Hedera
  • Welcome to Hedera — let’s build the future
  • Getting Started
    • Environment Setup
    • Web2 Developers
      • Transfer HBAR
      • Create a Token
      • Create a Topic
    • EVM Developers
      • Deploy a Contract
  • Tutorials
    • Smart Contracts
      • How to Mint & Burn an ERC-721 Token Using Hardhat and Ethers (Part 1)
      • How to Set Access Control, a Token URI, Pause, and Transfer an ERC-721 Token Using Hardhat (Part 2)
      • How to Upgrade an ERC-721 Token with OpenZeppelin UUPS Proxies and Hardhat (Part 3)
      • How to Verify a Smart Contract on HashScan
      • Deploy a Smart Contract Using Remix
      • Deploy a Smart Contract Using Hardhat and Hiero JSON-RPC Relay
      • Deploy Your First Smart Contract
      • Deploy a Contract Using the Hedera Token Service
      • Send and Receive HBAR Using Solidity Smart Contracts
      • Deploy By Leveraging Ethereum Developer Tools On Hedera
      • Deploy a Subgraph Using The Graph and Hedera JSON-RPC Relay
      • Deploy Smart Contracts on Hedera Using Truffle
      • The Power of Native Hedera Tokens as ERC-20 Tokens: A step-by-step guide
      • HTS x EVM - Part 1: How to Mint NFTs
      • HTS x EVM - Part 2: KYC & Update
      • HTS x EVM - Part 3: How to Pause, Freeze, Wipe, and Delete NFTs
      • Hedera Smart Contracts Workshop
        • Setup
        • Solidity
        • Hedera SDK JS
        • Hardhat and EthersJs
        • Outro
      • Foundry
        • How to Setup Foundry and Write a Basic Unit Test
        • How to Deploy and Verify a Hedera Smart Contract with Foundry
        • How to Test A Solidity Event
        • How to Fork Testnet on Latest Block
    • Consensus
      • Submit Your First Message
      • Submit Message to Private Topic
      • Query Messages with Mirror Node
    • Tokens
      • Create and Transfer Your First NFT
      • Create and Transfer Your First Fungible Token
      • Create and Transfer an NFT using a Solidity Contract
      • Structure Your Token Metadata Using JSON Schema V2
      • Hedera Token Service - Part 1: How to Mint NFTs
      • Hedera Token Service - Part 2: KYC, Update, and Scheduled Transactions
      • Hedera Token Service - Part 3: How to Pause, Freeze, Wipe, and Delete NFTs
      • Create Your First Frictionless Airdrop Campaign
    • Local Node
      • How to Run Hedera Local Node in a Cloud Development Environment (CDE)
        • Run a Local Node in Gitpod
        • Run a Local Node in Codespaces
      • How to Set Up a Hedera Local Node
      • Set Up a Hedera Local Node using the NPM CLI
    • More Tutorials
      • Create and Fund Your Hedera Testnet Account
      • How to Create a Personal Access Token (API Key) on the Hedera Portal
      • How to Auto-Create Hedera Accounts with HBAR and Token Transfers
      • How to Configure a Mirror Node and Query Data
      • How to Generate a Random Number on Hedera
      • Get Started with the Hedera Consensus Service Fabric Plugin
        • Virtual Environment Setup
      • Schedule Your First Transaction
      • How to Connect to Hedera Networks Over RPC
        • Configuring Hashio RPC endpoints
        • Configuring Hiero JSON-RPC Relay endpoints
        • Configuring Validation Cloud RPC endpoints
      • JavaScript Testing
      • Create a Hedera DApp Integrated with WalletConnect
      • How to Connect MetaMask to Hedera
    • Demo Applications
    • Starter Projects
    • Building on Hedera (course)
  • Networks
    • Mainnet
      • Mainnet Accounts
      • Mainnet Consensus Nodes
        • Node Requirements
          • FAQ
      • Fees
        • Transaction Records
    • Testnets
      • Testnet Accounts
      • Testnet Consensus Nodes
    • Localnet
      • Single Node Configuration
      • Multinode Configuration
    • Network Explorers and Tools
    • Release Notes
      • Consensus Node
