Issue¶

Overview¶

The Issue module allows as user to create new interBTC tokens. The user needs to request interBTC through the requestIssue function, then send BTC to a Vault, and finally complete the issuing of interBTC by calling the executeIssue function. If the user does not complete the process in time, the Vault can cancel the issue request and receive a griefing collateral from the user by invoking the cancelIssue function. Below is a high-level step-by-step description of the protocol.

Step-by-step¶

Precondition: a Vault has locked collateral as described in the Vault Registry.
A user executes the requestIssue function to open an issue request. The issue request includes the amount of interBTC the user wants to issue, the selected Vault, and a small collateral reserve to prevent Griefing.
A user sends the equivalent amount of BTC to issue as interBTC to the Vault on the Bitcoin blockchain.
The user or Vault acting on behalf of the user extracts a transaction inclusion proof of that locking transaction on the Bitcoin blockchain. The user or a Vault acting on behalf of the user executes the executeIssue function on the BTC Parachain. The issue function requires a reference to the issue request and the transaction inclusion proof of the Bitcoin locking transaction. If the function completes successfully, the user receives the requested amount of interBTC into his account.
Optional: If the user is not able to complete the issue request within the predetermined time frame (IssuePeriod), the Vault is able to call the cancelIssue function to cancel the issue request adn will receive the griefing collateral locked by the user.

Security¶

Unique identification of Bitcoin payments: On-Chain Key Derivation Scheme

Vault Registry¶

The data access and state changes to the Vault registry are documented in Fig. 7 below.

Fig. 7 The issue protocol interacts with three functions in the Vault Registry that handle updating the different token balances.¶

Fee Model¶

Issue fees are paid by users in interBTC when executing the request. The fees are transferred to the Parachain Fee Pool.
If an issue request is executed, the user’s griefing collateral is returned.
If an issue request is canceled, the Vault assigned to this issue request receives the griefing collateral.

Data Model¶

Scalars¶

IssuePeriod¶

The time difference between when an issue request is created and required completion time by a user. Concretely, this period is the amount by which ActiveBlockCount is allowed to increase before the issue is considered to be expired. The period has an upper limit to prevent griefing of Vault collateral.

IssueBtcDustValue¶

The minimum amount of BTC that is required for issue requests; lower values would risk the rejection of payment on Bitcoin.

Maps¶

IssueRequests¶

Users create issue requests to issue interBTC. This mapping provides access from a unique hash IssueId to a Issue struct. <IssueId, Issue>.

Structs¶

Issue¶

Stores the status and information about a single issue request.

Parameter	Type	Description
`vault`	AccountId	The address of the Vault responsible for this issue request.
`opentime`	BlockNumber	The ActiveBlockCount when the issue request was created.
`period`	BlockNumber	Value of the IssuePeriod when the request was made.
`griefingCollateral`	DOT	Security deposit provided by a user.
`amount`	interBTC	Amount of interBTC to be issued.
`fee`	interBTC	Fee charged to the user for issuing.
`requester`	AccountId	User account receiving interBTC upon successful issuing.
`btcAddress`	BtcAddress	Vault’s P2WPKH Bitcoin deposit address.
`btcPublicKey`	BtcPublicKey	Vault’s Bitcoin public key used to generate the deposit address.
`btcHeight`	u32	The highest recorded height of the relay at time of opening.
`status`	Enum	Status of the request: Pending, Completed or Cancelled.

Functions¶

requestIssue¶

A user opens an issue request to create a specific amount of interBTC. When calling this function, a user provides their parachain account identifier, the to be issued amount of interBTC, and the Vault she wants to use in this process (parachain account identifier). Further, she provides some (small) amount of DOT collateral (griefingCollateral) to prevent griefing.

Specification¶

Function Signature

requestIssue(requester, amount, vault, griefingCollateral)

Parameters

requester: The user’s account identifier.
amount: The amount of interBTC to be issued.
vault: The address of the Vault involved in this issue request.
griefingCollateral: The collateral amount provided by the user as griefing protection.

