# Core Concepts

Before starting to use BlockATM, please understand the following core concepts.

## Smart Contract Address Roles

BlockATM smart contracts involve three key address roles:

| Role                 | Description                                            | Permissions                        |
| -------------------- | ------------------------------------------------------ | ---------------------------------- |
| **Owner Address**    | Address that created the contract                      | Manage contract configuration      |
| **Signer Address**   | Address authorized to withdraw funds from the contract | Withdraw funds to Receiver address |
| **Receiver Address** | Address where funds ultimately arrive                  | Receive funds                      |

### Permission Relationship Diagram

```mermaid
graph TB
    Owner[Owner Address<br/>Creates Contract] -->|Manage| Contract[Smart Contract]
    Signer[Signer Address<br/>Signs for Withdrawal] -->|Authorize Withdrawal| Contract
    Contract -->|Transfer In| Receiver[Receiver Address<br/>Collection Address]

    style Owner fill:#e1f5ff
    style Signer fill:#fff4e1
    style Contract fill:#ffe1e1
    style Receiver fill:#e1f5ff
```

{% hint style="warning" %}
**Security Reminder**: It is recommended to use hardware wallets to manage Owner and Signer addresses to ensure fund security. Once the contract is deployed, Owner and Receiver addresses typically cannot be modified.
{% endhint %}

## Authorization Mechanism

### What is Authorization (Approval)?

Authorization is a standard ERC20 operation on the blockchain that allows one address (such as your payout contract) to spend your tokens on your behalf.

```
User --[Authorize]--> Payout Contract --[Withdraw]--> Recipient
```

### Authorization Payout vs Balance Payout

BlockATM supports two payout modes:

| Mode                 | Description                  | Use Case                               |
| -------------------- | ---------------------------- | -------------------------------------- |
| **Balance Payout**   | Pay using contract balance   | When contract has sufficient funds     |
| **Allowance Payout** | Pay using user authorization | Save Gas, no need to pre-fund contract |

### Authorization Payout Flow

```mermaid
sequenceDiagram
    participant User as User Wallet
    participant Contract as Payout Contract
    participant Token as Token Contract

    User->>Token: approve(contract address, amount)
    Token-->>User: Authorization successful

    User->>Contract: Submit payout request
    Contract->>Token: transferFrom(user, recipient, amount)
    Token->>Token: Verify authorization amount
    Token-->>Contract: Transfer successful
```

{% hint style="info" %}
**V5.8.0 New Feature**: V5.8.0 supports any address authorizing the payout contract, no longer requiring a whitelist.
{% endhint %}

## Networks and Tokens

### Supported Networks

| Network  | Token Standard | Characteristics          |
| -------- | -------------- | ------------------------ |
| TRON     | TRC-20         | Medium fees, fast speed  |
| Ethereum | ERC-20         | Most extensive ecosystem |
| Arbitrum | ERC-20         | Low fees, fast speed     |

### Common Tokens

| Token | Network       | Contract Address |
| ----- | ------------- | ---------------- |
| USDT  | TRC-20/ERC-20 | -                |
| USDC  | ERC-20        | -                |

## Glossary

| Term                     | Description                                                 |
| ------------------------ | ----------------------------------------------------------- |
| **Gas**                  | Blockchain network fee                                      |
| **Nonce**                | Transaction sequence number, used to prevent replay attacks |
| **Block Confirmation**   | Number of blocks that have confirmed the transaction        |
| **On-Chain Transaction** | Transaction that actually occurs on the blockchain          |


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