      • Hedera Mirror Node
  • Core Concepts
    • Accounts
      • Account Creation
      • Auto Account Creation
      • Account Properties
    • Keys and Signatures
    • Schedule Transaction
    • Smart Contracts
      • Understanding Hedera's EVM Differences and Compatibility
        • For EVM Developers Migrating to Hedera
          • Accounts, Signature Verification & Keys (ECDSA vs. ED25519)
          • JSON-RPC Relay and EVM Tooling
          • Token Management with Hedera Token Service
          • Decimal Handling (8 vs. 18 Decimals)
          • Handling HBAR Transfers in Contracts
        • For Hedera-Native Developers Adding Smart Contract Functionality
          • Integrating ED25519 Accounts and Advanced Features Into Smart Contracts
          • JSON-RPC Relay and State Queries
          • Extending Token Management with Smart Contracts
      • Creating Smart Contracts
      • Compiling Smart Contracts
      • System Smart Contracts
        • Hedera Account Service
        • Hedera Schedule Service
      • Gas and Fees
      • JSON-RPC Relay
      • Deploying Smart Contracts
      • Smart Contract Addresses
      • Verifying Smart Contracts
      • Smart Contract Traceability
      • Tokens Managed by Smart Contracts
        • ERC-20 (Fungible Tokens)
        • ERC-721 (Non-Fungible Token)
        • ERC-3643 Real World Assets (RWA)
        • ERC-1363 (Payable Tokens)
        • Hedera Token Service System Contract
      • Wrapped HBAR (WHBAR)
      • Smart Contract Rent
      • Smart Contract Security
      • EVM Archive Node Queries
    • Tokens
      • Tokenization on Hedera
      • Hedera Token Service (HTS) Native Tokenization
        • Token Types and ID Formats
        • Token Properties
        • Token Creation
        • Custom Fee Schedule
        • Token Airdrops
      • ERC/EVM-Compatible Tokenization
      • Hybrid (HTS + EVM ) Tokenization
    • Staking
      • Staking Program
      • Stake HBAR
    • Hashgraph Consensus Algorithm
      • Gossip About Gossip
      • Virtual Voting
    • Transactions and Queries
      • Transaction Properties
    • State and History
    • Mirror Nodes
      • Hedera Mirror Node
      • One Click Mirror Node Deployment
      • Run Your Own Mirror Node
        • Run Your Own Mirror Node with Google Cloud Storage (GCS)
        • Run Your Mirror Node with Amazon Web Services S3 (AWS)
  • Open Source Solutions and Integrations
    • AI Studio on Hedera
      • ElizaOS Plugin for Hedera
      • Hedera AI Agent Kit
      • MCP Server
      • OpenConvAI
    • AI Tools for Developers
      • Hedera Hivemind
      • Kapa AI
    • Asset Tokenization Studio (ATS)
      • Web User Interface (UI)
      • Frequently Asked Questions (FAQs)
    • HashioDAO
      • Governance Token DAO
      • NFT DAO
      • Multisig DAO
      • DAO Proposals
      • Local Environment Setup
    • Hedera CLI
    • Hedera Contract Builder
    • Hedera Custodians Library
      • How to use it
    • Hedera Developers Code Repository
    • Hedera Developer Playground
    • Hedera Wallet Snap By MetaMask
      • Hedera Wallet Snap Documentation
      • Tutorial: MetaMask Snaps – What Are They and How to Use Them
    • Interoperability and Bridging
      • LayerZero
    • NFT Studio
      • Airdrop List Verifier
      • Metadata Validator
      • NFT Rarity Inspector
      • NFT Token Holders List Builder
      • NFT Risk Calculator
      • Token Balance Snapshot
      • Hedera NFT SDK
    • Oracle Networks
      • Chainlink Oracles
      • Pyth Oracles
      • Supra Oracles
    • Stablecoin Studio
      • Core Concepts
      • Web UI Application
      • CLI Management
      • TypeScript SDK
    • Hedera Guardian
    • Hedera WalletConnect
  • SDKs & APIs
    • SDKs
      • Build Your Hedera Client
      • Set Up Your Local Network
      • Network Address Book
