Authorization Fundamentals

Learn EIP-7702 authorization structure, delegation, and account abstraction

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Conceptual Guide - For API reference and method documentation, see Authorization API.

EIP-7702 authorizations enable Externally Owned Accounts (EOAs) to temporarily delegate code execution to smart contracts. This guide teaches authorization fundamentals using Tevm.

What is EIP-7702 Authorization?

An authorization is a signed message allowing an EOA to temporarily set its code pointer to a smart contract’s code for a single transaction. After the transaction, the EOA reverts to its normal state.

Key Characteristics:

• Temporary - Delegation lasts only one transaction
• Signed - EOA owner must explicitly sign authorization
• Per-transaction - Included in transaction’s authorization list
• Non-invasive - EOA retains original balance, nonce, storage

Why EIP-7702 Exists

The Account Abstraction Problem

Traditional EOAs have limitations:

• Can’t batch operations (need multiple transactions)
• Can’t sponsor gas (user always pays)
• Can’t implement custom validation logic
• Can’t recover if keys are lost

Contract wallets solve these but require:

• Migrating funds to new contract address
• Losing original EOA identity
• CREATE2 deployment complexity

EIP-7702 enables account abstraction without migration - your EOA gains smart contract capabilities on demand.

Use Cases

1. Sponsored Transactions - Relayer pays gas, user signs authorization
2. Batch Operations - Multiple token approvals, swaps, transfers in one transaction
3. Social Recovery - Guardian-based recovery without moving funds
4. Session Keys - Temporary signing keys for games, dApps
5. Custom Validation - Multi-sig, time locks, spending limits

Authorization Structure

An authorization contains 6 fields:

type Authorization = {
  chainId: bigint;      // Chain ID where valid (prevents replay)
  address: Address;     // Contract to delegate to (20 bytes)
  nonce: bigint;        // Account nonce (prevents replay)
  yParity: number;      // Signature Y parity (0 or 1)
  r: bigint;            // Signature r value (32 bytes)
  s: bigint;            // Signature s value (32 bytes)
};

Field Details

chainId - Prevents cross-chain replay attacks. Authorization signed for mainnet (1) is invalid on Optimism (10).

address - The smart contract that will execute in your EOA’s context. Choose trusted contracts only.

nonce - Your EOA’s current nonce. Prevents replaying old authorizations.

yParity, r, s - secp256k1 signature components proving you authorized this delegation.

Delegation Mechanics

Before Authorization

EOA (0x742d...)
├── Balance: 10 ETH
├── Nonce: 5
├── Code: None (empty)
└── Storage: None (empty)

During Transaction with Authorization

EOA (0x742d...) [Delegated to 0xABCD...]
├── Balance: 10 ETH          (unchanged)
├── Nonce: 5 → 6             (incremented)
├── Code: → Points to 0xABCD (temporary)
└── Storage: Still empty     (contract uses its own storage)

Execution Context:

• Calls to EOA address execute delegated contract’s code
• msg.sender in delegated contract is the transaction sender
• address(this) is the EOA address
• Contract reads/writes its own storage (NOT EOA’s storage)

After Transaction

EOA (0x742d...)
├── Balance: 9.8 ETH (gas deducted)
├── Nonce: 6         (incremented)
├── Code: None       (reverted)
└── Storage: None    (unchanged)

Delegation is removed. EOA returns to normal state.

