Part I Introduction

Chainlink (2023) defines staking as “the locking up of cryptocurrency tokens as collateral to help secure a network or smart contract, or to achieve a specific result.” Among all the blockchain applications of the staking mechanism, the Proof-of-Stake (PoS) mechanism is nearly the most famous one. By Sept. 15th, 2022, Ethereum blockchains have switched its consensus mechanism to the PoS system with the Ethereum 2.0 update. The PoS mechanism, in which validators stake ethers (ETH) into a smart contract to participate in transaction verification and block-building process, has supported the Ethereum ecosystem for several months and taken effect in energy-saving and security. In this article, we review the application of the staking mechanisms, especially on the widely used Proof-of-Stake (PoS) consensus mechanism, including the Ethereum blockchain, and alternatives that apply PoS to construct their consensus protocols and secure blockchain systems. Furthermore, we conduct a comparative study to analyze the application of staking mechanisms on Ethereum 2.0, Algorand, and Internet Computer blockchain. In comparison, we extend the understanding of staking mechanism applications from blockchain consensus to on-chain governance. We also provide a taxonomy for comparing staking mechanism designs in participation conditions and incentives, the liquidity of staked assets, and exit conditions. Our exploratory research pays the way for designing future staking mechanisms for various applications and on-chain activities to achieve desired outcomes. 

Part II The Proof-of-Stake Mechanism

2.1 A Sketch of Consensus Mechanisms

Consensus mechanisms are stacks of designs to solve the consensus problems in blockchain systems by facilitating agents to agree on blockchain states and improve reliability between nodes in the network. The designs of consensus mechanisms comprise protocols, incentives, on-chain policies, and other ideas, which have benefited many aspects of blockchain technologies (i.e., incentives designed for the consensus layer (Wang et al. 2019), and protocol designs for network, data, and infrastructure layers (Xiao et al. 2020, Zhang and Lee 2020), etc.) and applications (i.e., cryptocurrencies, decentralized finance (Wang et al. 2019), etc.). We concluded the application of consensus mechanisms on different blockchain layers with some examples in Figure 2.

Soon after implementing Proof-of-Work (PoW) on Bitcoin (Nakamoto 2008), the very first consensus-based cryptocurrency, and the proposed Byzantine Generals Problem (Lamport, Shostak, and Pease 1982), which has become the most famous consensus problem, more consensus mechanisms were invented and applied to support the creation and security of blockchains. Including the mentioned PoW that Bitcoin uses, among the most famous consensus mechanisms are the PoS of Ethereum (Wackerow 2022, Ethereum Developers 2022) and Peercoin (King and Nadal 2012), the Delegated Proof-of-Stake (DPoS) of BitShares (bitshares 2018), the Pure-PoS of Algorand (Algorand, n.d.), and the Practical Byzantine Fault Tolerance (PBFT) of Tendermint (Kwon 2014), which all belong to the Byzantine consensus (Gramoli 2020). We show the mapping between major consensus algorithms and their blockchain use cases in Figure 3. Other consensus algorithms designed by scholars and practitioners include Proof-of-Importance (PoI) (Li, Li, et al. 2017), Proof-of-Activity (PoA) (Bentov et al. 2014), Stellar Consensus Protocol (Mazières n.d.), and CloudPoS (Tosh et al. 2018).

2.2. The Evaluation Features for Consensus Mechanisms.

An emerging literature proposes taxonomies to compare the performance of blockchain consensus algorithms in 4 facets of energy-saving (Zheng et al. 2017, Bach, Mihaljevic, and Zagar 2018), fault tolerance ratio (Mingxiao et al. 2017, Zheng et al. 2017, Bach, Mihaljevic, and Zagar 2018, Chaudhry and Yousaf 2018), scalability (Mingxiao et al. 2017, Chaudhry and Yousaf 2018), and adaptable blockchain type (Chaudhry and Yousaf 2018). Table 1 represents the comparative study of the six major consensus algorithms in the four facets. 

Table 1: The evaluation of famous consensus mechanisms.

