begin

This action initiates a sequence of step actions.

Parameters

• ${\Pi }_{C_{zeos},\Omega ,X}$: A proof bundle validating all zactions within this EOSIO/Antelope transaction
• $\mathsf{tx}$: A sequence of EOSIO/Antelope actions to be executed within this EOSIO/Antelope transaction
• $\mathsf{note}{\mathsf{s}}_{\mathsf{enc}}$: A sequence of encrypted UTXO ciphertexts to be added to the Transmitted UTXO Ciphertext List as part of the In-band secret distribution of UTXOs

Flow

The following steps specify the flow of 'begin'.

Step 0

The 'begin' action is called as part of an EOSIO/Antelope transaction.

Step 1

The currently executing EOSIO/Antelope transaction is scanned by looping through all actions contained in this transaction. The following checks are performed:

• There is only one 'begin' action within the entire EOSIO/Antelope transaction
• The number of 'step' actions within the transaction equals the number of actions contained in the sequence $\mathsf{tx}$ passed as parameter
• The sequence of 'step' actions is continuous and succeed the 'begin' action

Step 2

Loop through all actions within the sequence $\mathsf{tx}$ and perform the following steps:

• Is this action whitelisted by the ZEOS smart contract? If $\mathsf{false}$: cancel execution
• Does this action depend on a sequence of zactions? If $\mathsf{true}$:
  • Loop through all zactions of this action and collect public inputs $x$ by adding them to the set of public inputs $X$

Step 3

Verify the Halo2 proof bundle ${\Pi }_{C_{zeos},\Omega ,X}$ with the set of public inputs $X$ collected in the previous step. If proof verification fails, cancel execution.

Step 4

Check if the number of encrypted UTXO ciphertexts in $\mathsf{note}{\mathsf{s}}_{\mathsf{enc}}$ matches the number of expected UTXO ciphertexts based on the zactions in this transaction. If so, add the sequence $\mathsf{note}{\mathsf{s}}_{\mathsf{enc}}$ to the global set of Transmitted UTXO Ciphertext List.

Step 5

Add all UTXO commitments ${\mathsf{CM}}_B$ and ${\mathsf{CM}}_C$ contained in the set of public inputs $X$ which are not related to authenticator tokens to the Commitment Tree. Add the new root of the tree to the Commitment Tree Root Set.

Step 6

Copy the sequence of EOSIO/Antelope actions $\mathsf{tx}$ into the ZEOS smart contract's transaction buffer. This is a singleton which buffers the sequence of actions, \mathsf{tx}, for actual execution in the upcoming 'step' actions.