      • Keys
        • Generate a new key pair
        • Import an existing key
        • Create a key list
        • Create a threshold key
        • Generate a mnemonic phrase
        • Recover keys from a mnemonic phrase
      • HBAR
      • Specialized Types
      • Pseudorandom Number Generator
      • Transactions
        • Create a Batch Transaction
        • Transaction ID
        • Modify transaction fields
        • Create an unsigned transaction
        • Manually sign a transaction
        • Submit a transaction
        • Sign a multisignature transaction
        • Get a transaction receipt
        • Get a transaction record
      • Schedule Transaction
        • Schedule ID
        • Create a schedule transaction
        • Sign a scheduled transaction
        • Delete a schedule transaction
        • Get schedule info
        • Network Response Messages
      • Queries
      • General Network Response Messages
      • Accounts and HBAR
        • Create an account
        • Update an account
        • Transfer cryptocurrency
        • Approve an allowance
        • Delete an allowance
        • Delete an account
        • Get account balance
        • Get account info
        • Network Response Messages
      • Consensus Service
        • Create a topic
        • Update a topic
        • Submit a message
        • Delete a topic
        • Get topic messages
        • Get topic info
        • Network Response
      • Token Service
        • Token ID
        • NFT ID
        • Token types
        • Create a token
        • Custom token fees
        • Update a token
        • Update token custom fees
        • Update NFT metadata
        • Transfer tokens
        • Airdrop a token
        • Claim a token
        • Cancel a token
        • Reject a token
        • Delete a token
        • Mint a token
        • Burn a token
        • Freeze an account
        • Unfreeze an account
        • Enable KYC account flag
        • Disable KYC account flag
        • Associate tokens to an account
        • Dissociate tokens from an account
        • Pause a token
        • Unpause a token
        • Wipe a token
        • Atomic swaps
        • Get account token balance
        • Get token info
        • Get NFT info
        • Network Response Messages
      • File Service
        • Create a file
        • Append to a file
        • Update a file
        • Delete a file
        • Get file contents
        • Get file info
        • Network Response Messages
      • Smart Contract Service
        • Delegate Contract ID
        • Create a smart contract
        • Update a smart contract
        • Delete a smart contract
        • Call a smart contract function
        • Ethereum transaction
        • Get a smart contract function
        • Get smart contract bytecode
        • Get smart contract info
        • Hedera Service Solidity Libraries
        • Network Response Messages
      • Signature Provider
        • Provider
        • Signer
        • Wallet
        • Local Provider
    • Mirror Node REST API
      • Accounts
      • Balances
      • Blocks
      • Schedule Transactions
      • Smart Contracts
      • Tokens
      • Topics
      • Transactions
      • Network
    • Hedera Consensus Service gRPC API
    • Hedera APIs
      • Basic Types
        • AccountAmount
        • AccountID
        • ContractID
        • CryptoAllowance
        • CurrentAndNextFeeSchedule
        • FeeComponents
        • FeeData
        • FeeSchedule
        • FileID
        • Fraction
        • HederaFunctionality
        • Key
        • KeyList
        • NftAllowance
        • NftTransfer
        • NodeAddress
        • NodeAddressBook
        • RealmID
        • ScheduleID
        • SemanticVersion
        • ServicesConfigurationList
        • ServiceEndpoint
        • Setting
        • ShardID