Authorization Lifecycle

1. Create Unsigned Authorization

Define what to delegate and where:

import * as Authorization from 'tevm/Authorization';

const unsigned = {
  chainId: 1n,                          // Mainnet
  address: '0xABCD....',               // Trusted batch executor contract
  nonce: 0n                            // Your current nonce
};

2. Sign Authorization

EOA owner signs with their private key:

const privateKey = Bytes32(); // Your private key

const auth = Authorization.sign.call(unsigned, privateKey);

console.log(auth);
// {
//   chainId: 1n,
//   address: Uint8Array(20),
//   nonce: 0n,
//   yParity: 1,
//   r: 12345...n,
//   s: 67890...n
// }

What Happens:

1. RLP-encodes [chainId, address, nonce]
2. Prepends EIP-7702 magic byte (0x05)
3. Keccak256 hashes the result
4. Signs hash with secp256k1
5. Returns authorization with signature fields

3. Include in Transaction

Authorization list is added to EIP-7702 transaction:

const transaction = {
  type: 0x04,                           // EIP-7702 transaction type
  chainId: 1n,
  nonce: 0n,
  maxFeePerGas: 20_000_000_000n,
  maxPriorityFeePerGas: 1_000_000_000n,
  gasLimit: 500_000n,
  to: batchExecutorAddress,             // Contract to call
  value: 0n,
  data: encodedBatchCalldata,
  authorizationList: [auth]             // Our signed authorization
};

// Sign and send transaction
const signedTx = signTransaction(transaction, senderPrivateKey);
await sendRawTransaction(signedTx);

4. Processing at Execution

When transaction executes:

1. Validate - Check signature, nonce, chain ID
2. Recover Authority - Extract EOA address from signature
3. Set Code Delegation - Point authority’s code to delegated address
4. Deduct Gas - Charge authorization processing costs
5. Execute Transaction - Run transaction with delegated code active
6. Revert Delegation - Remove code pointer after transaction

Complete Example: Sponsored Transaction

User wants to swap tokens but has no ETH for gas. Relayer sponsors the transaction.

Step 1: User Creates Authorization

import * as Authorization from 'tevm/Authorization';

// User's EOA: 0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb2
// Sponsor contract: 0x1234567890123456789012345678901234567890

const userPrivateKey = Bytes32(); // User's key
const userNonce = 0n; // Current nonce from chain

// User delegates to sponsor contract
const unsigned = {
  chainId: 1n,
  address: '0x1234567890123456789012345678901234567890', // Sponsor contract
  nonce: userNonce
};

const auth = Authorization.sign.call(unsigned, userPrivateKey);

// User sends auth to relayer (no transaction sent yet)

Step 2: Relayer Builds Transaction

// Relayer receives authorization from user
const receivedAuth = auth;

// Validate before using
Authorization.validate.call(receivedAuth);

// Calculate gas cost
const isEmpty = false; // Assuming sponsor contract exists
const authGas = Authorization.getGasCost.call(receivedAuth, isEmpty);

// Build transaction
const transaction = {
  type: 0x04,
  chainId: 1n,
  nonce: relayerNonce,
  maxFeePerGas: 30_000_000_000n,
  maxPriorityFeePerGas: 2_000_000_000n,
  gasLimit: 300_000n + authGas,         // Transaction gas + auth gas
  to: receivedAuth.address,             // Call sponsor contract
  value: 0n,
  data: encodeSwapCall(                 // Sponsor contract executes swap
    userTokenAddress,
    dexAddress,
    swapAmount
  ),
  authorizationList: [receivedAuth]
};

// Relayer signs and pays for transaction
const signedTx = signTransaction(transaction, relayerPrivateKey);
await sendRawTransaction(signedTx);

Step 3: Execution Flow

1. Transaction received by network
2. Process authorization:
   a. Verify signature → Recover authority (user's EOA)
   b. Check nonce matches user's current nonce
   c. Set user EOA code → sponsor contract code
   d. Deduct authorization gas

3. Execute transaction:
   a. Call sponsor contract (at user's EOA address)
   b. Sponsor contract verifies user authorized this action
   c. Sponsor contract executes swap on behalf of user
   d. Relayer pays all gas costs

4. Transaction completes:
   a. User EOA nonce incremented
   b. Code delegation removed
   c. Relayer charged gas fees
   d. User receives swapped tokens (paid no gas)

