Public vs private blockchains - Visual Side-by-Side Comparison

Concept Flow - Public vs private blockchains

Start

↓

Choose Blockchain Type

↓

Public Blockchain

↓

Open to Everyone

↓

Decentralized

↓

Consensus by All

↓

Transparent

↓

End

This flow shows the choice between public and private blockchains, highlighting their access, control, consensus, and transparency differences.

Execution Sample

Blockchain / Solidity

blockchain_type = 'public'
if blockchain_type == 'public':
    access = 'open to everyone'
else:
    access = 'restricted access'
print(access)

This code checks the blockchain type and sets access accordingly, then prints the access type.

Execution Table

Step	blockchain_type	Condition	Branch Taken	access	Output
1	'public'	blockchain_type == 'public'	True	open to everyone
2	'public'	else	False		open to everyone

💡 Condition true at Step 1 (if branch taken), else skipped (Step 2), access set and printed, execution ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
blockchain_type	'public'	'public'	'public'	'public'
access	undefined	'open to everyone'	'open to everyone'	'open to everyone'

Key Moments - 2 Insights

Why does the code choose 'open to everyone' access?

Because the variable blockchain_type is 'public', the condition blockchain_type == 'public' is True at Step 1 in the execution_table, so the code sets access to 'open to everyone'.

What happens if blockchain_type is not 'public'?

The condition at Step 1 becomes False, so the else branch runs (Step 2), setting access to 'restricted access' instead.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'access' after Step 1?

A 'open to everyone'

B 'restricted access'

C undefined

D 'public'

💡 Hint

Check the 'access' column in the row for Step 1 in execution_table.

At which step does the else branch run if blockchain_type is 'private'?

A Step 1

B Step 2

C No step, code stops

D Step 3

💡 Hint

Look at the 'Branch Taken' column for the else condition in execution_table.

If blockchain_type changes to 'private', how does the 'access' variable change in variable_tracker?

A It stays 'open to everyone'

B It becomes undefined

C It becomes 'restricted access'

D It becomes 'public'

💡 Hint

Refer to the explanation in key_moments about the else branch and variable_tracker changes.

Concept Snapshot

Public vs Private Blockchains:
- Public: open to everyone, decentralized, consensus by all, transparent.
- Private: restricted access, centralized control, consensus by selected nodes, limited transparency.
- Access control is key difference.
- Code example shows simple access assignment based on type.

Full Transcript

This visual execution compares public and private blockchains by showing a simple code example that sets access based on blockchain type. The flow diagram outlines the decision path from choosing blockchain type to access and consensus differences. The execution table traces the code steps, showing how the condition blockchain_type == 'public' leads to setting access to 'open to everyone'. The variable tracker follows variable changes step by step. Key moments clarify why the code chooses one branch over another. The quiz tests understanding of variable values and branching decisions. The snapshot summarizes the main differences and the code logic.

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