        • Signature
        • SignatureList
        • SignatureMap
        • SignaturePair
        • SubType
        • TransferList
        • TransactionID
        • ThresholdKey
        • ThresholdSignature
        • TokenAllowance
        • TokenBalance
        • TokenBalances
        • TokenFreezeStatus
        • TokenPauseStatus
        • TokenID
        • TokenKycStatus
        • TokenRelationship
        • TokenTransferList
        • TokenType
        • TokenSupplyType
        • TopicID
        • TransactionFeeSchedule
      • Cryptocurrency Accounts
        • CryptoService
        • CryptApproveAllowance
        • CryptoDeleteAllowance
        • CryptoCreate
        • CryptoTransfer
        • CryptoUpdate
        • CryptoDelete
        • CryptoGetAccountBalance
        • CryptoGetAccountRecords
        • CryptoGetInfo
        • CryptoGetStakers
      • Consensus Service
        • Consensus Service
        • ConsensusCreateTopic
        • ConsensusUpdateTopic
        • ConsensusSubmitMessage
        • ConsensusDeleteTopic
        • ConsensusTopicInfo
        • ConsensusGetTopicInfo
      • Schedule Service
        • ScheduleService
        • SchedulableTransactionBody
        • ScheduleCreate
        • ScheduleDelete
        • ScheduleSign
        • ScheduleGetInfo
      • Token Service
        • TokenService
        • CustomFees
          • AssessedCustomFee
          • CustomFee
          • FractionalFee
          • FixedFee
          • RoyaltyFee
        • TokenCreate
        • TokenUpdate
        • TokenFeeScheduleUpdate
        • TokenDelete
        • TokenMint
        • TokenBurn
        • TokenFreezeAccount
        • TokenUnfreezeAccount
        • TokenGrantKyc
        • TokenRevokeKyc
        • TokenAssociate
        • TokenDissociate
        • TokenWipeAccount
        • TokenPause
        • TokenUnpause
        • TokenGetInfo
        • TokenGetNftInfo
        • TokenGetNftInfos
        • TokenGetAccountNftInfo
      • File Service
        • FileService
        • FileCreate
        • FileAppend
        • FileUpdate
        • FileDelete
        • FileGetContents
        • FileGetInfo
      • Smart Contracts
        • SmartContractService
        • ContractCall
        • ContractCallLocal
        • ContractCreate
        • ContractUpdate
        • ContractDelete
        • ContractGetByteCode
        • ContractGetInfo
        • ContractGetRecords
      • Miscellaneous
        • Duration
        • ExchangeRate
        • Freeze
        • FreezeType
        • GetByKey
        • GetBySolidityID
        • NetworkGetVersionInfo
        • NetworkService
        • Query
        • QueryHeader
        • Response
        • ResponseCode
        • ResponseHeader
        • SystemDelete
        • SystemUndelete
        • TimeStamp
        • Transaction
        • TransactionBody
        • TransactionContents
        • TransactionGetFastRecord
        • TransactionGetReceipt
        • TransactionGetRecord
        • TransactionReceipt
        • TransactionRecord
        • TransactionResponse
        • UncheckedSubmit
    • Hedera Status API
  • Support & Community
    • Glossary
    • Contributing to Hedera documentation
      • Contribution Guidelines
        • Creating Issues
        • Creating Pull Requests
        • Hedera Improvement Proposal (HIP)
        • Submit Demo Applications
      • Style Guide
        • Understanding different types of documentation
        • Use of HBAR and tinybars
        • Use of web2 and web3
        • Language and grammar
        • Formatting
        • Punctuation
        • GitBook Markdown Syntax
    • Discord
    • GitHub
    • Stack Overflow
    • Hedera Blog
    • Bug Bounty
    • Hedera Help
    • Documentation Survey
    • Meetups
    • Brand Guidelines
    • Status Page
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INTRODUCTION