Step 4: Verify Authority

Relayer can verify who authorized the delegation:

const authority = Authorization.verify.call(receivedAuth);
console.log(`Authorized by: ${authority}`);
// "Authorized by: 0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb2"

// Check this matches expected user
if (authority !== expectedUserAddress) {
  throw new Error('Authorization from wrong address');
}

Security Considerations

What Can Be Delegated

Safe to delegate:

• Code execution logic
• Transaction batching
• Gas payment
• Custom validation rules

Cannot be delegated:

• Private keys (always remain with EOA owner)
• Existing ETH balance (stays in EOA)
• Existing storage (remains unchanged)
• Permanent account state

Authority vs Sender

Understand the difference:

contract SponsorContract {
  function executeSwap(address token, address dex) external {
    address authority = address(this);  // EOA that delegated
    address sender = msg.sender;        // Relayer who sent transaction

    // Authority owns the tokens
    IERC20(token).transferFrom(authority, dex, amount);

    // Sender pays gas
    // (gas deducted from sender's balance)
  }
}

Authority - EOA that signed authorization (owns assets) Sender - Address that sent transaction (pays gas)

Signature Validation

Always validate before processing:

import * as Authorization from 'tevm/Authorization';

function processAuthorization(auth: unknown) {
  // Type guard
  if (!Authorization.isItem(auth)) {
    throw new Error('Invalid authorization format');
  }

  // Structure validation
  Authorization.validate.call(auth);

  // Verify signer
  const authority = Authorization.verify.call(auth);

  // Check authority is expected/whitelisted
  if (!trustedAuthorities.has(authority)) {
    throw new Error('Unauthorized authority');
  }

  // Check nonce (prevent replay)
  const currentNonce = await provider.getTransactionCount(authority);
  if (auth.nonce !== currentNonce) {
    throw new Error('Nonce mismatch');
  }

  // Safe to process
  return processValidAuth(auth, authority);
}

Nonce Management

Nonces prevent replay attacks:

// Wrong: Using old nonce
const auth = Authorization.sign.call({
  chainId: 1n,
  address: contractAddress,
  nonce: 0n  // If user's nonce is now 5, this will fail
}, privateKey);

// Correct: Fetch current nonce
const currentNonce = await provider.getTransactionCount(userAddress);
const auth = Authorization.sign.call({
  chainId: 1n,
  address: contractAddress,
  nonce: currentNonce  // Use actual current nonce
}, privateKey);

Chain ID Validation

Prevent cross-chain replay:

// Authorization signed for mainnet
const mainnetAuth = {
  chainId: 1n,
  address: contractAddress,
  nonce: 0n
  // ... signature ...
};

// This will FAIL on Optimism (chainId: 10)
// Authorization's chainId must match network's chainId

Delegated Contract Trust

Only delegate to trusted contracts:

// Dangerous: Unknown contract
const unsafeAuth = {
  chainId: 1n,
  address: '0xUNKNOWN...', // Could drain your tokens
  nonce: 0n
};

// Safe: Verified contract
const safeAuth = {
  chainId: 1n,
  address: verifiedSponsorContract, // Audited, trusted
  nonce: 0n
};

Why this matters: Delegated contract executes with full access to authority’s assets for that transaction.

Gas Implications

Authorization Processing Costs

Each authorization costs gas to process:

import * as Authorization from 'tevm/Authorization';

// Base cost: 12,500 gas per authorization
const BASE_COST = 12_500n;

// Empty account cost: 25,000 gas (if delegated contract doesn't exist yet)
const EMPTY_ACCOUNT_COST = 25_000n;

// Calculate cost
const auth = { /* ... */ };
const isEmpty = false; // Contract exists at delegated address

const gasCost = Authorization.getGasCost.call(auth, isEmpty);
console.log(`Authorization gas: ${gasCost}`);
// 12,500 gas (base only, since not empty)

