## CryptoDB

### Alessandro Chiesa

#### Publications

**Year**

**Venue**

**Title**

2021

CRYPTO

Subquadratic SNARGs in the Random Oracle Model
📺
Abstract

In a seminal work, Micali (FOCS 1994) gave the first succinct non-interactive argument (SNARG) in the random oracle model (ROM). The construction combines a PCP and a cryptographic commitment, and has several attractive features: it is plausibly post-quantum; it can be heuristically instantiated via lightweight cryptography; and it has a transparent (public-coin) parameter setup. However, it also has a significant drawback: a large argument size.
In this work, we provide a new construction that achieves a smaller argument size. This is the first progress on the Micali construction since it was introduced over 25 years ago.
A SNARG in the ROM is (t,ε)-secure if every t-query malicious prover can convince the verifier of a false statement with probability at most ε. For (t,ε)-security, the argument size of all known SNARGs in the ROM (including Micali's) is Õ((log (t/ε))^2) bits, *even* if one were to rely on conjectured probabilistic proofs well beyond current techniques. In practice, these costs lead to SNARGs that are much larger than constructions based on other (pre-quantum and costly) tools. This has led many to believe that SNARGs in the ROM are inherently quadratic.
We show that this is not the case. We present a SNARG in the ROM with a sub-quadratic argument size: Õ(log (t/ε) * log t). Our construction relies on a strong soundness notion for PCPs and a weak binding notion for commitments. We hope that our work paves the way for understanding if a linear argument size, that is O(log (t/ε)), is achievable in the ROM.

2021

CRYPTO

Sumcheck Arguments and their Applications
📺
Abstract

We introduce a class of interactive protocols, which we call *sumcheck arguments*, that establishes a novel connection between the sumcheck protocol (Lund et al. JACM 1992) and folding techniques for Pedersen commitments (Bootle et al. EUROCRYPT 2016).
Informally, we consider a general notion of bilinear commitment over modules, and show that the sumcheck protocol applied to a certain polynomial associated with the commitment scheme yields a succinct argument of knowledge for openings of the commitment. Building on this, we additionally obtain succinct arguments for the NP-complete language R1CS over certain rings.
Sumcheck arguments enable us to recover as a special case numerous prior works in disparate cryptographic settings (such as discrete logarithms, pairings, RSA groups, lattices), providing one abstract framework to understand them all. Further, we answer open questions raised in prior works, such as obtaining a lattice-based succinct argument from the SIS assumption for satisfiability problems over rings.

2021

CRYPTO

Proof-Carrying Data without Succinct Arguments
📺
Abstract

Proof-carrying data (PCD) is a powerful cryptographic primitive that enables mutually distrustful parties to perform distributed computations that run indefinitely. Known approaches to construct PCD are based on succinct non-interactive arguments of knowledge (SNARKs) that have a succinct verifier or a succinct accumulation scheme.
In this paper we show how to obtain PCD without relying on SNARKs. We construct a PCD scheme given any non-interactive argument of knowledge (e.g., with linear-size arguments) that has a *split accumulation scheme*, which is a weak form of accumulation that we introduce.
Moreover, we construct a transparent non-interactive argument of knowledge for R1CS whose split accumulation is verifiable via a (small) *constant number of group and field operations*. Our construction is proved secure in the random oracle model based on the hardness of discrete logarithms, and it leads, via the random oracle heuristic and our result above, to concrete efficiency improvements for PCD.
Along the way, we construct a split accumulation scheme for Hadamard products under Pedersen commitments and for a simple polynomial commitment scheme based on Pedersen commitments.
Our results are supported by a modular and efficient implementation.

2021

TCC

Tight Security Bounds for Micali’s SNARGs
📺
Abstract

Succinct non-interactive arguments (SNARGs) in the random oracle model (ROM) have several attractive features: they are plausibly post-quantum; they can be heuristically instantiated via lightweight cryptography; and they have a transparent (public-coin) parameter setup.
The canonical construction of a SNARG in the ROM is due to Micali (FOCS 1994), who showed how to use a random oracle to compile any probabilistically checkable proof (PCP) with sufficiently-small soundness error into a corresponding SNARG. Yet, while Micali's construction is a seminal result, it has received little attention in terms of analysis in the past 25 years.
In this paper, we observe that prior analyses of the Micali construction are not tight and then present a new analysis that achieves tight security bounds. Our result enables reducing the random oracle's output size, and obtain corresponding savings in concrete argument size.
Departing from prior work, our approach relies on precisely quantifying the cost for an attacker to find several collisions and inversions in the random oracle, and proving that any PCP with small soundness error withstands attackers that succeed in finding a small number of collisions and inversions in a certain tree-based information-theoretic game.

