Smart contract source: en.wikipedia.org/wiki/Smart_contract
This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these template messages)(Learn how and when to remove this template message)
A smart contract is a computer program or a transaction protocol which is intended to automatically execute, control or document legally relevant events and actions according to the terms of a contract or an agreement. The objectives of smart contracts are the reduction of need in trusted intermediators, arbitrations and enforcement costs, fraud losses, as well as the reduction of malicious and accidental exceptions.
Vending machines are mentioned as the oldest piece of technology equivalent to smart contract implementation. 2014's white paper about the cryptocurrency Ethereum describes the Bitcoin protocol as a weak version of the smart contract concept as defined by computer scientist, lawyer and cryptographer Nick Szabo. Since Ethereum, various cryptocurrencies support scripting languages which allow for more advanced smart contracts between untrusted parties.
Smart contracts were first proposed in the early 1990s by Nick Szabo, who coined the term, using it to refer to "a set of promises, specified in digital form, including protocols within which the parties perform on these promises". In 1998, the term was used to describe objects in rights management service layer of the system The Stanford Infobus, which was a part of Stanford Digital Library Project.
Legal status of smart contracts
A smart contract does not necessarily constitute a valid binding agreement at law. Some legal academics claim that smart contracts are not legal agreements, but rather means of performing obligations deriving from other agreements such as technological means for the automation of payment obligations or obligations consisting in the transfer of tokens or cryptocurrencies.
With the 2015's implementation of Ethereum, based on blockchains, "smart contract" is mostly used more specifically in the sense of general purpose computation that takes place on a blockchain or distributed ledger. The US National Institute of Standards and Technology describes a "smart contract" as a "collection of code and data (sometimes referred to as functions and state) that is deployed using cryptographically signed transactions on the blockchain network". In this interpretation, used for example by the Ethereum Foundation or IBM, a smart contract is not necessarily related to the classical concept of a contract, but can be any kind of computer program. A smart contract also can be regarded as a secured stored procedure as its execution and codified effects like the transfer of some value between parties are strictly enforced and can not be manipulated, after a transaction with specific contract details is stored into a blockchain or distributed ledger. That's because the actual execution of contracts is controlled and audited by the platform, not by any arbitrary server-side programs connecting to the platform.
In 2017, by implementing the Decree on Development of Digital Economy, Belarus has become the first-ever country to legalize smart contracts. Belarusian lawyer Denis Aleinikov is considered to be the author of a smart contract legal concept introduced by the decree.
In 2018, a US Senate report said: "While smart contracts might sound new, the concept is rooted in basic contract law. Usually, the judicial system adjudicates contractual disputes and enforces terms, but it is also common to have another arbitration method, especially for international transactions. With smart contracts, a program enforces the contract built into the code." A number of states in the US have passed legislation on the use of smart contracts, such as Arizona, Nevada, Tennessee, and Wyoming.
Smart contracts should therefore be distinguished from smart legal contracts. The latter refers to a traditional natural language legally-binding agreement which has certain terms expressed and implemented in machine readable code.
In the cryptocurrency domain, smart contracts are digitally signed in the same way a cryptocurrency transaction is signed. The signing keys are held in a crypto wallet. Byzantine fault-tolerant algorithms allowed digital security through decentralization to form smart contracts.
Additionally, the programming languages with various degrees of Turing-completeness as a built-in feature of some blockchains make the creation of custom sophisticated logic possible. Measurement using regular expressions showed that only % of smart contracts from Ethereum included recursions and loops — those are connected to halting problem. Due to halting and other security problems, Turing-completeness is considered to be a risk and is deliberately avoided by languages like Vyper.
Notable examples of implementation of smart contracts include the following:
- Bitcoin provides a Turing-incomplete script language that allows the creation of custom smart contracts on top of Bitcoin like multisignature accounts, payment channels, escrows, time locks, atomic cross-chain trading, oracles, or multi-party lottery with no operator.
- Ethereum implements a Turing-complete language on its blockchain, a prominent smart contract framework.
- Ripple (Codius), smart contract development halted in 2015.
- Solidity is an object-oriented smart contract language.
- DAML is a functional smart contract language based on Haskell.
- EOS.IO is a blockchain platform for smart contracts.
- Tezos is a blockchain platform modifying its own set of rules with minimal disruption to the network through an on-chain governance model.
Processes on a blockchain are generally deterministic in order to ensure Byzantine fault-tolerance. Nevertheless, real world application of smart contracts, such as lotteries and casinos, require secure randomness. In fact, blockchain technology reduces the costs for conducting of a lottery and is therefore beneficial for the participants. Randomness on blockchain can be imlemented by using block hashes or timestamps, oracles, commitment schemes, special smart contracts like RANDAO and Quanta as well as sequences from mixed strategy Nash equilibria.
Replicated titles and contract execution
In 1998, Szabo proposed that smart contract infrastructure can be implemented by replicated asset registries and contract execution using cryptographic hash chains and Byzantine fault-tolerant replication. Askemos implemented this approach in 2002 using Scheme (later adding SQLite) as contract script language.