// For new contract:
const newContractAuth = { /* ... */ };
const isNewEmpty = true;

const newGasCost = Authorization.getGasCost.call(newContractAuth, isNewEmpty);
console.log(`New contract authorization gas: ${newGasCost}`);
// 37,500 gas (12,500 base + 25,000 empty)

Multiple Authorizations

Transaction can include multiple authorizations:

const authList = [auth1, auth2, auth3];

// Calculate total cost
const emptyAccounts = [false, true, false]; // Second is empty account
const totalGas = Authorization.calculateGasCost.call(authList, emptyAccounts);

console.log(`Total authorization gas: ${totalGas}`);
// 50,000 gas (12,500 * 3 + 25,000 * 1 empty)

// Add to transaction gas limit
transaction.gasLimit = executionGas + totalGas;

Gas Optimization Tips

1. Reuse existing contracts - Avoid empty account cost (25k gas)
2. Minimize authorization count - Each costs 12.5k gas minimum
3. Batch operations - Use one authorization for multiple actions
4. Cache validation - Don’t validate same authorization multiple times

// Inefficient: 3 authorizations = 37,500 gas minimum
const swap1 = createAuth(swapContract1);
const swap2 = createAuth(swapContract2);
const swap3 = createAuth(swapContract3);

// Efficient: 1 authorization = 12,500 gas
const batchAuth = createAuth(batchContract); // Contract handles all 3 swaps

Visual Flow Diagrams

Authorization Creation Flow

User Wallet                    Authorization Library
    |                                  |
    |------ unsigned data -----------→ |
    |     (chainId, address, nonce)    |
    |                                  |
    |                                  | RLP encode
    |                                  | Add magic byte (0x05)
    |                                  | Keccak256 hash
    |                                  |
    |←------ signing hash ------------  |
    |                                  |
    | Sign with private key            |
    |                                  |
    |------ signature (y, r, s) ------→|
    |                                  |
    |                                  | Combine with unsigned data
    |                                  |
    |←------ complete authorization -- |
    |    (chainId, address, nonce,     |
    |     yParity, r, s)               |

Transaction Execution Flow

Relayer                    Network                  EOA State
  |                          |                         |
  |--- Submit transaction ---|                         |
  |    (with authList)       |                         |
  |                          |                         |
  |                          | Validate authorization  |
  |                          | - Check signature       |
  |                          | - Verify nonce          |
  |                          | - Check chainId         |
  |                          |                         |
  |                          |-------- Set code -------|
  |                          |         delegation      |
  |                          |                         |
  |                          |                    Code → 0xABCD
  |                          |                         |
  |                          | Execute transaction     |
  |                          | (delegated code active) |
  |                          |                         |
  |                          | Transaction completes   |
  |                          |                         |
  |                          |------ Remove code ------|
  |                          |       delegation        |
  |                          |                         |
  |                          |                    Code → None
  |                          |                         |
  |←----- Transaction -------|                         |
  |       receipt            |                         |

Sponsored Transaction Flow

User                 Relayer              Network              Smart Contract
 |                     |                     |                       |
 |-- Create auth ------|                     |                       |
 |   (signs)           |                     |                       |
 |                     |                     |                       |
 |------ Send auth ----|                     |                       |
 |                     |                     |                       |
 |                     | Build transaction  |                       |
 |                     | (relayer pays gas) |                       |
 |                     |                     |                       |
 |                     |--- Submit tx -------|                       |
 |                     |   (with authList)   |                       |
 |                     |                     |                       |
 |                     |                     | Process authorization |
 |                     |                     | Set user EOA → contract|
 |                     |                     |                       |
 |                     |                     |------ Call contract --|
 |                     |                     |                       |
 |                     |                     |                       | Execute
 |                     |                     |                       | on behalf
 |                     |                     |                       | of user
 |                     |                     |                       |
 |                     |                     |←------ Result --------|
 |                     |                     |                       |
 |                     |                     | Remove delegation     |
 |                     |                     | Deduct gas from relayer|
 |                     |                     |                       |
 |                     |←---- Receipt -------|                       |
 |                     |                     |                       |
 |←---- Confirm -------|                     |                       |