2020

EUROCRYPT

Marlin: Preprocessing zkSNARKs with Universal and Updatable SRS
📺
Abstract

We present a general methodology to construct preprocessing zkSNARKs where the structured reference string (SRS) is universal and updatable. This exploits a novel application of *holographic* IOPs, a natural generalization of holographic PCPs [Babai et al., STOC 1991].
We use our methodology to obtain a preprocessing zkSNARK where the SRS has linear size and arguments have constant size. Our construction improves on Sonic [Maller et al., CCS 2019], the prior state of the art in this setting, in all efficiency parameters: proving is an order of magnitude faster and verification is twice as fast, even with smaller SRS size and argument size. Our construction is most efficient when instantiated in the algebraic group model (also used by Sonic), but we also demonstrate how to realize it under concrete knowledge assumptions.
The core of our zkSNARK is a new holographic IOP for rank-1 constraint satisfiability (R1CS), which is the first to achieve linear proof length and constant query complexity (among other efficiency features).

2020

EUROCRYPT

Fractal: Post-Quantum and Transparent Recursive Proofs from Holography
📺
Abstract

We present a new methodology to efficiently realize recursive composition of succinct non-interactive arguments of knowledge (SNARKs). Prior to this work, the only known methodology relied on pairing-based SNARKs instantiated on cycles of pairing-friendly elliptic curves, an expensive algebraic object. Our methodology does not rely on any special algebraic objects and, moreover, achieves new desirable properties: it is post-quantum and it is transparent (the setup is public coin).
We exploit the fact that recursive composition is simpler for SNARKs with preprocessing, and the core of our work is obtaining a preprocessing zkSNARK for rank-1 constraint satisfiability (R1CS) that is post-quantum and transparent. We obtain this latter by establishing a connection between holography and preprocessing in the random oracle model, and then constructing a holographic proof for R1CS.
We experimentally validate our methodology, demonstrating feasibility in practice.

2020

TCC

Proof-Carrying Data from Accumulation Schemes
📺
Abstract

Recursive proof composition has been shown to lead to powerful primitives such as incrementally-verifiable computation (IVC) and proof-carrying data (PCD). All existing approaches to recursive composition take a succinct non-interactive argument of knowledge (SNARK) and use it to prove a statement about its own verifier. This technique requires that the verifier run in time sublinear in the size of the statement it is checking, a strong requirement that restricts the class of SNARKs from which PCD can be built. This in turn restricts the efficiency and security properties of the resulting scheme.
Bowe, Grigg, and Hopwood (ePrint 2019/1021) outlined a novel approach to recursive composition, and applied it to a particular SNARK construction which does *not* have a sublinear-time verifier. However, they omit details about this approach and do not prove that it satisfies any security property. Nonetheless, schemes based on their ideas have already been implemented in software.
In this work we present a collection of results that establish the theoretical foundations for a generalization of the above approach. We define an *accumulation scheme* for a non-interactive argument, and show that this suffices to construct PCD, even if the argument itself does not have a sublinear-time verifier. Moreover we give constructions of accumulation schemes for SNARKs, which yield PCD schemes with novel efficiency and security features.

2020

TCC

Linear-Time Arguments with Sublinear Verification from Tensor Codes
📺
Abstract

Minimizing the computational cost of the prover is a central goal in the area of succinct arguments. In particular, it remains a challenging open problem to construct a succinct argument where the prover runs in linear time and the verifier runs in polylogarithmic time.
We make progress towards this goal by presenting a new linear-time probabilistic proof. For any fixed ? > 0, we construct an interactive oracle proof (IOP) that, when used for the satisfiability of an N-gate arithmetic circuit, has a prover that uses O(N) field operations and a verifier that uses O(N^?) field operations. The sublinear verifier time is achieved in the holographic setting for every circuit (the verifier has oracle access to a linear-size encoding of the circuit that is computable in linear time).
When combined with a linear-time collision-resistant hash function, our IOP immediately leads to an argument system where the prover performs O(N) field operations and hash computations, and the verifier performs O(N^?) field operations and hash computations (given a short digest of the N-gate circuit).

2020

TCC

Barriers for Succinct Arguments in the Random Oracle Model
📺
Abstract

We establish barriers on the efficiency of succinct arguments in the random oracle model. We give evidence that, under standard complexity assumptions, there do not exist succinct arguments where the argument verifier makes a small number of queries to the random oracle.
The new barriers follow from new insights into how probabilistic proofs play a fundamental role in constructing succinct arguments in the random oracle model.
*IOPs are necessary for succinctness.*
We prove that any succinct argument in the random oracle model can be transformed into a corresponding interactive oracle proof (IOP). The query complexity of the IOP is related to the succinctness of the argument.
*Algorithms for IOPs.*
We prove that if a language has an IOP with good soundness relative to query complexity, then it can be decided via a fast algorithm with small space complexity.
By combining these results we obtain barriers for a large class of deterministic and non-deterministic languages. For example, a succinct argument for 3SAT with few verifier queries implies an IOP with good parameters, which in turn implies a fast algorithm for 3SAT that contradicts the Exponential-Time Hypothesis.
We additionally present results that shed light on the necessity of several features of probabilistic proofs that are typically used to construct succinct arguments, such as holography and state restoration soundness. Our results collectively provide an explanation for "why" known constructions of succinct arguments have a certain structure.