Events

RequestIssue

Preconditions

The function call MUST be signed by requester.
The BTC Parachain status in the Security component MUST NOT be SHUTDOWN:2.
The BTC-Relay MUST be initialized.
The Vault MUST be registered and active.
The amount MUST be greater than or equal to IssueBtcDustValue.
The griefingCollateral MUST exceed or equal the value of request amount at the current exchange-rate, multiplied by IssueGriefingCollateral.
The griefingCollateral MUST be equal or less than the requester’s free balance.
The tryIncreaseToBeIssuedTokens function MUST return a new BTC deposit address for the Vault ensuring that the Vault’s free collateral is above the SecureCollateralThreshold for the requested amount and that a unique BTC address is used for depositing BTC.
A new unique issuedId MUST be generated via the generateSecureId function.

Postconditions

The Vault’s toBeIssuedTokens MUST increase by amount.
The requester’s free balance MUST decrease by griefingCollateral.
The requester’s locked balance MUST increase by griefingCollateral.
A new BTC deposit address for the Vault MUST be generated by the tryIncreaseToBeIssuedTokens.
The new issue request MUST be created as follows:
- issue.vault: MUST be the vault.
- issue.opentime: MUST be the ActiveBlockCount of the current block of this transaction.
- issue.period: MUST be the current IssuePeriod.
- issue.griefingCollateral: MUST be the griefingCollateral amount passed to the function.
- issue.amount: MUST be amount minus issue.fee.
- issue.fee: MUST equal amount multiplied by IssueFee.
- issue.requester: MUST be the requester
- issue.btcAddress: MUST be the BTC address returned from the tryIncreaseToBeIssuedTokens
- issue.btcPublicKey: MUST be the BTC public key returned from the tryIncreaseToBeIssuedTokens
- issue.btcHeight: MUST be the current Bitcoin height as stored in the BTC-Relay.
- issue.status: MUST be Pending.
The new issue request MUST be inserted into IssueRequests using the generated issueId as the key.

executeIssue¶

An executor completes the issue request by sending a proof of transferring the defined amount of BTC to the vault’s address.

Specification¶

Function Signature

executeIssue(executorId, issueId, rawMerkleProof, rawTx)

Parameters

executor: the account of the user.
issueId: the unique hash created during the requestIssue function.
rawMerkleProof: Raw Merkle tree path (concatenated LE SHA256 hashes).
rawTx: Raw Bitcoin transaction including the transaction inputs and outputs.

Events

ExecuteIssue
IssueAmountChange

Preconditions

The function call MUST be signed by executor.
The BTC Parachain status in the Security component MUST NOT be SHUTDOWN:2.
The issue request for issueId MUST exist in IssueRequests.
The issue request for issueId MUST NOT have expired.
The rawTx MUST be valid and contain a payment to the Vault.
The rawMerkleProof MUST be valid and prove inclusion to the main chain.
If the amount transferred is less than issue.amount + issue.fee, then the executor MUST be the account that made the issue request.

Postconditions

If the amount transferred IS less than the issue.amount + issue.fee:
- The Vault’s toBeIssuedTokens MUST decrease by the deficit (issue.amount - amountTransferred).
- The Vault’s free balance MUST increase by the griefingCollateral * (1 - amountTransferred / (issue.amount + issue.fee)).
- The requester’s free balance MUST increase by the griefingCollateral * amountTransferred / (issue.amount + issue.fee).
- The issue.fee MUST be updated to the amount transferred multiplied by the IssueFee.
- The issue.amount MUST be set to the amount transferred minus the updated issue.fee.
If the amount transferred IS NOT less than the expected amount:
- The requester’s free balance MUST increase by the griefingCollateral.
- If the amount transferred IS greater than the expected amount:
  If the Vault IS NOT liquidated and has sufficient collateral:
  
  The Vault’s toBeIssuedTokens MUST increase by the surplus (amountTransferred - issue.amount).
  
  The issue.fee MUST be updated to the amount transferred multiplied by the IssueFee.
  
  The issue.amount MUST be set to the amount transferred minus the updated issue.fee.
  
  If the Vault IS NOT liquidated and does not have sufficient collateral:
  
  There MUST exist a Refund request which references issueId.
The requester’s locked balance MUST decrease by issue.griefingCollateral.
The issue.status MUST be set to Completed.
The Vault’s toBeIssuedTokens MUST decrease by issue.amount + issue.fee.
The Vault’s issuedTokens MUST increase by issue.amount + issue.fee.
The user MUST receive issue.amount interBTC in its free balance.
Function distributeReward MUST complete successfully - parameterized by issue.fee.

cancelIssue¶

If an issue request is not completed on time, the issue request can be cancelled.

