annote =	{Keywords: PoS Blockchains, Trustless Bridges, Light Clients, Decentralised Relayers, RANDAO Bias}
}

Document

DOI: 10.4230/LIPIcs.ITC.2025.1

Amortized Locally Decodable Codes for Insertions and Deletions

Authors: Jeremiah Blocki and Justin Zhang

Published in: LIPIcs, Volume 343, 6th Conference on Information-Theoretic Cryptography (ITC 2025)

Abstract

Locally Decodable Codes (LDCs) are error correcting codes which permit the recovery of any single message symbol with a low number of queries to the codeword (the locality). Traditional LDC tradeoffs between the rate, locality, and error tolerance are undesirable even in relaxed settings where the encoder/decoder share randomness or where the channel is resource-bounded. Recent work by Blocki and Zhang initiated the study of Hamming amortized Locally Decodable Codes (aLDCs), which allow the local decoder to amortize their number of queries over the recovery of a small subset of message symbols. Surprisingly, Blocki and Zhang construct asymptotically ideal (constant rate, constant amortized locality, and constant error tolerance) Hamming aLDCs in private-key and resource-bounded settings. While this result overcame previous barriers and impossibility results for Hamming LDCs, it is not clear whether the techniques extend to Insdel LDCs. Constructing Insdel LDCs which are resilient to insertion and/or deletion errors is known to be even more challenging. For example, Gupta (STOC'24) proved that no Insdel LDC with constant rate and error tolerance exists even in relaxed settings. Our first contribution is to provide a Hamming-to-Insdel compiler which transforms any amortized Hamming LDC that satisfies a particular property (consecutive interval querying) to amortized Insdel LDC while asymptotically preserving the rate, error tolerance and amortized locality. Prior Hamming-to-Insdel compilers of Ostrovsky and Paskin-Cherniavsky (ICITS'15) and Block et al. (FSTTCS'20) worked for arbitrary Hamming LDCs, but incurred an undesirable polylogarithmic blow-up in the locality. Our second contribution is a construction of an ideal amortized Hamming LDC which satisfies our special property (consecutive interval querying) in the relaxed settings where the sender/receiver share randomness or where the channel is resource bounded. Taken together, we obtain ideal Insdel aLDCs in private-key and resource-bounded settings with constant amortized locality, constant rate and constant error tolerance. This result is surprising in light of Gupta’s (STOC'24) impossibility result which demonstrates a strong separation between locality and amortized locality for Insdel LDCs.

Cite as

Jeremiah Blocki and Justin Zhang. Amortized Locally Decodable Codes for Insertions and Deletions. In 6th Conference on Information-Theoretic Cryptography (ITC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 343, pp. 1:1-1:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{blocki_et_al:LIPIcs.ITC.2025.1,
  author =	{Blocki, Jeremiah and Zhang, Justin},
  title =	{{Amortized Locally Decodable Codes for Insertions and Deletions}},
  booktitle =	{6th Conference on Information-Theoretic Cryptography (ITC 2025)},
  pages =	{1:1--1:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-385-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{343},
  editor =	{Gilboa, Niv},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITC.2025.1},
  URN =		{urn:nbn:de:0030-drops-243518},
  doi =		{10.4230/LIPIcs.ITC.2025.1},
  annote =	{Keywords: Amortized Locally Decodable Codes, Insertion and Deletion Errors}
}

Document

DOI: 10.4230/LIPIcs.CCC.2025.31

Towards Free Lunch Derandomization from Necessary Assumptions (And OWFs)

Authors: Marshall Ball, Lijie Chen, and Roei Tell

Published in: LIPIcs, Volume 339, 40th Computational Complexity Conference (CCC 2025)

Abstract

The question of optimal derandomization, introduced by Doron et. al (JACM 2022), garnered significant recent attention. Works in recent years showed conditional superfast derandomization algorithms, as well as conditional impossibility results, and barriers for obtaining superfast derandomization using certain black-box techniques. Of particular interest is the extreme high-end, which focuses on "free lunch" derandomization, as suggested by Chen and Tell (FOCS 2021). This is derandomization that incurs essentially no time overhead, and errs only on inputs that are infeasible to find. Constructing such algorithms is challenging, and so far there have not been any results following the one in their initial work. In their result, their algorithm is essentially the classical Nisan-Wigderson generator, and they relied on an ad-hoc assumption asserting the existence of a function that is non-batch-computable over all polynomial-time samplable distributions. In this work we deduce free lunch derandomization from a variety of natural hardness assumptions. In particular, we do not resort to non-batch-computability, and the common denominator for all of our assumptions is hardness over all polynomial-time samplable distributions, which is necessary for the conclusion. The main technical components in our proofs are constructions of new and superfast targeted generators, which completely eliminate the time overheads that are inherent to all previously known constructions. In particular, we present an alternative construction for the targeted generator by Chen and Tell (FOCS 2021), which is faster than the original construction, and also more natural and technically intuitive. These contributions significantly strengthen the evidence for the possibility of free lunch derandomization, distill the required assumptions for such a result, and provide the first set of dedicated technical tools that are useful for studying the question.

