Timelock pattern in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Timelock pattern in blockchain?

The Timelock pattern is a security method that delays the execution of a transaction or contract change for a set time, allowing users to review and react before it happens.

beginner

Why is the Timelock pattern important in smart contracts?

It prevents sudden changes or attacks by giving users time to notice and respond, increasing trust and safety in decentralized systems.

intermediate

How does a Timelock contract typically work?

It stores a proposed action and a timestamp. The action can only be executed after the delay period passes, ensuring a waiting time before changes take effect.

intermediate

What is a common use case for the Timelock pattern?

Governance changes in decentralized protocols, where proposals are delayed to allow community review and prevent rushed decisions.

beginner

Name one risk if a Timelock pattern is not used in contract upgrades.

Without a Timelock, attackers or admins could make instant harmful changes, leaving no time for users to react or protect their assets.

What does the Timelock pattern delay in blockchain?

A Mining of new blocks

B Execution of transactions or contract changes

C User wallet creation

D Network synchronization

The Timelock pattern delays the execution of transactions or contract changes to provide a safety window.

Why is a delay important in the Timelock pattern?

A To reduce gas fees

B To speed up transactions

C To allow users to review and react

D To increase block size

The delay gives users time to notice and respond to proposed changes.

Which of these is a typical use of the Timelock pattern?

A Block validation

B Instant token transfers

C Wallet password reset

D Governance proposal execution

Governance proposals often use Timelock to delay execution for community review.

What happens if a Timelock is not used for contract upgrades?

A Changes can happen instantly, risking security

B Upgrades become impossible

C Users get free tokens

D Network speed increases

Without Timelock, instant changes can be harmful and leave no reaction time.

How does a Timelock contract know when to execute an action?

A After a set delay time has passed

B Immediately after proposal

C When a user logs in

D When the network is busy

The contract waits until the delay time expires before executing the action.

Explain the Timelock pattern and why it is used in blockchain smart contracts.

Think about how delaying changes helps protect users.

Describe a real-life scenario where the Timelock pattern improves safety in a decentralized system.

Consider how communities decide on important changes.

Practice

1.

What is the main purpose of the Timelock pattern in blockchain smart contracts?

easy

A. To delay certain actions until a specific time has passed

B. To speed up transaction processing

C. To encrypt user data

D. To reduce gas fees

Solution

1. Step 1: Understand the Timelock pattern concept

   The Timelock pattern is designed to delay actions in smart contracts until a set time has passed.

2. Step 2: Identify the purpose of the delay

   This delay helps protect users by preventing instant changes that could be harmful or unexpected.

3. Final Answer:

   To delay certain actions until a specific time has passed -> Option A

4. Quick Check:

   Timelock pattern = delay actions [OK]

Hint: Timelock means waiting before action happens [OK]

Common Mistakes:

• Thinking it speeds up transactions
• Confusing with encryption
• Assuming it lowers gas fees

2.

Which of the following Solidity code snippets correctly enforces a timelock using block.timestamp?

function execute() public {
  require(__________, "Too early to execute");
  // action code
}

easy

A. block.timestamp >= unlockTime

B. block.timestamp < unlockTime

C. block.number >= unlockTime

D. block.difficulty > unlockTime

Solution

1. Step 1: Understand the condition for timelock

   The action should only execute if the current time is equal or after the unlock time.

2. Step 2: Choose the correct comparison

   Using block.timestamp >= unlockTime ensures the function runs only after the unlock time.

3. Final Answer:

   block.timestamp >= unlockTime -> Option A

4. Quick Check:

   Time check uses block.timestamp >= unlockTime [OK]

Hint: Use block.timestamp and >= for timelock checks [OK]

Common Mistakes:

• Using < instead of >=
• Using block.number instead of block.timestamp
• Using unrelated block properties

3.

What will be the output of the following Solidity function call if block.timestamp is 1650000000 and unlockTime is 1650000100?

function canExecute() public view returns (bool) {
  return block.timestamp >= unlockTime;
}

medium

A. true

B. Revert with error

C. Compilation error

D. false

Solution

1. Step 1: Compare block.timestamp and unlockTime values

   Given block.timestamp = 1650000000 and unlockTime = 1650000100, block.timestamp is less than unlockTime.

2. Step 2: Evaluate the return statement

   The expression block.timestamp >= unlockTime evaluates to false.

3. Final Answer:

   false -> Option D

4. Quick Check:

   1650000000 >= 1650000100 = false [OK]

Hint: Compare timestamps carefully for true/false output [OK]

Common Mistakes:

• Assuming >= means true when timestamp is smaller
• Confusing block.timestamp with block.number
• Expecting errors instead of boolean

4.

Identify the error in this Solidity timelock function and choose the fix:

uint256 public unlockTime;

function execute() public {
  require(block.timestamp > unlockTime, "Too early");
  // perform action
}

medium

A. Use block.number instead of block.timestamp

B. Change block.timestamp > unlockTime to block.timestamp >= unlockTime

C. Remove the require statement

D. Change unlockTime to block.timestamp

Solution

1. Step 1: Analyze the require condition

   The condition block.timestamp > unlockTime disallows execution exactly at unlockTime.

2. Step 2: Adjust condition to allow execution at unlockTime

   Changing to block.timestamp >= unlockTime allows execution starting from unlockTime.

3. Final Answer:

   Change block.timestamp > unlockTime to block.timestamp >= unlockTime -> Option B

4. Quick Check:

   Use >= to include unlockTime moment [OK]

Hint: Use >= to allow execution at unlock time [OK]

Common Mistakes:

• Using > excludes unlockTime moment
• Removing require loses protection
• Using block.number causes wrong timing

5.

You want to create a timelock contract that allows an admin to schedule a withdrawal only after 1 day from scheduling. Which approach correctly implements this?

contract Timelock {
  address public admin;
  uint256 public unlockTime;

  constructor() {
    admin = msg.sender;
  }

  function scheduleWithdrawal() public {
    require(msg.sender == admin, "Not admin");
    unlockTime = block.timestamp + 86400; // 1 day
  }

  function withdraw() public {
    require(msg.sender == admin, "Not admin");
    require(block.timestamp >= unlockTime, "Too early");
    // withdrawal logic
  }
}

hard

A. Admin cannot schedule withdrawal

B. Withdrawal can happen immediately after scheduling

C. Correctly enforces 1-day delay before withdrawal

D. unlockTime is set incorrectly causing errors

Solution

1. Step 1: Check scheduling sets unlockTime correctly

   The scheduleWithdrawal function sets unlockTime to current time plus 86400 seconds (1 day).

2. Step 2: Verify withdraw enforces timelock

   The withdraw function requires current time to be at or after unlockTime, enforcing the delay.

3. Final Answer:

   Correctly enforces 1-day delay before withdrawal -> Option C

4. Quick Check:

   UnlockTime = now + 1 day, withdraw requires >= unlockTime [OK]

Hint: Add 86400 seconds and check block.timestamp >= unlockTime [OK]

Common Mistakes:

• Not adding delay in schedule function
• Using > instead of >= in withdraw
• Not restricting functions to admin