One proposal for using bitcoin for replicated asset registration and contract execution is called "colored coins". Replicated titles for potentially arbitrary forms of property, along with replicated contract execution, are implemented in different projects.
As of 2015[update], UBS was experimenting with "smart bonds" that use the bitcoin blockchain in which payment streams could hypothetically be fully automated, creating a self-paying instrument.
A blockchain-based smart contract is visible to all users of said blockchain. However, this leads to a situation where bugs, including security holes, are visible to all yet may not be quickly fixed. Such an attack, difficult to fix quickly, was successfully executed on The DAO in June 2016, draining US$50 million in Ether while developers attempted to come to a solution that would gain consensus. The DAO program had a time delay in place before the hacker could remove the funds; a hard fork of the Ethereum software was done to claw back the funds from the attacker before the time limit expired.
Issues in Ethereum smart contracts, in particular, include ambiguities and easy-but-insecure constructs in its contract language Solidity, compiler bugs, Ethereum Virtual Machine bugs, attacks on the blockchain network, the immutability of bugs and that there is no central source documenting known vulnerabilities, attacks and problematic constructs.
- Code and Other Laws of Cyberspace
- Decentralized application
- Regulation by algorithms
- Regulation of algorithms
- Ricardian contract (a design pattern to capture the intent of the agreement of parties)
- Secure multiparty computation
- Röscheisen, Martin; Baldonado, Michelle; Chang, Kevin; Gravano, Luis; Ketchpel, Steven; Paepcke, Andreas (1998). "The Stanford InfoBus and its service layers: Augmenting the internet with higher-level information management protocols". Digital Libraries in Computer Science: The MeDoc Approach. Lecture Notes in Computer Science. Springer. 1392: 213–230. doi:10.1007/bfb0052526. ISBN 978-3-540-64493-4.
- Fries, Martin; P. Paal, Boris (2019). Smart Contracts (in German). Mohr Siebeck. ISBN 978-3-16-156911-1. JSTOR j.ctvn96h9r.
- Savelyev, Alexander (14 December 2016). "Contract Law 2.0: "Smart" Contracts As the Beginning of the End of Classic Contract Law". Social Science Research Network. SSRN 2885241. Cite journal requires
- Tapscott, Don; Tapscott, Alex (May 2016). The Blockchain Revolution: How the Technology Behind Bitcoin is Changing Money, Business, and the World. pp. 72, 83, 101, 127. ISBN 978-0670069972.
- Szabo, Nick (1997). "View of Formalizing and Securing Relationships on Public Networks | First Monday". firstmonday.org.
- "White Paper· ethereum/wiki Wiki · GitHub". Archived from the original on 11 January 2014.
- Alharby, Maher; van Moorsel, Aad (26 August 2017). "Blockchain-based Smart Contracts: A Systematic Mapping Study". Computer Science & Information Technology: 125–140. arXiv:1710.06372. doi:10.5121/csit.2017.71011. ISBN 9781921987700. S2CID 725413.
- Morris, David Z. (21 January 2014). "Bitcoin is not just digital currency. It's Napster for finance". Fortune. Retrieved 7 November 2018.
- Schulpen, Ruben R.W.H.G. (1 August 2018). "Smart contracts in the Netherlands - University of Tilburg". uvt.nl. Twente University. Retrieved 26 October 2019.
- Mik, Eliza, Smart Contracts: A Requiem (December 7, 2019). Journal of Contract Law (2019) Volume 36 Part 1 at p 72
- J Cieplak, S Leefatt, ‘Smart Contracts: A Smart Way To Automate Performance’ (2017) 1 Georgia L & Tech Rev 417
- D J Yaga et al, Blockchain Technology Overview, National Institute of Standards and Technology Internal/Interagency Report 8202, 2018, p 54, cited in Mik, Eliza, Smart Contracts: A Requiem (December 7, 2019). Journal of Contract Law (2019) Volume 36 Part 1 at p 71
- Cachin, Christian. "Architecture of the Hyperledger Blockchain Fabric" (PDF). ibm.com.
- Vo, Hoang Tam; Kundu, Ashish; Mohania, Mukesh (2018). "Research Directions in Blockchain Data Management and Analytics" (PDF). Advances in Database Technology - Extending Database Technology (EDBT). OpenProceedings. 21: 446.
Some distributed ledger technologies support an additional capability called a smart contract, which is similar to the concept of stored procedure in classical relational databases to some extent. Smart contracts allow the shared business processes within a business network to be standardised, automated and enforced via computer programs to increase the integrity of the ledger.
- Huckle, Steve; Bhattacharya, Rituparna; White, Martin; Beloff, Natalia (2016). "Internet of Things, Blockchain and Shared Economy Applications". Procedia Computer Science. Elsevier B.V. 98: 463. doi:10.1016/j.procs.2016.09.074.
Firstly, that total quantity of BTC in a transaction's inputs must cover the total number of BTC in the outputs. That rule behaves similarly to a database stored procedure, except that it is impossible to circumvent. Secondly, BTC transactions use public-private key cryptography. That makes BTC act like a database with a publicly auditable per-row permission scheme.
