dlcspecs/Transactions.md

DLC Transactions

A Note on Key Derivation

There is no strict constraint on how the two keys (Funding and ToLocal) and one address (Final Address) used in a DLC are generated. We do note that absent external considerations, it does seem reasonable to use BIP 44 with three sequential address indices. We think this will usually be the best option for implementing key derivation because it is compatible with normal wallet account discovery.

Funding Transaction

Known Values

• Local Funding Inputs: List[TransactionInput]
• Local Change ScriptPubKey: ScriptPubKey
• Local Funding Public Key: ECPublicKey
• Remote Funding Inputs: List[TransactionInput]
• Remote Change ScriptPubKey: ScriptPubKey
• Remote Funding Public Key: ECPublicKey
• nLockTime: UInt32
• Total Local Collateral: CurrencyUnit
• Total Remote Collateral: CurrencyUnit
• Fee Rate: FeeUnit

Where

• Local something something Remote
• The sum of each Funding Inputs' value is at least that of its Total Collateral
• Funding Public Keys are both 33-byte compressed public keys
• nLockTime is in the past (rather than just using 0)
  • for privacy purposes and also to prevent fee snipping
• Both Change ScriptPubKeys must be either P2WSH/P2WPKH, or P2SH-P2WSH/P2SH-P2WPKH

Global

• nLockTime

Inputs

• Local Funding Inputs
• Remote Funding Inputs

Outputs

• P2WSH(DLC Funding Output)
• Local Change ScriptPubKey
• Remote Change ScriptPubKey

Where

• P2WSH(DLC Funding Output)'s value is Total Local Collateral + Total Remote Collateral + Computed CET Fee + Computed ToLocal Closing Fee

• DLC Funding Output's script is

  OP_2 <Local Funding Public Key> <Remote Funding Public Key> OP_2 OP_CHECKMULTISIG
  

• Each Change ScriptPubKey's value is at most that of its respective Sum(Funding Inputs) - Total Collateral - Computed Fees - (Computed CET Fee + Computed ToLocal Closing Fee)/2 with Computed Fees being proportional to each party's total input weight and Computed CET Fee being the estimated fee for a Contract Execution Transaction and Computed ToLocal Closing Fee being the estimated fee for a Unilateral Closing Transaction

Contract Execution Transaction

Known Values

• Oracle Signature Point: ECPublicKey
• Local Funding Public Key: ECPublicKey
• Local CET ToLocal Public Key: ECPublicKey
• Local Payout: CurrencyUnit
• Remote CET ToLocal Public Key: ECPublicKey
• Remote Final Address: BitcoinAddress
• Remote Payout: CurrencyUnit
• nLockTime: UInt32
• Timeout: UInt32
• DLC Funding Output: ScriptPubKey
• Fee Rate: FeeUnit

Where

• Oracle Signature Point is the 33-byte public key associated with this CET's outcome
• Local Funding Public Key is the local key from the funding transaction
• Both CET Public Keys are 33-byte compressed public keys
• Local Paytout + Remote Payout = (DLC Funding Output).value
• nLockTime is set to the contract maturity time
• Timeout is a CSV locktime after which penalty transactions are valid
• DLC Funding Output is of the form specified above

Global

• nLockTime

Inputs

• Input Spending(P2WSH(DLC Funding Output))

Outputs

• P2WSH(ToLocalOutput)
• ToRemoteOutput

Where

• P2WSH(ToLocalOutput).value = Local Payout + Computed ToLocal Closing Fee

• ToRemoteOutput.value = Remote Payout

• ToLocalOutput's script is:

  OP_IF
    <Oracle Signature Point + Local Funding Public Key + SHA256(Local CET ToLocal Public Key)*G>
  OP_ELSE
    <Timeout> OP_CHECKSEQUENCEVERIFY OP_DROP
    <Remote CET ToLocal Public Key>
  OP_ENDIF
  OP_CHECKSIG
  

