Sidechains in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a sidechain name.

Blockchain / Solidity

sidechain_name = "[1]"

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

Amainchain

Bblockchain

Csidechain1

Dtokenchain

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'mainchain' instead of a sidechain name

Using generic terms like 'blockchain' that don't specify sidechain

The variable sidechain_name should be set to a valid sidechain identifier, such as "sidechain1".

2fill in blank

medium

Complete the code to initialize the sidechain block height.

Blockchain / Solidity

sidechain_block_height = [1]

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

A"0"

B0

CNone

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string '0' instead of integer 0

Using None or negative numbers

The block height should be an integer starting at 0 for a new sidechain.

3fill in blank

hard

Fix the error in the function that checks if a block belongs to the sidechain.

Blockchain / Solidity

def is_sidechain_block(block):
    return block.chain_id == [1]

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

Asidechain_id

B"sidechain"

C"mainchain"

Dblock.chain_id

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing to a string literal instead of the sidechain ID variable

Comparing the variable to itself

The function should compare block.chain_id to the variable sidechain_id that stores the sidechain's ID.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps block hashes to their heights only for sidechain blocks.

Blockchain / Solidity

sidechain_blocks = {block.hash: block.[1] for block in blocks if block.chain_id [2] sidechain_id}

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

Aheight

B!=

C==

Dindex

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' in the condition

Using 'index' instead of 'height' for block attribute

The dictionary maps each block's hash to its height only if the block's chain_id equals the sidechain_id.

5fill in blank

hard

Fill all three blanks to create a function that returns a list of sidechain block hashes with height greater than a given value.

Blockchain / Solidity

def get_sidechain_hashes(min_height):
    return [block.[1] for block in blocks if block.chain_id == [2] and block.[3] > min_height]

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

Ahash

Bsidechain_id

Cheight

Dtimestamp

Attempts:

3 left

💡 Hint

Common Mistakes

Using timestamp instead of height for comparison

Comparing to wrong chain ID variable

The function returns hashes of blocks where the chain ID matches the sidechain and the block height is greater than min_height.

Practice

1.

What is the main purpose of a sidechain in blockchain technology?

easy

A. To store user passwords securely

B. To replace the main blockchain entirely

C. To mine new cryptocurrencies faster

D. To allow assets to move between blockchains without changing the main chain

Solution

1. Step 1: Understand sidechain function

   Sidechains connect to a main blockchain to move assets safely without altering the main chain.

2. Step 2: Compare options

   Only To allow assets to move between blockchains without changing the main chain describes this purpose correctly; others describe unrelated functions.

3. Final Answer:

   To allow assets to move between blockchains without changing the main chain -> Option D

4. Quick Check:

   Sidechains move assets safely = C [OK]

Hint: Sidechains move assets without changing main chain [OK]

Common Mistakes:

• Thinking sidechains replace main blockchain
• Confusing sidechains with password storage
• Assuming sidechains speed up mining

2.

Which of the following is the correct way to describe the process of moving assets from the main chain to a sidechain?

lockOnMainChain() and issueOnSidechain() are functions.

easy

A. issueOnSidechain(); lockOnMainChain();

B. lockOnMainChain(); issueOnSidechain();

C. burnOnMainChain(); issueOnSidechain();

D. issueOnSidechain(); burnOnMainChain();

Solution

1. Step 1: Understand asset transfer steps

   Assets are locked on the main chain first, then issued on the sidechain.

2. Step 2: Match function order

   lockOnMainChain(); issueOnSidechain(); correctly calls lockOnMainChain() before issueOnSidechain().

3. Final Answer:

   lockOnMainChain(); issueOnSidechain(); -> Option B

4. Quick Check:

   Lock then issue = A [OK]

Hint: Lock assets first, then issue on sidechain [OK]

Common Mistakes:

• Issuing before locking assets
• Using burn instead of lock for main chain
• Mixing function order

3.

Consider this pseudocode for moving assets from a sidechain back to the main chain:

burnOnSidechain()
unlockOnMainChain()

What will be the output if burnOnSidechain() fails?

medium

A. Assets remain locked on the main chain

B. Assets are unlocked on the main chain anyway

C. Assets are burned on the main chain

D. Assets are duplicated on both chains

Solution

1. Step 1: Analyze burn failure effect

   If burnOnSidechain() fails, assets are not removed from the sidechain.

2. Step 2: Understand unlock condition

   unlockOnMainChain() should only run after successful burn; if burn fails, unlock does not happen.

3. Final Answer:

   Assets remain locked on the main chain -> Option A

4. Quick Check:

   Burn must succeed before unlock = D [OK]

Hint: Burn sidechain assets before unlocking main chain [OK]

Common Mistakes:

• Assuming unlock happens even if burn fails
• Thinking assets get duplicated
• Confusing burn with lock

4.

Find the error in this pseudocode for transferring assets to a sidechain:

lockOnMainChain()
issueOnSidechain()
unlockOnMainChain()

medium

A. Unlocking main chain assets immediately after issuing is incorrect

B. Locking assets should happen after issuing

C. Issuing on sidechain should be replaced with burning

D. Unlocking main chain assets is required here

Solution

1. Step 1: Review transfer steps

   Assets must stay locked on the main chain until they are returned from the sidechain.

2. Step 2: Identify incorrect unlock

   Unlocking immediately after issuing breaks asset security; unlock should happen only when assets return.

3. Final Answer:

   Unlocking main chain assets immediately after issuing is incorrect -> Option A

4. Quick Check:

   Unlock only after return = A [OK]

Hint: Don't unlock main chain assets too early [OK]

Common Mistakes:

• Unlocking main chain assets too soon
• Confusing issue with burn
• Reversing lock and issue order

5.

You want to design a sidechain system that allows fast transactions but ensures no asset duplication. Which approach best achieves this?

Choose the correct sequence of actions when moving assets from main chain to sidechain and back.

hard

A. Issue on sidechain -> Lock on main chain -> Unlock on main chain -> Burn on sidechain

B. Burn on main chain -> Issue on sidechain -> Lock on sidechain -> Unlock on main chain

C. Lock on main chain -> Issue on sidechain -> Burn on sidechain -> Unlock on main chain

D. Unlock on main chain -> Burn on sidechain -> Lock on main chain -> Issue on sidechain

Solution

1. Step 1: Understand asset safety steps

   To avoid duplication, assets must be locked on the main chain before issuing on sidechain, and burned on sidechain before unlocking main chain.

2. Step 2: Match correct sequence

   Lock on main chain -> Issue on sidechain -> Burn on sidechain -> Unlock on main chain follows the correct order: lock -> issue -> burn -> unlock, ensuring assets exist only in one place at a time.

3. Final Answer:

   Lock on main chain -> Issue on sidechain -> Burn on sidechain -> Unlock on main chain -> Option C

4. Quick Check:

   Lock, issue, burn, unlock = B [OK]

Hint: Lock before issue; burn before unlock to avoid duplicates [OK]

Common Mistakes:

• Issuing before locking assets
• Unlocking main chain too early
• Burning assets on wrong chain