Wrapped Bitcoin (WBTC) - the first ERC20 token backed 1:1 with Bitcoin. Completely transparent. 100% verifiable. Community led.

  • With the rise in popularity of ERC20, digital tokens in the Ethereum ecosystem have emerged
    as an important asset class. These tokens have all the advantages that blockchains and
    Ethereum have to offer in terms of transparency in total number of coins, owners, minting, fast
    confirmation times, transactions details and smart contract execution. Tokens on the Ethereum
    blockchain can serve several different functions; this paper will specifically focus on asset
    backed or wrapped tokens. The prices of these tokens reflect the price of the asset backing
    them and hence they can also be called "stable coins". Asset backed tokens are usually done
    in two different ways:
    ● Algorithmic - This is a mechanism followed by some tokens on Ethereum where
    demand and supply are controlled by smart contracts in order to keep the price of the
    token in line with a fiat currency. Some examples of this are Dai, Basis, Carbon, and
    ● Centralized - Assets are stored with an organization which publishes proof of reserves.
    This is the case with Tether, True USD, USDC (USD), Digix (gold), Globcoin (a mix of fiat
    currencies), and AAA reserve (governmental bonds)
    Wrapped tokens follow the centralized model, but instead of relying entirely on one institution,
    they rely on a consortium of institutions performing different roles in the network. This
    whitepaper proposes a framework for issuing asset backed tokens by addressing challenges
    with scalability, trust, regulation, and governance. The first wrapped token we launch will be an
    ERC20 token backed by Bitcoin (BTC) and will be appropriately named, "Wrapped BTC"
    (WBTC). Unlike centralized solutions (USD), WBTC will be fully accounted for and proof of
    reserves posted on the BTC chain.
    There is no additional secondary utility/payment token required to use WBTC, and no transfer
    fees other than blockchain fees. WBTC uses a simple federated governance model and strives
    to promote usability.

    Use Cases


    The act of tokenizing assets can:
    ● Increase speed of transactions
    Ethereum blocks are created every ~15 seconds and it is possible to have a fair deal of
    confidence in the irrevocability of a transaction in less than 5 minutes. This speed is
    faster than transacting natively compared to many other assets including Bitcoin, gold,
    and fiat currencies
    ● Reduce the number of intermediaries
    One of the key benefits of assets on a blockchain is their ability to be transacted
    without intermediaries. This can be done through atomic swaps, decentralized
    exchange protocols, and lightning/raiden style channels.
    ● Enhance security
    Tokenization enables users to have full control of private keys of the asset. Users who
    do not want to hold keys can reduce counterparty risk by moving it from exchanges to
    a security-focused custodian.
    ● Usability
    The ERC20 standard has been adopted by a large number of institutions and products.
    This provides users with a variety of exchanges, wallets, and Dapps to use while
    handling their tokenized asset. They also have the ability to move tokens quickly, 24/7.
    ● Improve Transparency
    The total number of tokens, token creation transactions, token removal transactions,
    number of token holders, and rules for transfers can be seen on a public block explorer
    by anyone. This level of transparency is not usually available for assets like fiat
    currencies, commodities, and stock.
    Liquidity on decentralized exchanges and dapps
    The majority of ERC20 trading in centralized exchanges today is done with BTC and not ETH.
    Most decentralized exchanges offer only ETH/Token and not BTC/Token trades. Wrapped
    tokens can bridge this gap and provide more liquidity on decentralized exchanges. In addition,
    other decentralized applications/protocols (like funds, lending payments) will also benefit from
    having access to greater liquidity that a BTC token can bring. WBTC brings the ease of
    creation of smart contracts to Bitcoin.
    Benefits of fiat tokens
    Tokens backed by fiat currencies offer a safe way for traders to keep their money in a
    cryptocurrency without having to worry about price fluctuations. This is particularly useful for
    traders on both centralized and decentralized exchanges where there is no direct way of
    transferring fiat currencies. Fiat currency backed tokens also promise a world in which a

    cryptocurrency can replace traditional finance. Notably, it can be used in e-commerce by both
    buyer and seller without having to worry about conversion rates or taxes (buyers are required
    to pay capital gains tax calculated at the time of purchase in the US).
    Interoperability between cryptocurrencies
    As we see an expansion in the number of cryptocurrencies today, each one focuses on some
    aspect of monetary exchange. Some such aspects are transactional throughput, privacy,
    cheap transaction fees, smart contract ability, and decentralization of nodes/miners. The
    wrapped framework would make it easy to represent any other cryptocurrency, such as
    Bitcoin, on Ethereum and thereby enhance it with all the capabilities of the Ethereum
    blockchain. One such use case is the ability for initial coin offerings (ICOs) to be directly funded
    and mint tokens on deposits of wrapped Bitcoin tokens. In the future, centralized exchanges
    and other institutions which accept cryptocurrencies would not need to maintain multiple
    cryptocurrency nodes and instead could just develop on Ethereum.
    On chain ways to enforce policies
    Tokenization also provides a way to enforce policies on chain. On chain policy enforcement
    makes rules more transparent and doesn’t rely on one single party to enforce them. Based on
    the type of asset, there could be a need to enforce rules on asset transfer or trade. Securities
    for example require whitelisting, holding periods, and identity management.

