# EIP 712 Type Definitions

All EIP-712 types used by Lynx writes. The Domain is shared across both signing methods.

## Domain

```json
{
  "name": "UniX",
  "version": "1",
  "chainId": 1
}
```

EIP-712 domain type: `EIP712Domain(string name,string version,uint256 chainId)` — no `verifyingContract`.

## Method A — Agent (Default)

Used by every write endpoint except the four in Method B.

```
Agent(address sender, bytes32 actionHash, uint64 nonce, uint64 expiresAfter)
```

See [Signing Method A](file:///authentication-and-signing/signing-method-a) for how `actionHash` is computed.

## Method B — Direct Typed Structs

Used by the four account-relationship endpoints.

### ApproveAgent

```
ApproveAgent(address sender, address agentAddress, address authorizedAddress,
             uint32 validDays, string label, uint64 nonce, uint64 expiresAfter)
```

### RevokeAgent

```
RevokeAgent(address sender, address agentAddress, uint64 nonce, uint64 expiresAfter)
```

### RenewAgent

```
RenewAgent(address sender, address agentAddress, uint32 validDays, uint64 nonce, uint64 expiresAfter)
```

### CreateSubAccount

```
CreateSubAccount(address sender, string label, uint64 nonce, uint64 expiresAfter)
```

## Type Encoding Rules

| Solidity type | Encoded as                                                   |
| ------------- | ------------------------------------------------------------ |
| `address`     | 20 bytes, right-aligned in a 32-byte slot, left-zero-padded. |
| `uint32`      | 4 bytes big-endian, right-aligned in a 32-byte slot.         |
| `uint64`      | 8 bytes big-endian, right-aligned in a 32-byte slot.         |
| `bytes32`     | Used as-is.                                                  |
| `string`      | `keccak256(utf8_bytes(value))` (32 bytes).                   |

## `signing_hash` Formula

```
typeHash      = keccak256(encodeType_string)
structHash    = keccak256(typeHash ‖ encoded_field_1 ‖ encoded_field_2 ‖ …)
domainSeparator = keccak256(
    keccak256("EIP712Domain(string name,string version,uint256 chainId)")
    ‖ keccak256("UniX")
    ‖ keccak256("1")
    ‖ pad32(chainId)
)
signing_hash  = keccak256("\x19\x01" ‖ domainSeparator ‖ structHash)
```

The `signing_hash` is both the input to ECDSA signing and the on-chain `tx_hash`.

## Reference Implementations

| Language          | Library       | Function                                                                          |
| ----------------- | ------------- | --------------------------------------------------------------------------------- |
| Python            | `eth_account` | `encode_typed_data(domain, types, primaryType, message)` → `Account.sign_message` |
| Node / TypeScript | `ethers` v6   | `wallet.signTypedData(domain, types, message)`                                    |
| Go                | `go-ethereum` | `signer/core/apitypes` + `crypto.Sign`                                            |
| Rust              | `ethers-rs`   | `LocalWallet::sign_typed_data`                                                    |

See [Signing Method A](file:///1548985/authentication-and-signing/signing-method-a.md) and [Signing Method B](file:///1548985/authentication-and-signing/signing-method-b.md) for full Python + Node code samples.


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