User:Monica Poucheva-Murray/sandbox

Ouroboros (blockchain protocol)
Ouroboros is a permissionless, proof-of-stake blockchain consensus protocol that can run both permissionless and permissioned blockchains. Unlike most other blockchain innovations at the time, such as Bitcoin and Ethereum, which were announced in commercial white papers by developers, Ouroboros was first described in an academic paper that underwent peer review. The paper was published at the Annual International Cryptology Conference in 2017. According to Google Scholar, it is the most widely-cited paper on proof of stake theory.

Kiayias et al describe Ouroboros as “the first blockchain protocol based on proof of stake with rigorous security guarantees” and as having “security properties … comparable to those achieved by the bitcoin blockchain protocol”. These claims are supported by formal mathematical proofs.

Later in 2017, it was implemented by IOHK as the basis of the Cardano blockchain and the Ada cryptocurrency, which is one of the world’s leading cryptocurrencies by “market capitalization”.

A paper released on ePrint by Elaine Shi and colleagues at Cornell University had claimed to provide “the first formal, end-to-end proof of a proof-of-stake system’, called Snow White, but as the authors later stated: “A closely related work (independent and concurrent from our effort) known as Ouroboros was released about 10 days before Snow White.” The Ouroboros paper discusses using a “similar reward mechanism” to Fruitchains, a “fair” proof-of-work blockchain, proposed by Rafael Pass and Shi at Cornell.

Academic team
The authors of the original Ouroboros paper were Professor Aggelos Kiayias (University of Edinburgh), Professor Alexander Russell (University of Connecticut), Dr. Bernardo David (IT University of Copenhagen), and Professor Roman Oliynykov (National University of Kharkiv), one of the authors of the Kalyna cypher

Professor Kiayias is head of the Blockchain Technology Laboratory at the University of Edinburgh, which is linked to laboratories at the Tokyo Institute of Technology, and the National and Kapodistrian University of Athens. Some of the work received funding as part of the PRIViLEDGE project to develop distributed ledger technologies under the European Union's Horizon 2020 research and innovation programme.

Development stages
Ouroboros has expanded into a set of protocols to support the development of Cardano and other blockchains, with features such as hard forks, decentralisation and stake pools, smart contracts, and voting by network participants. In 2020, the original version (retrospectively referred to as Ouroboros Classic) was replaced running the Cardano blockchain with Ouroboros Praos. The later papers have yet to be peer-review published.

1.	Ouroboros-BFT (Byzantine fault tolerant) (2018) : a simple BFT-style consensus protocol (rather than the usual Nakamoto-style consensus) that enabled a Cardano code change in 2020 from Classic to Praos versions of Ouroboros using a “hard fork combinator”.

2.	Ouroboros Praos (2018) ]: able to support more users and the staking process while being secure against Distributed Denial of Service (DDoS) and other “adaptive” attacks.

3.	Ouroboros Genesis (2018) : avoids the need for a recent checkpoint and proves the protocol is secure under dynamic availability for trustless joining and participating.

4.	Reward sharing and stake pools (2018) : applies game theory to reward-sharing schemes in projects with many stakeholders such as the maintenance of a proof-of-stake blockchain. This team on this work included Gödel Prize winner Elias Koutsoupias.

5.	Ouroboros Chronos (2019) : removes the need to use a common clock such as the internet’s Network Time Protocol.

6.	Ouroboros Crypsinous (2019) : “the first formally analysed privacy-preserving proof-of-stake blockchain protocol”. Uses a coin evolution technique relying on SNARKs and key-private forward secure encryption.

7.	Clepsydra: (2019) : a version of Ouroboros that uses the notion of relative time to remove the assumption of synchronization in the original protocol. It was described by Handan Kılınç Alper a researcher at the Web3 Foundation.

8.	Account management and maximizing participation in stake pools (2020).

9.	Optimizing transaction throughput with proof-of-stake protocols (2020). This research brought in Alexander Russell of the University of Connecticut.

10.	Fast settlement using ledger combiners (2020). A security-amplifying combiner composes blockchains in parallel to speed up response.

11.	Kachina (2020) : a security model for private smart contracts.

12.	Hydra (2020) : an off-chain scalability architecture for high transaction throughput with low latency, and minimal storage per node.

Applications of Ouroboros
The academic publishing, and open-source implementation by IOHK, has led to Ouroboros being adopted by, or influencing, many other blockchain developments. A 2019 academic paper reviewing PoS protocols that had been implemented in practice said Ouroboros has been adopted by Sp8de, a blockchain-based platform for gaming. However, this had yet to materialise.

Coda is developing “a cryptocurrency with a tiny portable blockchain” for web-based cryptocurrency apps. The company uses Ouroboros Praos to fix the blockchain size at 22KB, compared with “22TB and increasing” for other blockchains. Concordium, a company that aims to help businesses use blockchain technology, has a proof-of-stake mechanism that is a “simplified variation of Ouroboros Praos”. Bernardo David, one of the authors of the original Ouroboros paper “collaborates closely with Concordium on consensus protocols and multiparty computation”. The Zen Blockchain Foundation based its sidechain consensus protocol for Horizen on a modified version of Ouroboros. A prototype of the OmniLedger blockchain was built on Ouroboros and Algorand protocols. Researchers at Stuttgart University proved that Hyperledger Fabric achieves accountability using a model “similar in spirit and inspired by ... the recent work on the Ouroboros family”.

Analysis and criticism of Ouroboros
Ouroboros has been compared to other PoS protocols in several papers:

•	Nguyen et al review Ouroboros, Chains-of-Activity, Casper, Algorand and Tendermint, and assess the ways rewards and network stake impact decentralization. •	Wand et al provide a survey of consensus mechanisms. •	Ferdous et al, describe “three notable BFT PoS algorithms that have had significant uptake in practice: Tendermint, CTFG (Casper) and Ouroboros.” •	Buterin et al briefly describe eight PoS protocols.

In 2018, a comparison by Professor Kiayias of Ouroboros and Casper, the proof-of-stake protocol announced by Ethereum to replace proof of work, led to a strongly worded response by Vitalik Buterin, one of the Ethereum founders. The Reddit post began: “They're very clearly writing a hit piece, and not genuinely engaging with any of the actual tradeoffs in consensus design or trying to understand Casper.”