    Key Roles
    ● Custodian - The institution or party who holds the asset. In the case of WBTC, this will
    be played by BitGo [4] . Custodians hold the keys to mint tokens.
    ● Merchant - The institution or party to which wrapped tokens will be minted to and burnt
    from. Merchants play a key role in distribution of the wrapped token. In the case of

    WBTC, this will be played initially by Kyber [5] and Republic Protocol [6] . Each merchant
    holds a key to initiate minting of new wrapped tokens and burning of wrapped tokens.
    ● User - The holders of the wrapped token. Users can use wrapped tokens to transfer
    and transact like any other ERC20 token in the Ethereum ecosystem.
    ● WBTC DAO member - Contract changes and addition/removal of custodians and
    merchants will be controlled by a multi-signature contract. Holders of the keys to the
    multi-sig contract will be held by institutions as part of the WBTC DAO.
    Custodians exchange assets for wrapped tokens with merchants. This is done through two
    different types of transactions; minting (creation of wrapped tokens) and burning (reducing
    supply of wrapped tokens). These transactions will be available publicly and can be viewed by
    anyone through a block explorer. After the initial exchange, merchants aim to maintain a buffer
    of wrapped tokens so that they can exchange it with users. The two-step minting process
    helps reduce the time it takes for users to get wrapped tokens, as minting and burning are
    more time consuming processes.

    Custodian wallet setup

    Custodians are expected to have a pooled wallet for all merchants. The wallet will use
    multi-signature with all keys controlled by the custodian. The wallet will only be able to send to
    the whitelisted merchant address on chain. All minting and burning transactions are expected
    to be done within 48 hours of submission to the custodian. Note that in case of multiple
    custodians, a single wallet might not have enough funds to redeem all pending wrapped


    Minting refers to the process of creating new wrapped tokens. Minting in the wrapped
    framework has to be done by a custodian, but needs to be “initiated” by a merchant. It is
    important to note that minting does not involve the user. It is a set of transactions done
    between the merchant and the custodian.

    Sequence of minting events for WBTC

    ● Merchant initiates a transaction to authorize the custodian to mint X WBTC to the
    merchant’s address on the Ethereum chain.
    ● The merchant sends the custodian X BTC.
    ● Custodian waits for 6 confirmations of the BTC transaction
    ● Custodian creates a transaction to mint X new WBTC tokens on the Ethereum chain

    Sequence of events for users to receive WBTC tokens

    ● User requests wrapped tokens from a merchant
    ● The merchant does the required AML, KYC procedures and gets identification
    information from the user
    ● The user and merchant perform an atomic swap , or use a trusted exchange with the
    merchant receiving Bitcoin and the user receiving WBTC
    Burning refers to the action of redeeming BTC for WBTC tokens. Only merchant addresses can
    burn wrapped tokens. In order to do so, the ‘burn’ function is called in the contract with the
    amount of tokens to be burnt on the Ethereum chain. By doing so, the amount is deducted
    from the merchant’s WBTC balance (on chain) and the supply of WBTC is reduced.

    Sequence of events for burning WBTC tokens

    ● The merchant creates a burn transaction, burning X WBTC tokens
    ● Custodian waits for 25 block confirmations of the ETH transaction
    ● Custodian releases X BTC to the merchants Bitcoin address
    ● Custodian makes an ethereum transaction marking the burn request as completed

    Sequence of events for users to receive Bitcoins

    ● User requests the redemption of tokens from a merchant
    ● The merchant does the required AML, KYC procedures and gets identification
    information from user
    ● The user and merchant perform an atomic swap , or use a trusted exchange where the
    user receives Bitcoin and the merchant receives WBTC tokens
    On Chain transfer restrictions
    Based on the token, there could be restrictions in place for the transfer of tokens. For WBTC,
    there will be no restrictions on transfers.


