Class LoanSigningHelper

Helper for LoanSet multi-party signing (XLS-66d). LoanSet requires two signatures: the broker (Account) signs as the submitter (TxnSignature), and the borrower (Counterparty) provides a CounterpartySignature (inner STObject with SigningPubKey + TxnSignature).

Three signing patterns (analogous to Batch V1/V2/V3):

V1 — Automatic (both keys available):

var result = LoanSigningHelper.SignLoanSet(loanTx, brokerWallet, borrowerWallet);
await client.SubmitRequest(result.TxBlob);

V2 — Parallel (keys on separate devices, sign independently):

// Device A (borrower):
var counterpartySig = borrowerWallet.SignAsLoanCounterparty(preparedTxJson);
// Device B (broker):
var brokerSig = brokerWallet.Sign(preparedTxJson);
// Combiner:
var combined = LoanSigningHelper.CombineLoanSignatures(brokerSig.TxBlob, counterpartySig.TxBlob);
await client.SubmitRequest(combined);

V3 — Sequential (borrower signs first, passes to broker):

// Borrower signs, adds CounterpartySignature:
var withCounterparty = borrowerWallet.SignAsLoanCounterparty(preparedTxJson);
// Broker receives the partially signed blob, adds TxnSignature:
var final = LoanSigningHelper.BrokerSign(withCounterparty.TxBlob, brokerWallet);
await client.SubmitRequest(final.TxBlob);

Multisig borrower (Counterparty with a SignerList): each signer of the borrower's list produces a portable Signer entry with the standard multisign call, and the composer places them under CounterpartySignature.Signers (rippled verifies them against the counterparty's SignerList over the same multisign preimage as tx.Signers). Autofill with the signer count so the fee covers them (rippled LoanSet::calculateBaseFee charges one base fee per counterparty signer):

var prepared = LoanSigningHelper.PrepareForSigning(await client.Autofill(loanTx.ToDictionary(), signersCount: 2), brokerWallet);
var brokerPart = brokerWallet.Sign(prepared);
var part1 = signer1.Sign(prepared, multisign: true);
var part2 = signer2.Sign(prepared, multisign: true);
// ledger-driven routing (looks up the Counterparty's SignerList):
var composed = await client.ComposeSignatures(new[] { brokerPart.TxBlob, part1.TxBlob, part2.TxBlob });
// or offline, naming the borrower's signers:
var offline = LoanSigningHelper.CombineLoanSignatures(new[] { brokerPart.TxBlob, part1.TxBlob, part2.TxBlob }, new[] { signer1.ClassicAddress, signer2.ClassicAddress });

Inheritance

object

LoanSigningHelper

Namespace: Xrpl.Wallet

Assembly: Xrpl.dll

Syntax

public static class LoanSigningHelper

Methods

BrokerSign(string, XrplWallet)

V3 — Broker signs a partially signed LoanSet blob (one that already has CounterpartySignature). Decodes the blob, strips CounterpartySignature to compute the correct preimage, adds the broker's TxnSignature, then restores CounterpartySignature for encoding.

Declaration

public static SignatureResult BrokerSign(string partiallySignedBlob, XrplWallet brokerWallet)

Parameters

Type	Name	Description
string	partiallySignedBlob	Hex blob from borrower's SignAsLoanCounterparty (has CounterpartySignature, no TxnSignature).
XrplWallet	brokerWallet	The broker's wallet (submitting account).

Returns

Type	Description
SignatureResult	Fully signed transaction blob and hash.

CombineLoanSignatures(IEnumerable<string>, IReadOnlyCollection<string>)

Combines a broker part with the portable Signer entries of a multisig borrower: entries from counterpartySignerAccounts land in CounterpartySignature.Signers, any other entry in tx.Signers (a multisig broker). Offline; for ledger-driven routing use IXrplClient.ComposeSignatures.

Declaration

public static SignatureResult CombineLoanSignatures(IEnumerable<string> partBlobs, IReadOnlyCollection<string> counterpartySignerAccounts)

Parameters

Type	Name	Description
IEnumerable<string>	partBlobs	The broker's blob and the borrower-side multisign parts.
IReadOnlyCollection<string>	counterpartySignerAccounts	Accounts of the borrower's SignerList.

Returns

Type	Description
SignatureResult

CombineLoanSignatures(string, string)

V2 — Combine independently signed broker and counterparty blobs. The broker blob has TxnSignature but no CounterpartySignature. The counterparty blob has CounterpartySignature but no TxnSignature.

Declaration

public static SignatureResult CombineLoanSignatures(string brokerSignedBlob, string counterpartySignedBlob)

Parameters

Type	Name	Description
string	brokerSignedBlob	Hex blob signed by the broker (has TxnSignature).
string	counterpartySignedBlob	Hex blob signed by the borrower (has CounterpartySignature).

Returns

Type	Description
SignatureResult	Combined fully signed blob.

PrepareForSigning(JsonObject, XrplWallet)

Prepares a LoanSet JSON object for signing.

Declaration

public static JsonObject PrepareForSigning(JsonObject txJson, XrplWallet brokerWallet)

Parameters

Type	Name	Description
JsonObject	txJson
XrplWallet	brokerWallet

Returns

Type	Description
JsonObject

PrepareForSigning(ITransactionRequest, XrplWallet)

Prepares a LoanSet transaction JSON for signing. Sets SigningPubKey to the broker's public key and removes signature fields. Returns a JsonObject ready for both parties to sign.

Declaration

public static JsonObject PrepareForSigning(ITransactionRequest loanSetTx, XrplWallet brokerWallet)

Parameters

Type	Name	Description
ITransactionRequest	loanSetTx	The LoanSet transaction (autofilled with Sequence, Fee, LastLedgerSequence).
XrplWallet	brokerWallet	The broker's wallet (submitting account).

Returns

Type	Description
JsonObject	JsonObject ready for signing by both parties.

Remarks

Fee for CounterpartySignature overhead is handled by Autofill (see CalculateBaseFeeForType in Autofill.cs).

SignLoanSet(JsonObject, XrplWallet, XrplWallet)

V1 — Automatic signing: both broker and borrower wallets available locally. Computes the signing preimage, has both parties sign, and returns the fully signed tx blob.

Declaration

public static SignatureResult SignLoanSet(JsonObject preparedTx, XrplWallet brokerWallet, XrplWallet borrowerWallet)

Parameters

Type	Name	Description
JsonObject	preparedTx	Prepared LoanSet JSON (from PrepareForSigning or already prepared).
XrplWallet	brokerWallet	The broker's wallet (submitting account).
XrplWallet	borrowerWallet	The borrower's wallet (counterparty).

Returns

Type	Description
SignatureResult	Fully signed transaction blob and hash.