What are Contract Creation Transactions and Message Call Transactions? Explain with a suitable diagram.

In Ethereum, every action that changes the blockchain’s state is initiated through a transaction. There are two primary types of transactions:

1. Contract Creation Transaction – used to deploy a new smart contract on the blockchain.
2. Message Call Transaction – used to invoke an existing contract’s function or to send Ether between accounts.

2. Contract Creation Transaction

A Contract Creation Transaction is triggered when a user wants to deploy a new smart contract.

Required Parameters:

• Sender Address
• Nonce
• Gas & Gas Price
• Value (Endowment in Wei)
• Init Code (EVM code for deployment)

Working:

• The init code is executed once and returns the contract’s runtime code.
• A new contract address is created using:
  Keccak256(sender + nonce) → last 20 bytes → new contract address
• If successful, the runtime code is stored at the new address.
• If an error (like out-of-gas), the contract is not created, and state reverts.

3. Message Call Transaction

A Message Call Transaction is used to:

• Transfer Ether between accounts, or
• Call a function inside an existing smart contract.

Required Parameters:

• Sender and Recipient Address
• Gas & Gas Price
• Value (in Wei)
• Input Data (function selector + parameters)

Working:

• The transaction sends input data to the contract.
• If the contract has code, it gets executed.
• If successful, state changes (e.g., data stored, balances updated).
• It can also return data or trigger internal calls to other contracts.

4. Differences between Contract Creation and Message Call