  • Fees
  • Core Concepts
  • Network Information

TOOLS

  • Bridge
  • Oracles
  • Explorers
  • Developer Portal & Faucet

RESOURCES

  • Status
  • Bug Bounty
  • Build on Hedera (course)
  • Documentation Survey
On this page
  • Divide Rounds
  • Decide Fame
  • Find Order

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  1. Core Concepts
  2. Hashgraph Consensus Algorithm

Virtual Voting

It is not enough to ensure that every member knows every event. It is also necessary to agree on a linear ordering of the events, and thus of the transactions recorded inside the events. Most Byzantine fault tolerance protocols without a leader depend on members sending each other votes...Some of these protocols require receipts on votes sent to everyone...And they may require multiple rounds of voting, which further increases the number of voting messages sent.

This pure voting approach becomes bandwidth prohibitive and impractical in a network of any significant size but has the properties of being the fairest and most secure method of reaching consensus. The hashgraph algorithm implements voting that achieves the same fair and secure properties but is also very fast and practical. It accomplishes this through virtual voting.

The hashgraph algorithm does not require any votes to be sent across the network to calculate the votes of each member. Members can calculate every other member’s votes by internally looking at each of their copies of the hashgraph and applying the virtual voting algorithm. Votes are calculated locally as a function of the ancestors of a given event.

This virtual voting has several benefits. In addition to saving bandwidth, it ensures that members always calculate their votes according to the rules. If Alice is honest, she will calculate virtual votes for the virtual Bob that are honest. Even if the real Bob is a cheater, he cannot attack Alice by making the virtual Bob vote incorrectly.

With this virtual voting algorithm, Byzantine agreement is guaranteed.

Virtual voting happens in 3 steps:

  1. Divide Rounds

  2. Decide Fame

  3. Find Order

Divide Rounds

To begin the process of virtual voting, we must first define rounds and witnesses. In the hashgraph history, the first event for a member’s node is that node’s first witness. The first witness is the beginning of the first round (r) for that node. All subsequent events are part of that first round until a new witness is discovered. A witness is discovered when a node creates a new event that can strongly see ⅔ of the witnesses in the current round. For example, event w can strongly see event x when w can trace its ancestry through parent relationships that pass through other events that reside on at least ⅔ of the member nodes. When an event is determined to strongly see ⅔ of the witness of the current round, that event is considered the next witness for that node. That new witness is the first event in the next round (r+1) for that node. Each event is assigned a round as the event is added to the hashgraph.

procedure divideRounds

for each event x
    r <- max round of parents of x (or 1 if none exist)
    if x can strongly see more than 2n/3 round r witnesses
        x.round <- r+1
    else
      x.round <- r
    x.witness <- (x has no self parent)
                or (x.round > x.selfParent.round)

Decide Fame

The next step is deciding whether a witness is a famous witness or not. A witness is famous if many of the witnesses in the next round can see it, and it is not famous if many can’t. Event A can see Event B if Event B is an ancestor of Event A. When deciding the fame of Witness A, we must look at the witnesses of the following round. If the witnesses of the following round can see Witness A, they count as a vote in favor of Witness A’s fame. Likewise, if a witness in the next round can not see Witness A, then that witness’ vote is that Witness A is not famous. In order for Witness A to be considered famous, a future witness must be able to strongly see that at least ⅔ of voting witnesses have voted in favor of Witness A being famous. If ⅔ of voting witnesses have voted that Witness A is not famous, then Witness A will be decided to be not famous.

Find Order

Now that we have calculated the all witnesses of a round to be famous or not famous, we can determine the order of events that occurred before the famous witness events. This is done by calculating:

  1. The round received for all events that have yet to be ordered and that have occurred before a round where the fame of all witnesses has been decided. The event’s round received is the first round where all famous witnesses of that round can see (or are descendants of) the event in question.

  2. The timestamp for each event. This is done by gathering the earliest ancestors of the famous witnesses of the round received that are also descendants of the event in question, and taking the median timestamp of those gathered events.

  3. The ordering of events first by: round received, consensus timestamp, then signature.

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