- Makhovsky, Andrei (December 22, 2017). "Belarus adopts crypto-currency law to woo foreign investors". Reuters.
- Chapter 9: Building a Secure Future, One blockchain at a time, US Senate Joint Economic Committee, March 2018.
- "Arizona HB2417 - 2017 - Fifty-third Legislature 1st Regular". LegiScan.
- Hyman Gayle M, Digesti, Matthew P New Nevada legislation recognizes blockchain and smart contract terminologies August 2017, Nevada Lawyer
- Governatori, Guido; Idelberger, Florian; Milosevic, Zoran; Riveret, Regis; Sartor, Giovanni; Xu, Xiwei (2018). "On legal contracts, imperative and declarative smart contracts, and blockchain systems". Artificial Intelligence and Law. 26 (4): 33. doi:10.1007/s10506-018-9223-3. S2CID 3663005.
- Jansen, Marc; Hdhili, Farouk; Gouiaa, Ramy; Qasem, Ziyaad (2020). "Do Smart Contract Languages Need to Be Turing Complete?". Blockchain and Applications. Advances in Intelligent Systems and Computing. Springer International Publishing. 1010: 19–26. doi:10.1007/978-3-030-23813-1_3. ISBN 978-3-030-23812-4.
- Harz, Dominik; Knottenbelt, William (31 October 2018). "Towards Safer Smart Contracts: A Survey of Languages and Verification Methods". arXiv:1809.09805 [cs.CR].
- Тюрин, Алексей Валерьевич; Тюляндин, Иван Владимирович; Мальцев, Владимир; Кириленко, Яков Александрович; Березун, Даниил Андреевич (4 August 2019). "Обзор языков для безопасного программирования смарт-контрактов". Труды Института системного программирования РАН. doi:10.15514/ISPRAS-2019-31(3)-13.
- Atzei, Nicola; Bartoletti, Massimo; Cimoli, Tiziana; Lande, Stefano; Zunino, Roberto (2018), "SoK: unraveling Bitcoin smart contracts" (PDF), 7th International Conference on Principles of Security and Trust (POST), European Joint Conferences on Theory and Practice of Software
- Atzei, Nicola; Bartoletti, Massimo; Cimoli, Tiziana (2017), "A survey of attacks on Ethereum smart contracts" (PDF), 6th International Conference on Principles of Security and Trust (POST), European Joint Conferences on Theory and Practice of Software
- Chatterjee, Krishnendu; Goharshady, Amir Kafshdar; Pourdamghani, Arash (21 February 2019). "Probabilistic Smart Contracts: Secure Randomness on the Blockchain". arXiv:1902.07986 [cs.GT].
- Chen, Tai-yuan; Huang, Wei-ning; Kuo, Po-chun; Chung, Hao (6 August 2020). "Method for Generating Secure Randomness on Blockchain". Retrieved 28 August 2020.
- "DeLottery | Proceedings of the 2019 2nd International Conference on Blockchain Technology and Applications". dl.acm.org. 2019. doi:10.1145/3376044.3376049. S2CID 207880557.
- "randao/randao". randao. 10 July 2020. Retrieved 10 July 2020.
- Nick Szabo (1998). "Secure Property Titles with Owner Authority". Archived from the original on January 15, 2014. Retrieved January 12, 2014.
- Jörg F. Wittenberger (2002). "Askemos a distributed settlement".
- "Proceedings of International Conference on Advances in Infrastructure for e-Business, e-Education, e-Science, and e-Medicine on the Internet" (PDF).
- Martin Möbius (2009). "Erstellung eines Archivierungskonzepts für die Speicherung rückverfolgbarer Datenbestände im Askemos-System". Cite journal requires
- Tom-Steve Watzke (2010). "Entwicklung einer Datenbankschnittstelle als Grundlage für Shop-Systeme unter dem Betriebssystem Askemos". Cite journal requires
- RA Markus Heinker (2007). "Beweiswürdigung elektronischer Dokumente im Zivilprozess unter vergleichender Betrachtung von qualifizierten elektronischen Signaturen nach dem Signaturgesetz und dem Askemos-Verfahren".
- Hal Hodson (20 November 2013). "Bitcoin moves beyond mere money". New Scientist. Retrieved 12 January 2014.
- Ross, Rory (2015-09-12). "Smart Money: Blockchains Are the Future of the Internet". Newsweek. Retrieved 2016-05-27.
- Wigan, David (2015-06-11). "Bitcoin technology will disrupt derivatives, says banker". IFR Asia. Retrieved 2016-05-27.
- Peck, M. (28 May 2016). "Ethereum's $150-Million Blockchain-Powered Fund Opens Just as Researchers Call For a Halt". IEEE Spectrum. Institute of Electrical and Electronics Engineers.
- DuPont, Quinn (2017). "Experiments in Algorithmic Governance: A history and ethnography of "The DAO", a failed Decentralized Autonomous Organization" (PDF). Archived from the original (PDF) on 2017-07-30. Retrieved 29 July 2017.
- Coy, Peter; Kharif, Olga (25 August 2016). "This Is Your Company on Blockchain". Bloomberg Businessweek. Retrieved 2016-12-05.