Transaction signing and authorization

How signing and authorization work across Circle Wallets products, including who initiates and approves transactions, where keys live, and the transaction signing lifecycle.

How transactions are initiated and authorized depends on the wallet type you choose. The wallet type determines who controls signing (your backend or your users) and where keys live.

Who initiates and who approves transactions

Every onchain transaction must be initiated and authorized before it is broadcast. Initiating means requesting the transaction. Authorizing means approving the signing. The following table shows who handles each and where keys are held for each wallet type.

Wallet type	Who initiates	Who authorizes	Keys
Developer-controlled	Your backend (API/SDK). Your users can also initiate a request from your app after you authenticate them and assign a wallet.	Your backend, using the entity secret.	MPC. You hold the entity secret. Circle hosts MPC nodes, or you host them (for example, on-premises).
User-controlled	Your app calls user APIs or SDKs (client or server) for the signed-in end user.	Your user, by authenticating in your app. Circle cannot sign without your user’s approval.	MPC. Only your user can complete signing.
Modular	Your app (SDK), on behalf of your user.	Your user (passkey). Circle cannot sign without your user’s approval. The passkey never leaves your user’s device.	Passkey on your user’s device (or cloud backup).

For details on how keys are secured (MPC and passkeys), see Key management.

Transaction signing lifecycle

1. Initiate: A client (your backend or your app) calls Circle APIs to create a transaction signing request (for example, transfer, contract call).
2. Authorize: The party that controls the key approves the signing. In developer-controlled wallets, your backend approves using the entity secret. In user-controlled and modular wallets, your user authenticates using a confirmation UI, PIN, or biometrics, and approves in your app.
3. Sign: Circle (with MPC or passkey participation) produces the signature.
4. Broadcast: The signed transaction is sent to the blockchain. For supported blockchains, Circle can handle broadcasting, or you can choose to use the signing APIs with your own node.

Submitted vs finalized

Sending a transaction to the blockchain (submitted) and the blockchain processing it to finality (complete) are two separate events. Circle’s API response does not indicate finality. State changes (for example, sent, confirmed, failed) are delivered asynchronously. Set up Webhook notifications to receive them.