Withdraw BTC

In a single transaction, the user removes some of their Bitcoin collateral from their vault while keeping the same amount of borrowed UNIT. This reduction in collateral increases the Bitcoin price at which liquidation would be triggered, moving it closer to the current price and reducing the user’s safety margin.

The user initiates a transaction to withdraw a portion of their BTC collateral from their vault UTXO. The MPC network verifies that the requested withdrawal maintains the required minimum collateralisation ratio for the existing borrowed UNIT position. The transaction builder then constructs a PSBT that separates the withdrawn BTC while retaining sufficient collateral in the vault. The outputs include the withdrawn BTC being returned to the user’s control and an updated vault UTXO with the reduced collateral amount.

In a second transaction, the new vault state is processed, paying the network fees for both transactions to ensure atomic execution. This generates an updated vault token reflecting the reduced collateral and new collateralisation ratio. The vault UTXO retains both the user update path and the guardian/oracle liquidation path, though with a smaller safety buffer due to the lower collateral level.

An OP_RETURN output records the updated vault state, including the decreased collateral and revised collateralisation ratio.

Withdraw BTC Transaction Diagram