Sidechains in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Sidechains

User locks coins on Mainchain

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Mainchain records lock

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Sidechain verifies lock proof

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Sidechain issues equivalent coins

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User transacts on Sidechain

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User requests withdrawal

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Sidechain burns coins

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Sidechain provides proof of burn

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Mainchain verifies burn proof

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Mainchain releases locked coins back to user

Sidechains let users move coins from the main blockchain to a separate chain and back by locking and unlocking coins with proofs.

Execution Sample

Blockchain / Solidity

lockCoinsOnMainchain(user, amount)
verifyLockOnSidechain(lockProof)
issueCoinsOnSidechain(user, amount)
burnCoinsOnSidechain(user, amount)
verifyBurnOnMainchain(burnProof)
unlockCoinsOnMainchain(user, amount)

This code shows the main steps to move coins between mainchain and sidechain using lock, verify, issue, burn, verify, and unlock.

Execution Table

Step	Action	Input	State Change	Output/Result
1	lockCoinsOnMainchain	user=Alice, amount=10	Mainchain locks 10 coins from Alice	lockProof generated
2	verifyLockOnSidechain	lockProof	Sidechain confirms lock is valid	lockProof verified
3	issueCoinsOnSidechain	user=Alice, amount=10	Sidechain credits 10 coins to Alice	Alice balance on sidechain = 10
4	User transacts on Sidechain	Alice sends 5 coins to Bob	Alice balance=5, Bob balance=5	Transaction success
5	burnCoinsOnSidechain	user=Alice, amount=5	Sidechain burns 5 coins from Alice	burnProof generated
6	verifyBurnOnMainchain	burnProof	Mainchain confirms burn is valid	burnProof verified
7	unlockCoinsOnMainchain	user=Alice, amount=5	Mainchain releases 5 coins back to Alice	Alice balance on mainchain increased by 5
8	End	N/A	No further actions	Process complete

💡 Process stops after coins are unlocked back on mainchain to user

Variable Tracker

Variable	Start	After Step 3	After Step 4	After Step 5	After Step 7	Final
Alice_mainchain_balance	100	90 (locked 10)	90	90	95 (unlocked 5)	95
Alice_sidechain_balance	0	10 (issued)	5 (sent 5 to Bob)	0 (burned 5)	0	0
Bob_sidechain_balance	0	0	5 (received 5)	5	5	5

Key Moments - 3 Insights

Why does Alice's mainchain balance decrease before she can use coins on the sidechain?

Because coins are locked on the mainchain first (see Step 1 and variable 'Alice_mainchain_balance' after Step 3), so they can't be spent there until unlocked.

How does the sidechain know it can safely issue coins to Alice?

It verifies the lock proof from the mainchain (Step 2), ensuring coins are locked and not double-spent.

Why must coins be burned on the sidechain before unlocking on the mainchain?

Burning coins on the sidechain (Step 5) prevents double spending by destroying sidechain coins before mainchain coins are released (Step 7).

Visual Quiz - 3 Questions

Look at the execution table, what is Alice's sidechain balance after Step 4?

A 10

B 5

C 0

D 15

💡 Hint

Check the 'State Change' column at Step 4 showing Alice sends 5 coins to Bob.

At which step does the mainchain release coins back to Alice?

A Step 5

B Step 6

C Step 7

D Step 3

💡 Hint

Look for 'unlockCoinsOnMainchain' action in the execution table.

If Alice did not burn coins on the sidechain, what would happen in the process?

A Mainchain would not verify burn proof and not unlock coins

B Sidechain would issue more coins

C Mainchain would still unlock coins

D Alice's mainchain balance would increase

💡 Hint

Refer to Step 6 where mainchain verifies burn proof before unlocking coins.

Concept Snapshot

Sidechains let users move coins between blockchains.
Coins are locked on mainchain, then issued on sidechain.
Users transact on sidechain freely.
To return coins, sidechain coins are burned.
Mainchain verifies burn proof and unlocks coins.
This prevents double spending across chains.

Full Transcript

Sidechains are a way to move coins from a main blockchain to a separate blockchain and back. The process starts when a user locks coins on the mainchain, which means those coins cannot be spent there anymore. The mainchain creates a proof of this lock. The sidechain checks this proof and then issues the same amount of coins to the user on the sidechain. The user can then use these coins on the sidechain, for example sending some to another user. When the user wants to move coins back, they burn coins on the sidechain, destroying them. The sidechain creates a proof of this burn. The mainchain verifies this burn proof and then unlocks the original coins back to the user. This process ensures coins are never spent twice and keeps both chains in sync.