Ark Taproot Scripts

Script tree

Ark virtual transaction outputs (VTXO) are created by a shared output. This output is enforcing the value to be splitted into a binary tree of other taproot scripts.

graph TD
    A[Shared Out ROOT]
    A --> B[Shared out 1]
    A --> C[Shared out 2]
    B --> D[Shared out 3]
    B --> E[Shared out 4]
    C --> F[Shared out 5]
    C --> G[Shared out 6]
    D --> H((VTXO 1))
    E --> I((VTXO 2))
    F --> J((VTXO 3))
    G --> K((VTXO 4))

Each node of the diagram is a taproot script.

Shared output script

A shared output is a bitcoin transaction output locked by a taproot script with 2 tapscript closures:

• Unroll and Boarding scripts use Elements introspections opcodes to force the spending transaction format. The tx creates the next level of the script tree on-chain. Splitting the value into 2 outputs with the children taproot scripts.
• Sweep lets the Ark Service Provider to spend the whole shared output after a timeout (CSV).

VTXO script

A VTXO taproot script is the last level of the script tree. It should appear on-chain only if the VTXO owner decided to unilaterally exit the Ark. It has 2 tapscript closures:

• Redeem lets to spend the VTXO onchain after a CSV delay. the delay prevents the ASP to lost a VTXO spent off-chain.
• Forfeit expects both parties (owner and ASP) to sign the spending transaction. It is used to spend the VTXO off-chain.

Miniscript

The scripts are written using miniscript syntax. You can analyse them using the Elements Miniscript compiler.

install the miniscript-compiler:

cargo install miniscript-compiler

Compile miniscript examples:

make unroll 
make onboarding
make vtxo