VTXO
Also · Virtual UTXO · Round · Refresh
A VTXO, virtual UTXO, is Ark’s unit of ownership. It is a leaf in a tree of pre-signed Bitcoin transactions, spendable off-chain and redeemable on-chain, but only until it expires.
A VTXO looks like a UTXO to its owner but does not exist on the blockchain. It is backed by a chain of pre-signed transactions descending from a shared output, which the operator and the users signed in advance and nobody broadcasts. Spending it off-chain creates a new VTXO for the recipient, co-signed by the operator, in seconds.
The catch is time. Each VTXO carries an expiry, after which the operator can sweep the shared output. Before that, the wallet must either refresh it in a round, which renews its lifetime, or exit on-chain. A payment received out of round also assumes, until the next refresh, that the sender and the operator do not collude. Wallets automate all of this, and the user mostly needs to come online now and then.
In French · VTXO
