Public vs private blockchains - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a public blockchain property.

Blockchain / Solidity

blockchain_type = '[1]'

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

Aprivate

Bcentralized

Cpublic

Dpermissioned

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'private' or 'permissioned' which restrict access.

The code sets the blockchain type to 'public', which means anyone can join and participate.

2fill in blank

medium

Complete the code to check if a blockchain is private.

Blockchain / Solidity

if blockchain_type == '[1]':
    access = 'restricted'

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

Aprivate

Bpublic

Copen

Ddecentralized

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'public' which means open access.

The condition checks if the blockchain is 'private', which means access is restricted.

3fill in blank

hard

Fix the error in the code to correctly identify a public blockchain.

Blockchain / Solidity

def is_public(chain):
    return chain == '[1]'

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

Aprivate

Bclosed

Cpermissioned

Dpublic

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for 'private' or 'permissioned' which are restricted.

The function returns True if the chain is 'public', meaning open to all.

4fill in blank

hard

Fill both blanks to create a dictionary showing blockchain types and their access.

Blockchain / Solidity

blockchain_access = {
    'public': '[1]',
    'private': '[2]'
}

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

Aopen

Brestricted

Cclosed

Dpermissioned

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up 'open' and 'restricted' values.

Public blockchains have 'open' access, private blockchains have 'restricted' access.

5fill in blank

hard

Fill all three blanks to complete the function that returns blockchain access type.

Blockchain / Solidity

def get_access_type(blockchain):
    if blockchain == '[1]':
        return '[2]'
    else:
        return '[3]'

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

Apublic

Bopen

Crestricted

Dprivate

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping access types or blockchain names.

The function returns 'open' for public blockchains and 'restricted' for others (private).

Practice

1. Which statement best describes a public blockchain?

easy

A. Anyone can join and participate without permission.

B. Only invited members can access the network.

C. It is controlled by a single organization.

D. It uses private keys only for administrators.

Solution

1. Step 1: Understand public blockchain access

   Public blockchains are open networks where anyone can join and participate without needing permission.

2. Step 2: Compare with private blockchain features

   Private blockchains restrict access to trusted members, unlike public ones.

3. Final Answer:

   Anyone can join and participate without permission. -> Option A

4. Quick Check:

   Public blockchain = open access [OK]

Hint: Public means open to all, no permission needed [OK]

Common Mistakes:

• Confusing public with private blockchain access
• Thinking public blockchains are controlled by one entity
• Assuming private keys limit public blockchain access

2. Which of the following is the correct way to describe a private blockchain?

easy

A. It is always slower than public blockchains.

B. It allows anyone to validate transactions.

C. It restricts access to selected participants only.

D. It uses proof-of-work exclusively.

Solution

1. Step 1: Identify private blockchain access rules

   Private blockchains restrict access to selected participants, unlike public blockchains.

2. Step 2: Eliminate incorrect options

   Private blockchains do not necessarily use proof-of-work or are always slower; these are unrelated to access control.

3. Final Answer:

   It restricts access to selected participants only. -> Option C

4. Quick Check:

   Private blockchain = restricted access [OK]

Hint: Private means limited access to trusted members only [OK]

Common Mistakes:

• Assuming private blockchains allow anyone to validate
• Confusing consensus methods with access control
• Believing private blockchains are always slower

3. Consider this code snippet representing blockchain access control:

def can_access(user, blockchain_type):
    if blockchain_type == 'public':
        return True
    elif blockchain_type == 'private':
        return user in ['Alice', 'Bob']
    else:
        return False

print(can_access('Alice', 'public'))
print(can_access('Eve', 'private'))
print(can_access('Bob', 'private'))

What is the output?

medium

A. False
False
True

B. True
False
True

C. True
True
False

D. False
True
False

Solution

1. Step 1: Evaluate access for 'Alice' on public blockchain

   Public blockchain always returns True, so can_access('Alice', 'public') is True.

2. Step 2: Evaluate access for 'Eve' on private blockchain

   'Eve' is not in ['Alice', 'Bob'], so can_access('Eve', 'private') returns False.

3. Step 3: Evaluate access for 'Bob' on private blockchain

   'Bob' is in the allowed list, so can_access('Bob', 'private') returns True.

4. Final Answer:

   True False True -> Option B

5. Quick Check:

   Public always True, private checks user list [OK]

Hint: Public always True; private checks user list membership [OK]

Common Mistakes:

• Assuming private blockchain allows all users
• Mixing up True/False return values
• Ignoring the user list check for private blockchains

4. The following code is intended to check if a user can access a private blockchain. What is the error?

def check_access(user, blockchain):
    if blockchain == 'private':
        if user == ['Alice', 'Bob']:
            return True
        else:
            return False
    else:
        return True

print(check_access('Alice', 'private'))

medium

A. The user comparison uses == with a list instead of membership check.

B. The function does not return anything for public blockchains.

C. The else block is missing for private blockchain condition.

D. The print statement has incorrect syntax.

Solution

1. Step 1: Analyze user comparison in private blockchain check

   The code uses 'user == ['Alice', 'Bob']' which compares a string to a list, always False.

2. Step 2: Identify correct way to check user membership

   It should use 'user in ['Alice', 'Bob']' to check if user is in the allowed list.

3. Final Answer:

   The user comparison uses == with a list instead of membership check. -> Option A

4. Quick Check:

   Use 'in' to check list membership, not '==' [OK]

Hint: Use 'in' to check if user is in list, not '==' [OK]

Common Mistakes:

• Using '==' to compare a string with a list
• Forgetting to handle public blockchain case
• Syntax errors in print statement

5. You want to design a blockchain system for a company where only employees can add transactions, but anyone can view the ledger. Which blockchain type fits best and why?

hard

A. Private blockchain, because it hides the ledger from everyone except employees.

B. Public blockchain, because it allows everyone to add transactions.

C. Public blockchain, because it restricts access to employees only.

D. Private blockchain, because it restricts who can add transactions but allows public viewing.

Solution

1. Step 1: Identify who can add transactions

   The company wants only employees to add transactions, so write access must be restricted.

2. Step 2: Identify who can view the ledger

   Anyone can view the ledger, so read access is open to the public.

3. Step 3: Match blockchain type to requirements

   Private blockchains restrict write access to trusted members but can allow public read access, fitting the need.

4. Final Answer:

   Private blockchain, because it restricts who can add transactions but allows public viewing. -> Option D

5. Quick Check:

   Restrict writes, allow public reads = Private blockchain [OK]

Hint: Restrict who writes, allow public reads means private blockchain [OK]

Common Mistakes:

• Choosing public blockchain for restricted write access
• Thinking private blockchain hides ledger from public
• Confusing read and write permissions