Homomorphic Time-Lock Puzzles and Applications

Malavolta, Giulio; Thyagarajan, Sri Aravinda Krishnan

doi:10.1007/978-3-030-26948-7_22

Cited by 62 publications

(35 citation statements)

References 23 publications

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“…Later, [10,21] proposed a scheme which also let a puzzle generator prove (in Zero-knowledge) to a puzzle solver that the correct solution will be recovered after a certain time. Recently, [38,11] propose homomorphic time-lock puzzles, where an arbitrary function can be run over puzzles before they are solved. In the protocols, all puzzles have an identical time parameter, and their solutions are supposed to be discovered at the same time.…”

Section: Related Workmentioning

confidence: 99%

Multi-instance Publicly Verifiable Time-Lock Puzzle and Its Applications

Abadi

Kiayias

2021

Lecture Notes in Computer Science

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Time-lock puzzles are elegant protocols that enable a party to lock a message such that no one else can unlock it until a certain time elapses. Nevertheless, existing schemes are not suitable for the case where a server is given multiple instances of a puzzle scheme at once and it must unlock them at different points in time. If the schemes are naively used in this setting, then the server has to start solving all puzzles as soon as it receives them, that ultimately imposes significant computation cost and demands a high level of parallelisation. We put forth and formally define a primitive called "multi-instance time-lock puzzle" which allows composing a puzzle's instances. We propose a candidate construction: "chained time-lock puzzle" (C-TLP). It allows the server, given instances' composition, to solve puzzles sequentially, without having to run parallel computations on them. C-TLP makes black-box use of a standard time-lock puzzle scheme and is accompanied by a lightweight publicly verifiable algorithm. It is the first time-lock puzzle that offers a combination of the above features. We use C-TLP to build the first "outsourced proofs of retrievability" that can support real-time detection and fair payment while having lower overhead than the state of the art. As another application of C-TLP, we illustrate in certain cases, one can substitute a "verifiable delay function" with C-TLP, to gain much better efficiency.

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Section: Related Workmentioning

confidence: 99%

Multi-instance Publicly Verifiable Time-Lock Puzzle and Its Applications

Abadi

Kiayias

2021

Lecture Notes in Computer Science

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“…Thus, most applications that would need to enforce some minimal amount of work, with the finegrained capability of configuring the amount of information leakage based on the computation power of the adversary, would need our modified time-capsules notion and construction. Other recent works [17,39] introduced the notion of homomorphic time-lock puzzles, which allows to combine homomorphically time puzzles and then open a single puzzle containing the result of the computation. Homomorphic time-lock puzzles also allow to design decentralized auctions, however the known constructions either require indistinguishability obfuscation [39] or multi-key fully homomorphic encryption [17].…”

Section: Related Workmentioning

confidence: 99%

“…Other recent works [17,39] introduced the notion of homomorphic time-lock puzzles, which allows to combine homomorphically time puzzles and then open a single puzzle containing the result of the computation. Homomorphic time-lock puzzles also allow to design decentralized auctions, however the known constructions either require indistinguishability obfuscation [39] or multi-key fully homomorphic encryption [17]. The auction-based mining proposed in [23], similar to our work, brings the notion of time-lock puzzles to the blockchain by having miners force open unopened puzzles.…”

Section: Related Workmentioning

confidence: 99%

Gage MPC: Bypassing Residual Function Leakage for Non-Interactive MPC

Almashaqbeh¹,

Benhamouda²,

Han

et al. 2021

Proceedings on Privacy Enhancing Technologies

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Existing models for non-interactive MPC cannot provide full privacy for inputs, because they inherently leak the residual function (i.e., the output of the function on the honest parties’ input together with all possible values of the adversarial inputs). For example, in any non-interactive sealed-bid auction, the last bidder can figure out what was the highest previous bid. We present a new MPC model which avoids this privacy leak. To achieve this, we utilize a blockchain in a novel way, incorporating smart contracts and arbitrary parties that can be incentivized to perform computation (“bounty hunters,” akin to miners). Security is maintained under a monetary assumption about the parties: an honest party can temporarily supply a recoverable collateral of value higher than the computational cost an adversary can expend. We thus construct non-interactive MPC protocols with strong security guarantees (full security, no residual leakage) in the short term. Over time, as the adversary can invest more and more computational resources, the security guarantee decays. Thus, our model, which we call Gage MPC, is suitable for secure computation with limited-time secrecy, such as auctions. A key ingredient in our protocols is a primitive we call “Gage Time Capsules” (GaTC): a time capsule that allows a party to commit to a value that others are able to reveal but only at a designated computational cost. A GaTC allows a party to commit to a value together with a monetary collateral. If the original party properly opens the GaTC, it can recover the collateral. Otherwise, the collateral is used to incentivize bounty hunters to open the GaTC. This primitive is used to ensure completion of Gage MPC protocols on the desired inputs. As a requisite tool (of independent interest), we present a generalization of garbled circuit that are more robust: they can tolerate exposure of extra input labels. This is in contrast to Yao’s garbled circuits, whose secrecy breaks down if even a single extra label is exposed. Finally, we present a proof-of-concept implementation of a special case of our construction, yielding an auction functionality over an Ethereum-like blockchain.

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“…The second is [23] in which the authors proposed homomorphic time-lock puzzles. To reduce computational overhead or decoding in time-lock puzzles, [23] proposes the method that combines all the puzzles into one puzzle through a homomorphic function and then decodes that puzzle. This method has the advantage of not having to solve all the puzzles.…”

Section: Time-release Cryptographymentioning

confidence: 99%

Practical Time-Release Blockchain

2020

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Time-release cryptography is a special encryption technique that allows a message to be hidden for some time. The previous schemes have shortcomings in that the encryptor should predict the decryptor’s computing power precisely or the trusted agent should be always available. In this paper, we propose a new, practical time-release blockchain, and find the key to decrypt the content after a certain time. In order to verify the effectiveness of the blockchain system automatically, which uses the proof-of-work (PoW) and the consensus algorithm in the the proposed technique, we have implemented a prototype version of our blockchain system using Python. The proposed method has the following advantages. First, the decryption time is automatically adjusted, even if the miner’s computing power changes over time. Second, unlike previous time-lock puzzle schemes, our algorithm does not require additional computation work for solving the puzzle. Third, our scheme does not need any trusted agents (third parties). Fourth, the proposed method uses standard cryptographic algorithms.

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Homomorphic Time-Lock Puzzles and Applications

Cited by 62 publications

References 23 publications

Multi-instance Publicly Verifiable Time-Lock Puzzle and Its Applications

Multi-instance Publicly Verifiable Time-Lock Puzzle and Its Applications

Gage MPC: Bypassing Residual Function Leakage for Non-Interactive MPC

Practical Time-Release Blockchain

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