As blockchain technology evolves rapidly, the design of consensus algorithms has been facing new challenges and calling for innovative solutions. For example, as blockchains evolve from permissioned to permissionless settings, Pass and Shi (2016, 2017) first proposed a hybrid consensus protocol design model and then rethought and analyzed the difficulties of reaching the consensus in a permissionless blockchain compared with the permissioned settings. After several years, Chan and Shi (2020) looked back to the original permissioned blockchains. They described a paradigm, Streamlet, for constructing consensus protocols on permissioned blockchains, which they proposed to “decipher the past five years of work on consensus partly driven by the cryptocurrency community.”

2.3. Consensus protocols based on the Staking Mechanism.

The Proof-of-Stake consensus mechanism, or PoS, was originally invented to ameliorate the energy waste problem in the PoW mechanism (Saleh 2018). In contrast to the PoW mechanism which determines the block proposer by computing power, the PoS mechanism makes all the miners stake a certain amount of tokens to become validators, uses different lead election mechanisms to select the block proposer, and makes the rest of the validators to validate the proposed block, and incentivizes consensus achievement by designing block rewards. The PoS mechanism has inspired a lot of consensus protocol designs, blockchain attack and security studies, and other feature analyses in crypto-economics (Nguyen et al. 2019).

After the Merge, Ethereum 2.0 has been using a staking mechanism to achieve consensus on its blockchain systems. Among the stack of designs based on the staking mechanism, the consensus protocols, which facilitate the operation of the distributed infrastructure, P2P network, and data storage, play an essential role in blockchains. Therefore, we summarize the representative consensus protocols designed based on the Proof-of-Stake consensus in Table 2. Casper, the consensus protocol run by Ethereum 2.0, combines Casper FFG proof-of-stake (Buterin and Griffith 2019) with the GHOST fork-choice rule (Buterin et al. 2020). 

Table 2: The applications of consensus protocols based on the PoS mechanisms.

2.4. Security Issues on PoS Mechanisms

The security of PoS mechanisms has long been a trending issue of interest. PoS is often considered less secure than PoW because it eliminates how PoW is secured by hashing power, although both face 51% attack. The PoS blockchain faces even more attacks (Gaži, Kiayias, and Russell 2018, Sayeed and Marco-Gisbert 2019). According to the existing literature, scholars have discussed numerous approaches to secure PoS blockchains, including incentive designs, protocol designs, and algorithm designs to prevent potential attacks on blockchains. Table 3 lists some typical works that contributed significantly to PoS security studies.

Table 3. The existing designs to secure PoS blockchains.

Part II A Comparative Study: The Application of the Staking Mechanisms on Ethereum, Algorand, and Internet Computer blockchains.

Most blockchains use the staking mechanism to identify, guide, and incentivize participants for on-chain operations. Ethereum names the participants who meet a specific staking requirement of the entrance as validators. In contrast, participants in Ethereum are validators of Algorand. With the staked assets, validators could participate in different blockchain activities like transaction validation, block-building, and on-chain governance, according to the specific policies. We summarize the application of the staking mechanism in the PoS Ethereum blockchains, Algorand blockchains, and Internet Computer blockchains and comparatively study their technology policy parameters related to the staking mechanisms in Table 3.

3.1. Staking-based Blockchain Activities: Block-building and on-chain governance

Staking mechanisms are to qualify participants for on-chain activities. Although staking-based activities depend on the token economy of different blockchain systems, two major activities that involve the staking mechanism are block-building and on-chain governance. In the block-building process, a validator who has staked a required amount of tokens are able to validate new blocks and verify transactions. Both the Ethereum and Algorand blockchains use the staking mechanism in their block-building process. In contrast, Internet Computer are run by big data centers with credits other than the staking mechanism in the block-building process. 

On-chain governance is a system that enables cryptocurrency blockchains to update themselves via rules encoded in the protocol for proposing, voting, and enacting new policies by participants (Kiayias and Lazos 2022). Both Algorand and Internet Computer blockchains use the staking mechanism in their on-chain governance. Algorand holds quarterly (Jan, April, July, and September) periods for stakeholders to sign in and take part as a governor staking ALGOs in the Algorand Community Governance (“Governance | Algorand Foundation” n.d.)); Similarly, Internet Computer runs an on-chain liquid governance (Ramos 2015) system, the Neural Network System (NNS), that receives real-time governance proposals and votes on proposals based on the staked Internet Computer Protocol (ICP) tokens coined as neurons (“A Detailed Guide to Voting on Proposals and Earning Rewards through the NNS” 2022). 