  • Note that The addition in the if case is elliptic curve point addition

• ToRemoteOutput's script corresponds to Remote CET Final Address

Refund Transaction

Known Values

• Local Final Address: BitcoinAddress
• Total Local Collateral: CurrencyUnit
• Remote Final Address: BitcoinAddress
• Total Remote Collateral: CurrencyUnit
• Timeout: UInt32
• DLC Funding Output: ScriptPubKey
• Fee Rate: FeeUnit

Where

• Unlike CETs in a DLC, there is only one Refund Transaction that both parties share, similar to how there is only one Funding Transaction
• Total Local Collateral + Total Remote Collateral = (DLC Funding Output).value
• Timeout is a CLTV locktime set well after the contract maturity time
• DLC Funding Output is of the form specified above

Global

• nLockTime is Timeout

Inputs

• Input Spending(P2WSH(DLC Funding Output))

Outputs

• ToLocalOutput
• ToRemoteOutput

Where

• ToLocalOutput's value is Total Local Collateral + RefundFeeDelta/2

• ToRemoteOutput's value is Total Remote Collateral + RefundFeeDelta/2

• RefundFeeDelta = Computed CET Fee + Computed ToLocal Closing Fee - Computed Refund Tx Fee (note that the Refund Transaction is smaller than any CET)

• ToLocalOutput's script is that of Local Final Address

• ToRemoteOutput's script is that of Remote Final Address

Mutual Closing Transaction

Known Values

• Local Final Address: BitcoinAddress
• Local Payout: CurrencyUnit
• Remote Final Address: BitcoinAddress
• Remote Payout: CurrencyUnit
• nLockTime: UInt32
• DLC Funding Output: ScriptPubKey
• Fee Rate: FeeUnit

Where

• After the contract maturity time, Mutual Closing Transaction is created in cooperation for fee reduction and improvement in privacy
• Local Payout = (Contract Execution Transaction Local Payout).value
• Remote Payout = (Contract Execution Transaction Remote Payout).value
• nLockTime is in the past (rather than just using 0)
  • for privacy purposes and also to prevent fee snipping
• DLC Funding Output is of the form specified above

Global

• nLockTime

Inputs

• Input Spending(P2WSH(DLC Funding Output))

Outputs

• ToLocalOutput
• ToRemoteOutput

Where

• ToLocalOutput's value is Local Payout + MutualClosingFeeDelta/2

• ToRemoteOutput's value is Remote Payout + MutualClosingFeeDelta/2

• MutualClosingFeeDelta = Computed CET Fee + Computed ToLocal Closing Fee - Computed MutualClosing Tx Fee (note that the Mutual Closing Transaction is smaller than any CET)

• ToLocalOutput's script is that of Local Final Address

• ToRemoteOutput's script is that of Remote Final Address

Closing Transaction (Unilateral)

Known Values

• Local Final Address: BitcoinAddress
• nLockTime: UInt32
• Local Payout: CurrencyUnit
• ToLocalOutput: ScriptPubKey
• Fee Rate: FeeUnit

Where

• ToLocalOutput is of the form specified above
• nLockTime is in the past (rather than just using 0)
  • for privacy purposes and also to prevent fee snipping

Global

• nLockTime

Inputs

• Input Spending(P2WSH(ToLocalOutput))

Outputs

• One output corresponding to Local Final Address with value Local Payout

Closing Transaction (Penalty)

Known Values

• Local Address: BitcoinAddress
• nLockTime: UInt32
• Remote's ToLocalOutput: ScriptPubKey
• Fee Rate: FeeUnit

Where

• Local Address is any unused local address
• Remote's ToLocalOutput is of the form specified above
• nLockTime is in the past (rather than just using 0)
  • for privacy purposes and also to prevent fee snipping

Global

• nLockTime

Inputs

• Input Spending(P2WSH(Remote's ToLocalOutput))

Outputs

• One output corresponding to LocalAddress with value P2WSH(Remote's ToLocalOutput).value - fee