DA-03 · LESSON 01

Open a vault

KEY DEFINITIONS

Terms used in this lesson

Vault: A set of Bitcoin outputs and spending rules that holds collateral and represents the current loan state.
Oracle: A system that reports outside information, such as a market price, for use by a protocol.
PSBT: Partially Signed Bitcoin Transaction: a format for passing an unsigned or partly signed transaction between constructors and signers.
Guardian: A Ducat policy-checking signer that can authorize or reject defined protocol transactions.
BTC: The common market ticker for bitcoin.
UNIT: Ducat’s dollar-pegged stablecoin, the asset a borrower can create against bitcoin collateral.
UTXO: Unspent transaction output: one discrete chunk of bitcoin that can be used as a transaction input.
Collateral: An asset pledged against a debt; it can be used to cover the debt if agreed conditions are breached.
Runes: A Bitcoin metaprotocol that assigns fungible-token meaning to transaction outputs through off-chain interpretation.
Identifier: Identifier: a value used to distinguish one request, object, or participant from another.
Runestone: Transaction data interpreted by the Runes protocol to describe token creation or allocation.
Transaction ID: The identifier produced by hashing a Bitcoin transaction’s non-witness serialization.
Validator: Software or a participant that independently checks state transitions under a system's rules. The exact role depends on the protocol being discussed.

The client fetches protocol and oracle data, reserves issuance capacity, builds and signs PSBTs, and submits the request for Guardian validation and co-signing.

35 min Difficulty 4/5 Not started

VISUAL MODEL

See the whole mechanism before going step by step

Use the diagrams to orient yourself. Then the guided explanation below teaches every part in depth.

4 explanatory views

CONCEPT-SPECIFIC MAP · ducat vault stateA vault transition spends one anchored state and creates its successorSelect any state to inspect its exact role.

RELATIONSHIP MAPInputs, rule, and outputs

01
PREDECESSOROutpoint V0: collateral 1 BTC, debt 40k UNIT
The current vault is anchored to a specific spendable Bitcoin output and reconstructed metadata.
02
ACTIONDeposit 0.2 BTC
The requested action selects its own allowed state transition.
03
PRICE CHECKBTC = 100k UNIT
A versioned price commitment supplies the value used for collateral calculations.
04
RATIO120k / 40k = 300%
Collateral increases while debt stays unchanged.
05
SUCCESSORV1: 1.2 BTC, 40k debt
The old outpoint is spent atomically; validators accept only a correctly formed successor.

Rule shown: The transaction must satisfy Bitcoin spending rules while Ducat validation reconstructs collateral, debt, profile, and action-specific invariants.

STAGE 1 OF 5PREDECESSOR: Outpoint V0: collateral 1 BTC, debt 40k UNIT

The current vault is anchored to a specific spendable Bitcoin output and reconstructed metadata.

Governing relationship: The transaction must satisfy Bitcoin spending rules while Ducat validation reconstructs collateral, debt, profile, and action-specific invariants. Complete path: 1. PREDECESSOR, Outpoint V0: collateral 1 BTC, debt 40k UNIT. The current vault is anchored to a specific spendable Bitcoin output and reconstructed metadata. 2. ACTION, Deposit 0.2 BTC. The requested action selects its own allowed state transition. 3. PRICE CHECK, BTC = 100k UNIT. A versioned price commitment supplies the value used for collateral calculations. 4. RATIO, 120k / 40k = 300%. Collateral increases while debt stays unchanged. 5. SUCCESSOR, V1: 1.2 BTC, 40k debt. The old outpoint is spent atomically; validators accept only a correctly formed successor.

1. State transitionWhat exists, what changes, and what results

BEFORE

Use an illustrative 25,000 UNIT opening debt and 42,000 UNIT issuance account. This vector is different from required practice and does not claim current limits.

MECHANISM

The client loads the active protocol settings, UNIT Rune ID, oracle price contract, Guardian key, funding UTXOs, collateral amount, requested debt, and output postage. Output…

AFTER

After the displayed confirmation depth, validators reconstruct the UNIT output, successor account, and new vault. Required practice uses a separate server-executed vector.

Text equivalent: Starting from Use an illustrative 25,000 UNIT opening debt and 42,000 UNIT issuance account. This vector is different from required practice and does not claim current limits. The mechanism begins when The client loads the active protocol settings, UNIT Rune ID, oracle price contract, Guardian key, funding UTXOs, collateral amount, requested debt, and output postage. Output postage is the small bitcoin amount attached… The resulting lesson is After the displayed confirmation depth, validators reconstruct the UNIT output, successor account, and new vault. Required practice uses a separate server-executed vector.

2. Mechanism pathSelect a stage to inspect its job

STAGE 1 OF 4

Gather fixed inputs

The client loads the active protocol settings, UNIT Rune ID, oracle price contract, Guardian key, funding UTXOs, collateral amount, requested debt, and output postage. Output postage is the small bitcoin amount attached to a token-bearing or metadata-bearing output so that it is a real Bitcoin output.

Complete path: 1. Gather fixed inputs: The client loads the active protocol settings, UNIT Rune ID, oracle price contract, Guardian key, funding UTXOs, collateral amount, requested debt, and output postage. Output postage is the small bitcoin amount attached to a token-bearing or metadata-bearing output so that it is a real Bitcoin output. 2. Build the issue parent: An issuance account supplies UNIT through a runestone allocation. 3. Build the vault child: The dependent transaction locks collateral in the new vault output and commits the owner, Guardian, oracle, and action metadata. 4. Sign in layers: Wallet inputs and protocol-controlled inputs receive their required signatures before the pair is broadcast in dependency order.

3. Rule and failure boundaryWhat accepts the result and where it can stop

ACCEPTED PATH

The worked case executes the named inputs and checks in the displayed order. Wallet inputs and protocol-controlled inputs receive their required signatures before the pair is broadcast in dependency order.

CHANGED CONDITION

A missing, malformed, stale, unauthorized, or inconsistent required input stops at its first named boundary. It is a signed two-transaction Bitcoin workflow whose confirmed outputs are later reconstructed as UNIT and vault state.

Important distinction: Opening a vault is one database request that immediately creates spendable UNIT. It is a signed two-transaction Bitcoin workflow whose confirmed outputs are later reconstructed as UNIT and vault state.

Text equivalent: The accepted path is enforced by The worked case executes the named inputs and checks in the displayed order. Wallet inputs and protocol-controlled inputs receive their required signatures before the pair is broadcast in dependency order. If the required condition changes, A missing, malformed, stale, unauthorized, or inconsistent required input stops at its first named boundary. It is a signed two-transaction Bitcoin workflow whose confirmed outputs are later reconstructed as UNIT and vault state.

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Learn the idea

Opening creates a new vault UTXO, the Bitcoin output that represents the loan state. An issuance account is a Guardian-controlled Bitcoin output that carries the protocol's current UNIT issuance capacity. The captured builder spends that account in an issue transaction, then builds a dependent vault transaction that locks collateral and creates the initial debt state.

GUIDED EXPLANATION1/4 ideas inspected

Gather fixed inputs

The worked example follows the explanation

Inspect every idea above to open it.

Important distinction“Opening a vault is one database request that immediately creates spendable UNIT.”

It is a signed two-transaction Bitcoin workflow whose confirmed outputs are later reconstructed as UNIT and vault state.

FINISH LEARNING FIRST

The questions unlock after every required learning activity

Inspect every guided idea, open the worked example, rebuild its mechanism, and complete the deterministic lesson tool. Your progress is saved automatically.