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Ramps

Ramps are the mechanisms that allow users to onboard and exit from the Ark protocol with its own built-in mechanisms. They are designed to provide a seamless experience for users, allowing them to move funds in and out of Ark. There are two types of ramps:

Boarding​

The preferred method for onboarding funds into Ark is by sending Bitcoin to a boarding address. This is a specialized Taproot address where the internal key is disabled (no key-path spend) and the script path encodes two paths:

  • Unilateral Exit Path
    The user can spend the funds after a timeout without Operator cooperation.

  • Collaborative Path
    The user and the Operator can jointly spend the funds immediately.

Once the UTXO sent to a boarding address is confirmed on Bitcoin, Alice can register it with the Ark Operator. The Operator can then include it in a Commitment Transaction, establishing their VTXO within a Batch Output.

tip

Boarding addresses resemble VTXOs but typically use longer timelocks to reduce risk.

While any UTXO can be used as an input, a boarding address is the preferred way as it removes the risk of a malicious user double-spending the UTXO and replacing or failing the commitment transaction.

Exiting​

Once a user has a VTXO, Ark supports two exit mechanisms, both preserving user custody and Bitcoin-enforceability.

1. Unilateral Exit​

Users can unroll their VTXO into a native Bitcoin UTXO by broadcasting a chain of presigned virtual transactions. This requires:

  • Possession of the full unroll path for the VTXO
  • The corresponding Batch Output being confirmed and unexpired

This method does not require Operator cooperation and is always available before expiry.

2. Collaborative Exit​

Alternatively, users can exit Ark cooperatively by requesting the Ark Operator to convert their VTXO into a UTXO in a new Commitment Transaction.

  • The user registers their VTXO as input
  • The desired output is a Bitcoin UTXO (instead of a VTXO)
  • The Operator constructs and broadcasts the transaction

This method allows for immediate withdrawal with lower delay and is operationally simpler when the Operator is available.