2019

EUROCRYPT

Aurora: Transparent Succinct Arguments for R1CS
Abstract

We design, implement, and evaluate a zero knowledge succinct non-interactive argument (SNARG) for Rank-1 Constraint Satisfaction (R1CS), a widely-deployed NP language undergoing standardization. Our SNARG has a transparent setup, is plausibly post-quantum secure, and uses lightweight cryptography. A proof attesting to the satisfiability of n constraints has size $$O(\log ^2 n)$$O(log2n); it can be produced with $$O(n \log n)$$O(nlogn) field operations and verified with O(n). At 128 bits of security, proofs are less than $${250}\,\mathrm{kB}$$250kB even for several million constraints, more than $$10{\times }$$10× shorter than prior SNARGs 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 $$\texttt {libiop}$$libiop, a 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, and plan to open-source it.

2019

TCC

Succinct Arguments in the Quantum Random Oracle Model
Abstract

Succinct non-interactive arguments (SNARGs) are highly efficient certificates of membership in non-deterministic languages. Constructions of SNARGs in the random oracle model are widely believed to be post-quantum secure, provided the oracle is instantiated with a suitable post-quantum hash function. No formal evidence, however, supports this belief.In this work we provide the first such evidence by proving that the SNARG construction of Micali is unconditionally secure in the quantum random oracle model. We also prove that, analogously to the classical case, the SNARG inherits the zero knowledge and proof of knowledge properties of the PCP underlying the Micali construction. We thus obtain the first zero knowledge SNARG of knowledge (zkSNARK) that is secure in the quantum random oracle model.Our main tool is a new lifting lemma that shows how, for a rich class of oracle games, we can generically deduce security against quantum attackers by bounding a natural classical property of these games. This means that in order to prove our theorem we only need to establish classical properties about the Micali construction. This approach not only lets us prove post-quantum security but also enables us to prove explicit bounds that are tight up to small factors.We additionally use our techniques to prove that SNARGs based on interactive oracle proofs (IOPs) with round-by-round soundness are unconditionally secure in the quantum random oracle model. This result establishes the post-quantum security of many SNARGs of practical interest.

2019

TCC

Linear-Size Constant-Query IOPs for Delegating Computation
Abstract

We study the problem of delegating computations via interactive proofs that can be probabilistically checked. Known as interactive oracle proofs (IOPs), these proofs extend probabilistically checkable proofs (PCPs) to multi-round protocols, and have received much attention due to their application to constructing cryptographic proofs (such as succinct non-interactive arguments). The relevant complexity measures for IOPs in this context are prover and verifier time, and query complexity.We construct highly efficient IOPs for a rich class of nondeterministic algebraic computations, which includes succinct versions of arithmetic circuit satisfiability and rank-one constraint system (R1CS) satisfiability. For a time-T computation, we obtain prover arithmetic complexity $$O(T \log T)$$ and verifier complexity polylog(T). These IOPs are the first to simultaneously achieve the state of the art in prover complexity, due to [14], and in verifier complexity, due to [7]. We also improve upon the query complexity of both schemes.The efficiency of our prover is a result of our highly optimized proof length; in particular, ours is the first construction that simultaneously achieves linear-size proofs and polylogarithmic-time verification, regardless of query complexity.

#### Program Committees

- Crypto 2019
- Eurocrypt 2018
- TCC 2017

#### Coauthors

- Eli Ben-Sasson (8)
- Iddo Bentov (1)
- Nir Bitansky (3)
- Jonathan Bootle (2)
- Benedikt Bünz (2)
- Ran Canetti (1)
- Michael A. Forbes (1)
- Ariel Gabizon (3)
- Daniel Genkin (2)
- Lior Goldberg (1)
- Shafi Goldwasser (1)
- Matthew Green (1)
- Jens Groth (1)
- Tom Gur (1)
- Matan Hamilis (1)
- Yuncong Hu (1)
- Yuval Ishai (1)
- Wei-Kai Lin (1)
- Huijia Lin (1)
- Jingcheng Liu (1)
- Mary Maller (1)
- Peter Manohar (1)
- Peihan Miao (1)
- Ian Miers (1)
- Pratyush Mishra (4)
- Dev Ojha (1)
- Rafail Ostrovsky (1)
- Omer Paneth (1)
- Evgenya Pergament (1)
- Michael Riabzev (4)
- Aviad Rubinstein (1)
- Mark Silberstein (1)
- Katerina Sotiraki (1)
- Nicholas Spooner (8)
- Eran Tromer (5)
- Noah Vesely (1)
- Madars Virza (6)
- Nicholas P. Ward (2)
- Eylon Yogev (3)