Cite as

Marshall Ball, Lijie Chen, and Roei Tell. Towards Free Lunch Derandomization from Necessary Assumptions (And OWFs). In 40th Computational Complexity Conference (CCC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 339, pp. 31:1-31:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{ball_et_al:LIPIcs.CCC.2025.31,
  author =	{Ball, Marshall and Chen, Lijie and Tell, Roei},
  title =	{{Towards Free Lunch Derandomization from Necessary Assumptions (And OWFs)}},
  booktitle =	{40th Computational Complexity Conference (CCC 2025)},
  pages =	{31:1--31:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-379-9},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{339},
  editor =	{Srinivasan, Srikanth},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CCC.2025.31},
  URN =		{urn:nbn:de:0030-drops-237259},
  doi =		{10.4230/LIPIcs.CCC.2025.31},
  annote =	{Keywords: Pseudorandomness, Derandomization}
}

Document

Track A: Algorithms, Complexity and Games

DOI: 10.4230/LIPIcs.ICALP.2025.56

Boosting SNARKs and Rate-1 Barrier in Arguments of Knowledge

Authors: Jiaqi Cheng and Rishab Goyal

Published in: LIPIcs, Volume 334, 52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025)

Abstract

We design a generic compiler to boost any non-trivial succinct non-interactive argument of knowledge (SNARK) to full succinctness. Our results come in two flavors: 1) For any constant ε > 0, any SNARK with proof size |π| < |ω|/(λ^ε) + poly(λ, |x|) can be upgraded to a fully succinct SNARK, where all system parameters (such as proof/CRS sizes and setup/verifier run-times) grow as fixed polynomials in λ, independent of witness size. 2) Under an additional assumption that the underlying SNARK has as an efficient knowledge extractor, we further improve our result to upgrade any non-trivial SNARK. For example, we show how to design fully succinct SNARKs from SNARKs with proofs of length |ω| - Ω(λ), or |ω|/(1+ε) + poly(λ, |x|), any constant ε > 0. Our result reduces the long-standing challenge of designing fully succinct SNARKs to designing arguments of knowledge that beat the trivial construction. It also establishes optimality of rate-1 arguments of knowledge (such as NIZKs [Gentry-Groth-Ishai-Peikert-Sahai-Smith; JoC'15] and BARGs [Devadas-Goyal-Kalai-Vaikuntanathan, Paneth-Pass; FOCS'22]), and suggests any further improvement is tantamount to designing fully succinct SNARKs, thus requires bypassing established black-box barriers [Gentry-Wichs; STOC'11].

Cite as

Jiaqi Cheng and Rishab Goyal. Boosting SNARKs and Rate-1 Barrier in Arguments of Knowledge. In 52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 334, pp. 56:1-56:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{cheng_et_al:LIPIcs.ICALP.2025.56,
  author =	{Cheng, Jiaqi and Goyal, Rishab},
  title =	{{Boosting SNARKs and Rate-1 Barrier in Arguments of Knowledge}},
  booktitle =	{52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025)},
  pages =	{56:1--56:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-372-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{334},
  editor =	{Censor-Hillel, Keren and Grandoni, Fabrizio and Ouaknine, Jo\"{e}l and Puppis, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2025.56},
  URN =		{urn:nbn:de:0030-drops-234339},
  doi =		{10.4230/LIPIcs.ICALP.2025.56},
  annote =	{Keywords: SNARGs, RAM Delegation}
}

Document

DOI: 10.4230/LIPIcs.ITCS.2025.6

Doubly Sub-Linear Interactive Proofs of Proximity

Authors: Noga Amir, Oded Goldreich, and Guy N. Rothblum

Published in: LIPIcs, Volume 325, 16th Innovations in Theoretical Computer Science Conference (ITCS 2025)

Abstract

We initiate a study of doubly-efficient interactive proofs of proximity, while focusing on properties that can be tested within query-complexity that is significantly sub-linear, and seeking interactive proofs of proximity in which 1) The query-complexity of verification is significantly smaller than the query-complexity of testing. 2) The query-complexity of the honest prover strategy is not much larger than the query-complexity of testing. We call such proof systems doubly-sublinear IPPs (dsIPPs). We present a few doubly-sublinear IPPs. A salient feature of these IPPs is that the honest prover does not employ an optimal strategy (i.e. a strategy that maximizes the verifier’s acceptance probability). In particular, the honest prover in our IPP for sets recognizable by constant-width read-once oblivious branching programs uses a distance-approximator for such sets.