3.2. The Taxonomy of Staking Mechanism Design

Table 3 also represents a taxonomy of staking mechanism design in participation conditions and incentives, liquidity of staked assets, and exit conditions. To participate in block-building, participants usually have to stake the minimum required amount of tokens and run a blockchain node or use another third-party staking service. And the general incentives to participate include the non-monetary benefit of voting power in blockchain activities. Participants can enjoy the liquidity of staked assets by default or using a liquid staking service. Finally, participants can volunteer to exit from staking mechanisms following specified rules, which may relate to participation incentives or voting power. However, the participation condition and incentives differ across blockchains of various on-chain activities. Below, we compare the specifications of Ethereum, Algorand, and Internet Computer.

Ethereum: According to Johns Gresham’s presentation on Devcon Bogota (Gresham 2022), running an Ethereum node requires a computer with 8-16GB RAM, and 2TB fast SSD storage (currently, all the data on the PoS Ethereum requires 1TB, but the size grows to 10GB per week), and a modern CPU less than five years old (it may require less in the reality as we tested before), and an internet condition with at least 10MB for uploads and downloads, unlimited data, and no slow cellular or WiFi connections. Moreover, One who participates in the PoS Ethereum consensus protocol should stake 32 ETH to become an on-chain validator. In contrast to solo staking, participants can also take part in the staking mechanism without running a full node by choosing staking as a service (SaaS) or staking less than 32 ETH by joining a staking pool. However, both staking as a service (SaaS) and pool-staking have both additional monetary costs and security risks in the delegation of staking to a third party (“Ethereum Staking,” n.d.). In the block-building process, validators vote for the validation of blocks and receive block rewards if they attest correctly. Based on the staking mechanism, Ethereum also uses the slashing mechanism to punish malicious attestations on the blockchain. When malicious attestations happen, the corresponding validators would be slashed accordingly. A heavy slashing may lead directly to insufficient balance in one’s account and push the validator to be exited from its life cycle.

Algorand: For participants who run an Algorand node, according to the developer guideline on Algorand’s official website (Algorand n.d.), there are six node types to choose from to satisfy different on-chain activities, and participants in Algorand consensus protocols should run a non-relay non-archival participation node. The minimum hardware requirements are 4GB of RAM (8GB highly recommended) and a not-too-slow SSD for a computer, and a 100Mbps connection (1Gbps recommended) for the internet. Moreover, the voting power of staked AlGOs is in proportion to the weights of users in a system. Slightly different from other cryptocurrencies that use PoS consensus that expels malicious players, Algorand uses the weights assigned by staking to ensure that an attacker cannot amplify its power and guarantee blockchain security as long as no one holds more than ⅓ of total power. Algorand also uses the staking mechanism in its governance periods. Stakeholders sign in to the governance system and commit ALGOs to become a governor to participate in its community governance. While one committed ALGO represents one vote, the governors must maintain their committed Algo balance throughout each entire 3-month period. When a voting session comes, the governance portal will give all the voting measures, and governors make ZERO-ALGO transactions to vote. Interestingly, Algorand declares it does not participate directly in the voting (Algorand n.d.). Instead, Algorand would give out its favorite choice in the governance portal, and any governor could choose between yes (or choice A), no (or choice B), and vote with the Foundation.

Internet Computer: Unlike the PoS Ethereum and Algorand blockchains, Internet Computer, the only permissioned blockchain among these three, uses the staking mechanism in its on-chain governance to support decentralization and secure its protocol. Correspondingly, people are not required to run a node to take part—one who wishes to take part in the on-chain governance is only required to stake some ICP utility tokens for a required period between six months (the minimum) to eight years (the maximum) to become a governor in the on-chain governance. The staked assets would generate a neuron with a unique neuron ID as the governor’s identifier in the on-chain governance. The incentives are relatively simple—as the on-chain governance comprises three processes of proposing, voting, and enacting, the validators could gain more voting power in proportion to the staking amount and period. But unlike Algorand, Internet Computer takes part in the voting session directly with a large percentage of the voting power.

Table 3: The application of the staking mechanism on PoS Ethereum, Algorand, and Internet Computer: a comparative study.

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