Public vs private blockchains - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Which statement best describes a public blockchain?

Choose the statement that correctly describes a public blockchain.

A It is controlled by a single organization with restricted access.

B Anyone can join and participate without permission.

C Only invited members can join and validate transactions.

D It uses a private network with no public access.

💡 Hint

Think about who can access and participate in a public blockchain.

A public blockchain is open to everyone. Anyone can join, validate transactions, and participate without needing permission.

🧠 Conceptual

intermediate

What is a key feature of a private blockchain?

Identify the key feature that distinguishes a private blockchain from a public one.

A It is maintained by a decentralized group of unknown validators.

B It allows anonymous participation from anyone worldwide.

C It uses proof-of-work mining to secure the network.

D It restricts access to a selected group of participants.

💡 Hint

Consider who controls access in a private blockchain.

Private blockchains restrict access to a specific group, usually controlled by an organization or consortium.

❓ Predict Output

advanced

What is the output of this blockchain node access check?

Given the code below simulating node access in a blockchain network, what will be printed?

Blockchain / Solidity

class BlockchainNode:
    def __init__(self, is_public):
        self.is_public = is_public
    def can_join(self, user):
        if self.is_public:
            return True
        else:
            return user in ['Alice', 'Bob']

node_public = BlockchainNode(True)
node_private = BlockchainNode(False)

print(node_public.can_join('Eve'))
print(node_private.can_join('Eve'))

A True\nTrue

B False\nTrue

C True\nFalse

D False\nFalse

💡 Hint

Check how the can_join method works for public and private nodes.

The public node allows anyone to join, so 'Eve' returns True. The private node only allows 'Alice' and 'Bob', so 'Eve' returns False.

❓ Predict Output

advanced

What error does this private blockchain access code raise?

Analyze the code below and identify the error it produces when run.

Blockchain / Solidity

class PrivateBlockchain:
    def __init__(self, members):
        self.members = members
    def add_member(self, member):
        if member not in self.members:
            self.members.append(member)
    def validate_transaction(self, user):
        if user not in self.members:
            raise PermissionError('User not authorized')
        return 'Transaction validated'

chain = PrivateBlockchain(['Alice', 'Bob'])
print(chain.validate_transaction('Eve'))

A PermissionError: User not authorized

B AttributeError: 'PrivateBlockchain' object has no attribute 'members'

C TypeError: 'in' requires string as left operand

D No error, prints 'Transaction validated'

💡 Hint

Look at the validate_transaction method and the user passed.

The user 'Eve' is not in the members list, so the method raises a PermissionError with the message 'User not authorized'.

🧠 Conceptual

expert

Which blockchain type best fits a company needing fast, private transactions with controlled access?

Choose the blockchain type that best suits a company requiring fast transaction processing, privacy, and controlled participant access.

A Private blockchain with restricted access and permissioned nodes.

B Public blockchain with open participation and proof-of-work consensus.

C Public blockchain with anonymous nodes and no access control.

D Hybrid blockchain with no restrictions on transaction visibility.

💡 Hint

Consider privacy and access control needs for a company.

A private blockchain with permissioned nodes offers controlled access and privacy, making it suitable for companies needing fast and private transactions.