Cite as

Noga Amir, Oded Goldreich, and Guy N. Rothblum. Doubly Sub-Linear Interactive Proofs of Proximity. In 16th Innovations in Theoretical Computer Science Conference (ITCS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 325, pp. 6:1-6:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{amir_et_al:LIPIcs.ITCS.2025.6,
  author =	{Amir, Noga and Goldreich, Oded and Rothblum, Guy N.},
  title =	{{Doubly Sub-Linear Interactive Proofs of Proximity}},
  booktitle =	{16th Innovations in Theoretical Computer Science Conference (ITCS 2025)},
  pages =	{6:1--6:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-361-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{325},
  editor =	{Meka, Raghu},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2025.6},
  URN =		{urn:nbn:de:0030-drops-226345},
  doi =		{10.4230/LIPIcs.ITCS.2025.6},
  annote =	{Keywords: Interactive Proof Systems, Interactive Proofs of Proximity, Query Complexity, Read Once Branching Programs, Sub-linear}
}

Document

DOI: 10.4230/LIPIcs.ITCS.2025.23

Accumulation Without Homomorphism

Authors: Benedikt Bünz, Pratyush Mishra, Wilson Nguyen, and William Wang

Published in: LIPIcs, Volume 325, 16th Innovations in Theoretical Computer Science Conference (ITCS 2025)

Abstract

Accumulation schemes are a simple yet powerful primitive that enable highly efficient constructions of incrementally verifiable computation (IVC). Unfortunately, all prior accumulation schemes rely on homomorphic vector commitments whose security is based on public-key assumptions. It is an interesting open question to construct efficient accumulation schemes that avoid the need for such assumptions. In this paper, we answer this question affirmatively by constructing an accumulation scheme from non-homomorphic vector commitments which can be realized from solely symmetric-key assumptions (e.g., Merkle trees). We overcome the need for homomorphisms by instead performing spot-checks over error-correcting encodings of the committed vectors. Unlike prior accumulation schemes, our scheme only supports a bounded number of accumulation steps. We show that such bounded-depth accumulation still suffices to construct proof-carrying data (a generalization of IVC). We also demonstrate several optimizations to our PCD construction which greatly improve concrete efficiency.

Cite as

Benedikt Bünz, Pratyush Mishra, Wilson Nguyen, and William Wang. Accumulation Without Homomorphism. In 16th Innovations in Theoretical Computer Science Conference (ITCS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 325, pp. 23:1-23:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{bunz_et_al:LIPIcs.ITCS.2025.23,
  author =	{B\"{u}nz, Benedikt and Mishra, Pratyush and Nguyen, Wilson and Wang, William},
  title =	{{Accumulation Without Homomorphism}},
  booktitle =	{16th Innovations in Theoretical Computer Science Conference (ITCS 2025)},
  pages =	{23:1--23:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-361-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{325},
  editor =	{Meka, Raghu},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2025.23},
  URN =		{urn:nbn:de:0030-drops-226510},
  doi =		{10.4230/LIPIcs.ITCS.2025.23},
  annote =	{Keywords: Proof-carrying data, incrementally verifiable computation, accumulation schemes}
}

Document

DOI: 10.4230/LIPIcs.ITCS.2025.8

Single-Round Proofs of Quantumness from Knowledge Assumptions

Authors: Petia Arabadjieva, Alexandru Gheorghiu, Victor Gitton, and Tony Metger

Published in: LIPIcs, Volume 325, 16th Innovations in Theoretical Computer Science Conference (ITCS 2025)

Abstract

A proof of quantumness is an efficiently verifiable interactive test that an efficient quantum computer can pass, but all efficient classical computers cannot (under some cryptographic assumption). Such protocols play a crucial role in the certification of quantum devices. Existing single-round protocols based solely on a cryptographic hardness assumption (like asking the quantum computer to factor a large number) require large quantum circuits, whereas multi-round ones use smaller circuits but require experimentally challenging mid-circuit measurements. In this work, we construct efficient single-round proofs of quantumness based on existing knowledge assumptions. While knowledge assumptions have not been previously considered in this context, we show that they provide a natural basis for separating classical and quantum computation. Our work also helps in understanding the interplay between black-box/white-box reductions and cryptographic assumptions in the design of proofs of quantumness. Specifically, we show that multi-round protocols based on Decisional Diffie-Hellman (DDH) or Learning With Errors (LWE) can be "compiled" into single-round protocols using a knowledge-of-exponent assumption [Bitansky et al., 2012] or knowledge-of-lattice-point assumption [Loftus et al., 2012], respectively. We also prove an adaptive hardcore-bit statement for a family of claw-free functions based on DDH, which might be of independent interest.

Cite as

Petia Arabadjieva, Alexandru Gheorghiu, Victor Gitton, and Tony Metger. Single-Round Proofs of Quantumness from Knowledge Assumptions. In 16th Innovations in Theoretical Computer Science Conference (ITCS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 325, pp. 8:1-8:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{arabadjieva_et_al:LIPIcs.ITCS.2025.8,
  author =	{Arabadjieva, Petia and Gheorghiu, Alexandru and Gitton, Victor and Metger, Tony},
  title =	{{Single-Round Proofs of Quantumness from Knowledge Assumptions}},
  booktitle =	{16th Innovations in Theoretical Computer Science Conference (ITCS 2025)},
  pages =	{8:1--8:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-361-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{325},
  editor =	{Meka, Raghu},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2025.8},
  URN =		{urn:nbn:de:0030-drops-226364},
  doi =		{10.4230/LIPIcs.ITCS.2025.8},
  annote =	{Keywords: Proofs of quantumness, Knowledge assumptions, Learning with errors, Decisional Diffie-Hellman}
}

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