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Messages and intents

Beyond transaction witnesses, the bindings expose two signature flavors with distinct verification rules: spending signatures (verified against a public key) and challenge signatures (verified against an address). Transaction intents build on challenge signatures.

Spending signatures​

signMessageForSpending(privateKey, message) signs an arbitrary message with a plain private key; verifySignatureForSpending(publicKey, signature, message) checks it against the matching public key. This is the flavor used by transaction witnesses.

import MintlayerWalletBindings

let message = Data("withdraw:123".utf8)
let signature = try signMessageForSpending(privateKey: key, message: message)
let ok = try verifySignatureForSpending(
    publicKey: publicKeyFromPrivateKey(privateKey: key),
    signature: signature,
    message: message)

Challenges​

signChallenge(privateKey, message) produces a signature that verifyChallenge checks against a bech32 address rather than a raw public key — useful when the verifier only knows the address (for example, proving control of a wallet address to a backend).

Transaction intents​

A transaction intent is an on-chain record that the signers of specific inputs approve of a given message. The flow:

  1. Build the message to sign: makeTransactionIntentMessageToSign(intent, transactionId) — intent is an arbitrary string, transactionId the hex id of the transaction that carries the intent.
  2. Sign that message once per input destination with signChallenge.
  3. Assemble: encodeSignedTransactionIntent(signedMessage, signatures) — one challenge signature per input, in input order.
  4. Verify: verifyTransactionIntent(expectedSignedMessage, encodedSignedIntent, inputDestinations, network).
import org.mintlayer.wallet.bindings.makeTransactionIntentMessageToSign
import org.mintlayer.wallet.bindings.signChallenge
import org.mintlayer.wallet.bindings.encodeSignedTransactionIntent

val message = makeTransactionIntentMessageToSign(intent, txIdHex)
val signatures = listOf(signChallenge(inputKey0, message))   // one per input destination
val signedIntent = encodeSignedTransactionIntent(message, signatures)

Multisig destinations​

encodeDestination(address, network) turns a bech32 address into a destination blob; encodeMultisigChallenge and multisigChallengeToAddress build and inspect multisig challenges (a signature-count threshold plus public keys). These are the building blocks for multisig destinations in outputs and witnesses.