Specification¶

Function Signature

cancelIssue(requester, issueId)

Parameters

requester: The sender of the cancel transaction.
issueId: the unique hash of the issue request.

Events

CancelIssue

Preconditions

The function call MUST be signed by requester.
The BTC Parachain status in the Security component MUST NOT be SHUTDOWN:2.
The issue request for issueId MUST exist in IssueRequests.
The issue request MUST have expired.

Postconditions

If the vault IS liquidated:
- The requester’s free balance MUST increase by the griefingCollateral.
If the Vault IS NOT liquidated:
- The vault’s free balance MUST increase by the griefingCollateral.
The requester’s locked balance MUST decrease by the griefingCollateral.
The vault’s toBeIssuedTokens MUST decrease by issue.amount + issue.fee.
The issue status MUST be set to Cancelled.

Events¶

RequestIssue¶

Emit an event if a user successfully open a issue request.

Event Signature

RequestIssue(issueId, requester, amount, fee, griefingCollateral, vault, btcAddress, btcPublicKey)

Parameters

issueId: A unique hash identifying the issue request.
requester: The user’s account identifier.
amount: The amount of interBTC requested.
fee: The amount of interBTC to mint as fees.
griefingCollateral: The security deposit provided by the user.
vault: The address of the Vault involved in this issue request.
btcAddress: The Bitcoin address of the Vault.
btcPublicKey: The Bitcoin public key of the Vault.

Functions

requestIssue

IssueAmountChange¶

Emit an event if the issue amount changed for any reason.

Event Signature

IssueAmountChange(issueId, amount, fee, griefingCollateral)

Parameters

issueId: A unique hash identifying the issue request.
amount: The amount of interBTC requested.
fee: The amount of interBTC to mint as fees.
griefingCollateral: Confiscated griefing collateral.

Functions

executeIssue

ExecuteIssue¶

Event Signature

ExecuteIssue(issueId, requester, amount, vault, fee)

Parameters

issueId: A unique hash identifying the issue request.
requester: The user’s account identifier.
amount: The amount of interBTC issued to the user.
vault: The address of the Vault involved in this issue request.
fee: The amount of interBTC minted as fees.

Functions

executeIssue

CancelIssue¶

Event Signature

CancelIssue(issueId, requester, griefingCollateral)

Parameters

issueId: the unique hash of the issue request.
requester: The sender of the cancel transaction.
griefingCollateral: The released griefing collateral.

Functions

cancelIssue

Error Codes¶

ERR_VAULT_NOT_FOUND

Message: “There exists no Vault with the given account id.”
Function: requestIssue
Cause: The specified Vault does not exist.

ERR_VAULT_BANNED

Message: “The selected Vault has been temporarily banned.”
Function: requestIssue
Cause: Issue requests are not possible with temporarily banned Vaults

ERR_INSUFFICIENT_COLLATERAL

Message: “User provided collateral below limit.”
Function: requestIssue
Cause: User provided griefingCollateral below IssueGriefingCollateral.

ERR_UNAUTHORIZED_USER

Message: “Unauthorized: Caller must be associated user”
Function: executeIssue
Cause: The caller of this function is not the associated user, and hence not authorized to take this action.

ERR_ISSUE_ID_NOT_FOUND

Message: “Requested issue id not found.”
Function: executeIssue
Cause: Issue id not found in the IssueRequests mapping.

ERR_COMMIT_PERIOD_EXPIRED

Message: “Time to issue interBTC expired.”
Function: executeIssue
Cause: The user did not complete the issue request within the block time limit defined by the IssuePeriod.

ERR_TIME_NOT_EXPIRED

Message: “Time to issue interBTC not yet expired.”
Function: cancelIssue
Cause: Raises an error if the time limit to call executeIssue has not yet passed.

ERR_ISSUE_COMPLETED

Message: “Issue completed and cannot be cancelled.”
Function: cancelIssue
Cause: Raises an error if the issue is already completed.