    The wrapped token contract is governed by a multisig contract in which signatures are
    required from DAO members in order to add/remove members. All custodians and merchants
    will be DAO members, but other institutions can also be included as a member without having
    a custodian or merchant role. An “M of N” signature signature will be used in the contract
    where M is the required number of signatures in the multisig contract and N is the total number
    of members. The values of M and N will be decided mutually between members keeping in
    mind security as well as the ease of adding/removing members.

    Side chain for wrapped tokens

    Initially, WBTC will be launched on the Ethereum mainnet chain. The mainnet chain is easily
    accessible and usable as there are a network of exchanges, block explorers, wallets, and other
    Dapps on it. One of the key benefits of tokenization, is cheap transactional cost. But with
    gaining popularity of Ethereum and increased Dapp creation, transaction costs of wrapped
    tokens could rise to the point where it is not cheap to do so on the main chain. The
    collaboration of multiple institutions in the wrapped framework enables the ability to deploy a
    practical scalable solution to increase transactional throughput.

    This can be done through the use of a pegged sidechain, using existing software ( parity-bridge )
    run among DAO members. The chain will run on it’s own proof of authority network [7] using
    the Aura consensus algorithm [8] . Blocks will be created every 4 seconds predictably and in a
    performant manner. Currently, there is already such a chain (Kovan testnet) and it has been in
    operation since March 2017. Wrapped tokens will be pegged between the main and side chain
    by creating a 2-way multi-sig wallet on mainnet and on the sidechain. Side chains provide
    much needed scalability on ethereum. Some benefits of a side chain for trading and
    transferring wrapped tokens are:
    ● Scaling with minimal development costs (same EVM)
    ● Dedicated, increased throughput - seperate blockchain on separate hardware and
    potential proof of authority (PoA) advantages (faster blocks)
    ● Easy to support in existing clients and wallets
    ● Chain is free from other “noisy neighbors”
    ● Minimal transactional cost (to prevent spam)
    Validators (block generators) will be chosen from wrapped partners and other trusted parties
    who will be geographically distributed and represent several different domiciles / governments.
    Validators will also maintain the 2-way peg between the main and side chain. To peg the value
    of wrapped tokens on both chains, we propose a multi-signature contract to be used on the
    mainnet and the sidechain.
    ● To send from Ethereum mainnet to Ethereum sidechain:
    ○ Send from mainnet address to the federated mainnet multi-sig address
    ■ It is recommended to send the amount while calling the
    “sendToSidechain” method on the multi-sig address, specifying as the
    argument the destination address on the sidechain
    ■ If sent without a method, the destination address on the sidechain will be
    assumed to be the same as the source address
    ○ An event is generated on the mainnet to record the send
    ○ Federated signers “lock” tokens on mainnet
    ○ After a “confirmation period”, multisig authorities on the sidechain can validate
    the send event on the mainnet and disburse the amount to the destination
    address on the sidechain, less transaction fees
    ● To send from ETH sidechain to ETH mainnet:
    ○ Identical (symmetric)
    WBTC will be the first asset on the sidechain and will use a combination of these components
    working together to create an ecosystem:
    ● Node Software and Configuration
    ● Block Explorer
    ● Wallet Providers

    ● Block Validators
    ● Multi-sig Authorities
    Transactions will be charged at the minimal starting gas price of 1 Gwei to cover running block
    validators and to prevent spam on the sidechain. Validators can also be incentivized off chain
    for each Dapp or have block rewards. Details of distribution/management of Ether on the
    sidechain are still to be determined.

    Atomic Swap

    Atomic swaps can be used between merchants and users in order to exchange WBTC and
    BTC. If the user would like to receive WBTC or BTC more quickly, a trusted method of
    exchange could also be done through the merchants.
    Once KYC is completed, the steps for users to atomically swap BTC for WBTC with the
    merchant are:
    ● User generates a secret and a hash of it is provided to the merchant off chain. The user
    and the merchant also agree on other swapping details such as receive addresses (ETH
    and BTC)
    ● The user creates a Bitcoin HTLC (Hashed Time Lock Contract) using the merchant’s
    Bitcoin address, user’s refund address, secret hash, and expiration time. This is used to
    create a P2SH address which the user funds with X BTC
    ● After 6 confirmations, the merchant will create an HTLC contract on Ethereum, by using
    the user’s Ethereum address, merchant’s refund address, secret hash, and expiration
    time. The merchant then transfers X WBTC to the atomic swap contract.
    ● The user reveals the secret in order to move X WBTC from the atomic swap contract to
    the user’s Ethereum address
    ● The merchant uses the secret in order to move Bitcoin funds from the P2SH address
    ● If the user does not claim the WBTC within the expiration time, the transaction does not
    go through and the user can claim the BTC back

    Some important things to note here:

    ● In order to deploy the atomic swap contract and send WBTC to it, there are transaction
    fees involved. Hence, the user will have to pay an atomic swap fee before initiating a
    ● Atomic swaps take time and multiple transactions on both the BTC and ETH chain. The
    user may have the option of doing a trusted swap in which BTC is transferred to the
    merchant address and after 6 confirmations on the bitcoin network, the merchant sends
    WBTC to the user. This involves trust in the merchant, but it is quicker and cheaper.