Signing Hash Calculation

Understanding how the signing hash is computed:

import * as Authorization from 'tevm/Authorization';

const unsigned = {
  chainId: 1n,
  address: '0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb2',
  nonce: 0n
};

// Calculate signing hash
const hash = Authorization.hash.call(unsigned);

console.log(`Signing hash: 0x${[...hash].map(b =>
  b.toString(16).padStart(2, '0')
).join('')}`);

Process:

1. RLP Encode - [chainId, address, nonce]

   RLP([1, "0x742d...", 0])
   

2. Prepend Magic Byte - 0x05 || rlpEncoded

   0x05 + RLP_DATA
   

3. Keccak256 Hash

   keccak256(0x05 || RLP_DATA)
   

4. Result - 32-byte signing hash

This hash is what gets signed with secp256k1 to produce (yParity, r, s).

Authority Recovery

Extract the EOA address that signed an authorization:

import * as Authorization from 'tevm/Authorization';

const auth = {
  chainId: 1n,
  address: contractAddress,
  nonce: 0n,
  yParity: 1,
  r: 12345678901234567890n,
  s: 98765432109876543210n
};

// Recover authority (signer)
const authority = Authorization.verify.call(auth);
console.log(`Signed by: ${authority}`);

// Process authorization result
const result = Authorization.process.call(auth);
console.log(`Authority: ${result.authority}`);
console.log(`Delegated to: ${result.delegatedAddress}`);

How it works:

1. Recalculate signing hash from (chainId, address, nonce)
2. Use ecrecover with (hash, yParity, r, s) to extract public key
3. Hash public key with keccak256 and take last 20 bytes
4. Result is the EOA address (authority)

Batch Processing

Process multiple authorizations efficiently:

import * as Authorization from 'tevm/Authorization';

const authList = [auth1, auth2, auth3];

// Process all at once
const results = Authorization.processAll.call(authList);

results.forEach((result, index) => {
  console.log(`Authorization ${index}:`);
  console.log(`  Authority: ${result.authority}`);
  console.log(`  Delegated to: ${result.delegatedAddress}`);
});

// Calculate total gas
const emptyAccounts = [false, true, false];
const totalGas = Authorization.calculateGasCost.call(authList, emptyAccounts);
console.log(`Total gas cost: ${totalGas}`);

Comparison: Traditional vs EIP-7702

Scenario: User Wants to Swap 3 Tokens

Traditional EOA:

Transaction 1: Approve Token A
Transaction 2: Approve Token B
Transaction 3: Approve Token C
Transaction 4: Execute multi-token swap

Total: 4 transactions, ~300k gas total, user pays all gas

EIP-7702:

Create authorization (off-chain)
Relayer submits 1 transaction:
  - Authorization processed (12.5k gas)
  - Batch contract executes all approvals + swap (~200k gas)

Total: 1 transaction, ~212k gas total, relayer pays gas

Benefits:

• Fewer transactions (1 vs 4)
• Better UX (no gas for user)
• Atomic execution (all or nothing)
• Lower total gas cost

Resources

Specifications

• EIP-7702: Set EOA Account Code - Full specification
• EIP-2718: Typed Transaction Envelope - Transaction type framework
• EIP-191: Signed Data Standard - Signature format

Related Topics

• Account Abstraction - ERC-4337 alternative approach
• Transaction Types - Tevm transaction documentation
• Signature Verification - secp256k1 cryptography
• RLP Encoding - Recursive Length Prefix encoding

Next Steps

• Overview - Type definition and complete API reference
• Validation - Authorization structure validation
• Signing - Create and verify signatures
• Gas Calculations - Calculate processing costs
• Processing - Process authorization lists