Access control with OpenZeppelin in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the AccessControl contract from OpenZeppelin.

Blockchain / Solidity

import "@openzeppelin/contracts/access/[1].sol";

Drag options to blanks, or click blank then click option'

AAccessControl

BERC20

CPausable

DOwnable

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Ownable instead of AccessControl.

Using ERC20 which is for tokens.

Forgetting the .sol extension.

The AccessControl contract is imported from OpenZeppelin to manage roles and permissions.

2fill in blank

medium

Complete the code to declare a role identifier for ADMIN_ROLE.

Blockchain / Solidity

bytes32 public constant ADMIN_ROLE = [1]("ADMIN_ROLE");

Drag options to blanks, or click blank then click option'

Ahash256

Bsha256

Ckeccak256

DencodePacked

Attempts:

3 left

💡 Hint

Common Mistakes

Using sha256 which is different from keccak256.

Using hash256 which does not exist.

Using encodePacked which returns bytes, not bytes32.

keccak256 is used to create a unique bytes32 identifier for roles.

3fill in blank

hard

Fix the error in the constructor to grant ADMIN_ROLE to the deployer.

Blockchain / Solidity

constructor() {
    _setupRole([1], msg.sender);
}

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ADEFAULT_ADMIN_ROLE

BADMIN_ROLE

COWNER_ROLE

DMINTER_ROLE

Attempts:

3 left

💡 Hint

Common Mistakes

Using DEFAULT_ADMIN_ROLE which is different.

Using OWNER_ROLE which is not declared.

Using MINTER_ROLE which is unrelated.

The ADMIN_ROLE constant should be granted to the deployer in the constructor.

4fill in blank

hard

Fill both blanks to restrict the function to only ADMIN_ROLE holders.

Blockchain / Solidity

function restrictedAction() public [1](ADMIN_ROLE) [2] {
    // action code
}

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AonlyRole

Bpublic

Cexternal

Dview

Attempts:

3 left

💡 Hint

Common Mistakes

Using external visibility which is valid but not the intended answer here.

Using view which restricts state changes.

Omitting the onlyRole modifier.

The onlyRole modifier restricts access, and the function visibility is public.

5fill in blank

hard

Fill all three blanks to create a new role and grant it to an address.

Blockchain / Solidity

bytes32 public constant [1] = keccak256("[1]_ROLE");

function grantNewRole(address user) public [2](ADMIN_ROLE) {
    _grantRole([1], user);
}

Drag options to blanks, or click blank then click option'

AMINTER

BonlyRole

DPAUSER

Attempts:

3 left

💡 Hint

Common Mistakes

Using PAUSER instead of MINTER.

Omitting the onlyRole modifier.

Mismatching role names.

The MINTER role is declared and granted using onlyRole modifier to restrict access.

Practice

1. What is the main purpose of using onlyRole modifier in OpenZeppelin's Access Control?

easy

A. To restrict function access to accounts with a specific role

B. To automatically assign roles to all users

C. To allow anyone to call the function without restrictions

D. To log all function calls for auditing

Solution

1. Step 1: Understand the purpose of onlyRole

   The onlyRole modifier is used to limit access to functions so only users with a certain role can execute them.

2. Step 2: Analyze the options

   To restrict function access to accounts with a specific role correctly states that it restricts function access to accounts with a specific role. Other options describe unrelated behaviors.

3. Final Answer:

   To restrict function access to accounts with a specific role -> Option A

4. Quick Check:

   Access control = restrict by role [OK]

Hint: Remember: onlyRole means only users with that role can call [OK]

Common Mistakes:

• Thinking onlyRole assigns roles automatically
• Believing onlyRole allows open access
• Confusing onlyRole with event logging

2. Which of the following is the correct way to declare a role constant in OpenZeppelin Access Control?

easy

A. address constant ADMIN_ROLE = 0x123;

B. string public ADMIN_ROLE = "ADMIN_ROLE";

C. uint256 constant ADMIN_ROLE = 1;

D. bytes32 public constant ADMIN_ROLE = keccak256("ADMIN_ROLE");

Solution

1. Step 1: Recall role declaration syntax

   OpenZeppelin uses bytes32 constants with keccak256 hash of a string to define roles.

2. Step 2: Check each option

   bytes32 public constant ADMIN_ROLE = keccak256("ADMIN_ROLE"); matches the correct pattern. Options B, C, and D use wrong types or formats.