    WBTC vs Atomic Swaps

    Atomic swaps can be performed without WBTC for users which only want to perform a
    BTC-ETH trade. They can be done on a decentralized exchange outlined through a mechanism
    by the Komodo platform [9] . However, it is important to note that WBTC provides a
    representation of BTC on the ETH chain, which is required for DAPPs and the ecosystem to
    interact with. A few other tradeoffs to consider while comparing atomic swaps with WBTC:
    ● They require price discovery to be done by whoever does the atomic swap. In wrapped
    tokens price discovery only needs to be done while trading on a decentralized
    exchange after having already obtained WBTC.
    ● Requires atomic swap technology to be supported by existing wallets and
    decentralized exchanges. Wrapped BTC will be available for use in any ERC20
    supported wallet.
    ● They are really slow because every transactions is as slow as multiple confirmations on
    the ETH chain and then the Bitcoin chain (as opposed to WBTC, where the initial
    minting/tokenization is slow but after creation it’s easily tradable on the ETH chain)
    ● Doing an atomic swap on a decentralized exchange requires a separate deposit and a
    atomic swap fee as well. This is inconvenient each time users want to swap currencies.


    Transfers of WBTC between users will have no cost apart from network fees. There are three
    ways in which different parties in the network can earn fees:
    ● Custodian fees: This is taken by the custodian at the time when a merchant mints or
    burns wrapped tokens.
    ● Merchant fees: This is taken by the merchant who the user exchanges wrapped tokens
    with for the asset.
    ● Sidechain transaction fees: This fee is predominantly aimed at preventing spam on the
    sidechain. This is shared equally among all institutions running nodes on the sidechain.

    Legal Binding

    Contract between custodians and merchants
    The process of minting and burning tokens does not involve the user and is between trusted
    institutions. Merchants are required to hold the identity information of the user securely.
    Custodians are required to publish details of assets under custody quarterly and perform
    minting/burning duties in a timely manner. Failure to meet these criteria can lead to removal
    from the network.

    It is to be noted that there can be multiple custodians in the network, but this comes at the
    cost of increasing the risk involved in the network. A model where custodianship is shared by
    different institutions holding keys to a multi-sig wallet is also possible in the future. Though
    operationally, minting/burning/auditing would require more coordination and time. A security
    breach among any of the custodians would cause the loss of trust and could lead to mass
    withdrawals. A security breach with a merchant is much less severe as all outstanding tokens
    will still be backed up by custodians, but instead could lead to a loss of KYC/AML user data.

    Trust model

    In some sense custodians are trusted in the wrapped framework, as assets could be stolen or
    they might not honour the one-to-one backing. However, the wrapped framework aims to
    minimize this trust in a few ways:
    ● Quarterly audits will be conducted by external third parties to verify that all wrapped
    tokens minted have an equal amount of asset stored among all custodians. In the case
    of WBTC, proof of reserves can be shown by publishing signatures from the addresses
    which bitcoin is stored in.
    ● Custodians will not be able to mint tokens on their own, but would instead require the
    initiation of a merchant in order to do so. Hence creation of new tokens involves both
    the custodian and the merchant.
    ● The user is insulated from interacting with the custodian through a set of merchant
    institutions. An individual merchant does not need to be trusted, but instead all
    merchants together would need to be.
    ● Existing credibility of the institutions involved is at stake for all the institutions involved
    with the framework.


    There will be full transparency in the functioning of the wrapped token. All key details of the
    network will be reflected in a dashboard, some of which are:
    ● Names and details of institutions performing different roles in the network
    ● Status of mint and burn orders (pending, processing, cancelled, complete)
    ● Total amount of BTC stored by custodians
    ● Total amount of WBTC in the network (Will be the same or slightly lower than BTC
    ● Quarterly audits in the form of transactions which prove that the custodian has the keys
    to the Bitcoin
    ● Merchant and Custodians ethereum addresses
    ● The Bitcoin address associated with each merchant, controlled by the custodian
    ● Links to the open source token contract code / deployed contract on a block explorer

    An example of what the dashboard might look like:



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