Transactions

Transactions in the AIBlock system are structured similarly to those found in Bitcoin. They consist primarily of a reference to a previous spendable amount on the blockchain (for AIBlock, this can be tokens or items (data assets) ) and a reference to an address to send the spendable amount to. To accomplish this, the spender is required to verify that they are the original owner of the spendable amount through public key signature schemes.

Structure

In the codebase, a transaction is structured as follows:

pub struct Transaction {
    pub inputs: Vec<TxIn>,
    pub outputs: Vec<TxOut>,
    pub version: usize,
    pub druid_info: Option<DdeValues>,
}

The attributes we care about for ownership verification are inputs and outputs, corresponding to the TxIn and TxOut data structures respectively.

Inputs

The inputs to a transaction are codified in the TxIn data structure:

pub struct TxIn {
    pub previous_out: Option<OutPoint>,
    pub script_signature: Script,
}

where the OutPoint referenced in previous_out:

pub struct OutPoint {
    pub t_hash: String,
    pub n: i32,
}

OutPoint has a t_hash corresponding to the hash of the previous spendable transaction in the blockchain. Within the script_signature attribute, we find a transaction execution script that defines how the spendable amount should actually be spent. Included in all script_signature entries is at least one signature which matches the public key of the spendable transaction already in the blockchain.

Outputs

The outputs of a transaction are codified in the TxOut data structure:

pub struct TxOut {
    pub value: Asset,
    pub locktime: u64,
    pub drs_block_hash: Option<String>,
    pub script_public_key: Option<String>,
}

Here we'll focus on the script_public_key, which is the public key that the owner of the transaction needs to use and sign with in order to spend the amount in the future.

Signing

In the AIBlock system, to tie the TxIn of the current transaction to the TxOut of the previous one, the user needs to sign the hash of the OutPoint referencing that TxOut. This ensures that spending a TxOut amount is impossible without:

• (A) The OutPoint referencing a specific TxOut
• (B) The user having the private key corresponding to the TxOut's public key
• (C) Being able to sign with the private key to on-spend the tokens