3. Final Answer:

   bytes32 public constant ADMIN_ROLE = keccak256("ADMIN_ROLE"); -> Option D

4. Quick Check:

   Role constants use bytes32 + keccak256 [OK]

Hint: Roles are bytes32 constants hashed with keccak256 [OK]

Common Mistakes:

• Using string instead of bytes32 for roles
• Assigning numeric or address types to roles
• Forgetting to use keccak256 hash

3. Given the following Solidity code snippet, what will happen if an account without the ADMIN_ROLE calls secureFunction()?

contract MyContract is AccessControl {
    bytes32 public constant ADMIN_ROLE = keccak256("ADMIN_ROLE");

    constructor() {
        _grantRole(ADMIN_ROLE, msg.sender);
    }

    function secureFunction() public onlyRole(ADMIN_ROLE) {
        // critical logic
    }
}

medium

A. The function executes normally

B. The call reverts with an access control error

C. The function executes but emits a warning

D. The function executes only if the caller is the contract owner

Solution

1. Step 1: Understand the onlyRole modifier behavior

   The onlyRole(ADMIN_ROLE) modifier restricts access to accounts with ADMIN_ROLE. If the caller lacks this role, the call reverts.

2. Step 2: Analyze the scenario

   The constructor grants ADMIN_ROLE only to msg.sender at deployment. Any other account calling secureFunction will trigger a revert due to missing role.

3. Final Answer:

   The call reverts with an access control error -> Option B

4. Quick Check:

   Missing role causes revert [OK]

Hint: Only accounts with role can call; others revert [OK]

Common Mistakes:

• Assuming function runs without role
• Thinking warnings are emitted instead of revert
• Confusing role with ownership

4. Identify the error in this OpenZeppelin Access Control code snippet:

contract MyContract is AccessControl {
    bytes32 public constant ADMIN_ROLE = keccak256("ADMIN_ROLE");

    constructor() {
        _grantRole(ADMIN_ROLE, msg.sender);
    }

    function restricted() public onlyRole(ADMIN_ROLE) {
        // restricted logic
    }

    function grantAdmin(address user) public {
        _grantRole(ADMIN_ROLE, user);
    }
}

medium

A. The grantAdmin function lacks access control and can be called by anyone

B. The _setupRole function is deprecated and should not be used

C. The onlyRole modifier is missing from grantAdmin

D. The ADMIN_ROLE constant is incorrectly declared

Solution

1. Step 1: Review access control on grantAdmin

   The grantAdmin function calls _grantRole but has no modifier restricting who can call it.

2. Step 2: Identify security risk

   Without access control, anyone can call grantAdmin and assign ADMIN_ROLE to themselves or others, breaking security.

3. Final Answer:

   The grantAdmin function lacks access control and can be called by anyone -> Option A

4. Quick Check:

   Grant functions need access control [OK]

Hint: Always protect grantRole functions with onlyRole [OK]

Common Mistakes:

• Ignoring missing access control on grant functions
• Thinking _grantRole is protected like grantRole
• Confusing role declaration syntax

5. You want to create a smart contract where only users with the MINTER_ROLE can mint tokens, and only the contract owner can assign the MINTER_ROLE. Which OpenZeppelin pattern correctly enforces this?

hard

A. Use Ownable and allow only the owner to mint tokens directly without roles

B. Use AccessControl but allow anyone to assign MINTER_ROLE to themselves

C. Use AccessControl with MINTER_ROLE and add onlyRole(DEFAULT_ADMIN_ROLE) modifier to the role assignment function, granting DEFAULT_ADMIN_ROLE to the owner

D. Use AccessControl and assign MINTER_ROLE to everyone by default

Solution

1. Step 1: Understand role assignment control

   To restrict who can assign MINTER_ROLE, use AccessControl's DEFAULT_ADMIN_ROLE for admin rights and protect assignment functions with onlyRole(DEFAULT_ADMIN_ROLE).

2. Step 2: Connect owner with DEFAULT_ADMIN_ROLE

   Grant DEFAULT_ADMIN_ROLE to the contract owner so only they can assign MINTER_ROLE to others.

3. Final Answer:

   Use AccessControl with MINTER_ROLE and add onlyRole(DEFAULT_ADMIN_ROLE) modifier to the role assignment function, granting DEFAULT_ADMIN_ROLE to the owner -> Option C

4. Quick Check:

   Admin role controls role assignment [OK]

Hint: Use DEFAULT_ADMIN_ROLE for owner to control role assignments [OK]

Common Mistakes:

• Allowing anyone to assign roles
• Using Ownable without roles for minting
• Assigning roles to everyone by default