Briefly discuss the concept of EVM and Ethereum gas and structure of transaction in ethereum?

Ethereum Virtual Machine (EVM):

The Ethereum Virtual Machine (EVM) is the runtime environment for smart contracts in Ethereum. It is completely isolated from the main Ethereum network, which makes it a perfect sandbox for testing smart contracts. The EVM is Turing complete, meaning it can run scripts of any complexity given enough time and memory.

Ethereum Gas:

Gas in Ethereum is the measure of computational effort required to execute specific operations. Each operation has a fixed amount of gas associated with it. Gas is used to allocate resources of the EVM so that decentralized apps running on the network don't consume more resources than they need to. When you send a transaction, you specify a gas limit and a gas price. The gas limit is the maximum amount of gas you're willing to use, and the gas price is the amount of ETH you're willing to spend per unit of gas.

Structure of Transaction in Ethereum:

A transaction in Ethereum contains the following fields:

1. Nonce: A value that can only be used once. This is used to prevent the same transaction from being processed more than once.

2. GasPrice: The price you are willing to pay per gas unit.

3. GasLimit: The maximum amount of gas units that can be used for this transaction.

4. To: The address of the recipient.

5. Value: The amount of Ether to send.

6. Data: The input data for the transaction. This could be the contract method and parameters, in case of a contract call, or the initialization code, in case of contract creation.

7. v, r, s: These values are used to generate the signature of the transaction and to recover the sender's address from the signature.