Transactions
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Transactions are cryptographically signed instructions from accounts. An account will initiate a transaction to update the state of the Ethereum network. The simplest transaction is transferring ETH from one account to another.
Prerequisites
To help you better understand this page, we recommend you first read Accounts and our introduction to Ethereum.
What's a transaction?
An Ethereum transaction refers to an action initiated by an externally-owned account, in other words an account managed by a human, not a contract. For example, if Bob sends Alice 1 ETH, Bob's account must be debited and Alice's must be credited. This state-changing action takes place within a transaction.
Diagram adapted from Ethereum EVM illustrated(opens in a new tab)
Transactions, which change the state of the EVM, need to be broadcast to the whole network. Any node can broadcast a request for a transaction to be executed on the EVM; after this happens, a validator will execute the transaction and propagate the resulting state change to the rest of the network.
Transactions require a fee and must be included in a validated block. To make this overview simpler we'll cover gas fees and validation elsewhere.
A submitted transaction includes the following information:
from
– the address of the sender, that will be signing the transaction. This will be an externally-owned account as contract accounts cannot send transactions.to
– the receiving address (if an externally-owned account, the transaction will transfer value. If a contract account, the transaction will execute the contract code)signature
– the identifier of the sender. This is generated when the sender's private key signs the transaction and confirms the sender has authorized this transactionnonce
- a sequentially incrementing counter which indicates the transaction number from the accountvalue
– amount of ETH to transfer from sender to recipient (denominated in WEI, where 1ETH equals 1e+18wei)input data
– optional field to include arbitrary datagasLimit
– the maximum amount of gas units that can be consumed by the transaction. The EVM specifies the units of gas required by each computational stepmaxPriorityFeePerGas
- the maximum price of the consumed gas to be included as a tip to the validatormaxFeePerGas
- the maximum fee per unit of gas willing to be paid for the transaction (inclusive ofbaseFeePerGas
andmaxPriorityFeePerGas
)
Gas is a reference to the computation required to process the transaction by a validator. Users have to pay a fee for this computation. The gasLimit
, and maxPriorityFeePerGas
determine the maximum transaction fee paid to the validator. More on Gas.
The transaction object will look a little like this:
1{2 from: "0xEA674fdDe714fd979de3EdF0F56AA9716B898ec8",3 to: "0xac03bb73b6a9e108530aff4df5077c2b3d481e5a",4 gasLimit: "21000",5 maxFeePerGas: "300",6 maxPriorityFeePerGas: "10",7 nonce: "0",8 value: "10000000000"9}إظهار الكلنسخ
But a transaction object needs to be signed using the sender's private key. This proves that the transaction could only have come from the sender and was not sent fraudulently.
An Ethereum client like Geth will handle this signing process.
Example JSON-RPC call:
1{2 "id": 2,3 "jsonrpc": "2.0",4 "method": "account_signTransaction",5 "params": [6 {7 "from": "0x1923f626bb8dc025849e00f99c25fe2b2f7fb0db",8 "gas": "0x55555",9 "maxFeePerGas": "0x1234",10 "maxPriorityFeePerGas": "0x1234",11 "input": "0xabcd",12 "nonce": "0x0",13 "to": "0x07a565b7ed7d7a678680a4c162885bedbb695fe0",14 "value": "0x1234"15 }16 ]17}إظهار الكلنسخ
Example response:
1{2 "jsonrpc": "2.0",3 "id": 2,4 "result": {5 "raw": "0xf88380018203339407a565b7ed7d7a678680a4c162885bedbb695fe080a44401a6e4000000000000000000000000000000000000000000000000000000000000001226a0223a7c9bcf5531c99be5ea7082183816eb20cfe0bbc322e97cc5c7f71ab8b20ea02aadee6b34b45bb15bc42d9c09de4a6754e7000908da72d48cc7704971491663",6 "tx": {7 "nonce": "0x0",8 "maxFeePerGas": "0x1234",9 "maxPriorityFeePerGas": "0x1234",10 "gas": "0x55555",11 "to": "0x07a565b7ed7d7a678680a4c162885bedbb695fe0",12 "value": "0x1234",13 "input": "0xabcd",14 "v": "0x26",15 "r": "0x223a7c9bcf5531c99be5ea7082183816eb20cfe0bbc322e97cc5c7f71ab8b20e",16 "s": "0x2aadee6b34b45bb15bc42d9c09de4a6754e7000908da72d48cc7704971491663",17 "hash": "0xeba2df809e7a612a0a0d444ccfa5c839624bdc00dd29e3340d46df3870f8a30e"18 }19 }20}إظهار الكلنسخ
- the
raw
is the signed transaction in Recursive Length Prefix (RLP) encoded form - the
tx
is the signed transaction in JSON form
With the signature hash, the transaction can be cryptographically proven that it came from the sender and submitted to the network.
The data field
The vast majority of transactions access a contract from an externally-owned account. Most contracts are written in Solidity and interpret their data field in accordance with the .
The first four bytes specify which function to call, using the hash of the function's name and arguments. You can sometimes identify the function from the selector using this database(opens in a new tab).
The rest of the calldata is the arguments, encoded as specified in the ABI specs(opens in a new tab).
For example, lets look at this transaction(opens in a new tab). Use Click to see More to see the calldata.
The function selector is 0xa9059cbb
. There are several known functions with this signature(opens in a new tab).
In this case the contract source code(opens in a new tab) has been uploaded to Etherscan, so we know the function is transfer(address,uint256)
.
The rest of the data is:
10000000000000000000000004f6742badb049791cd9a37ea913f2bac38d012792000000000000000000000000000000000000000000000000000000003b0559f4
According to the ABI specifications, integer values (such as addresses, which are 20-byte integers) appear in the ABI as 32-byte words, padded with zeros in the front.
So we know that the to
address is 4f6742badb049791cd9a37ea913f2bac38d01279
(opens in a new tab).
The value
is 0x3b0559f4 = 990206452.
Types of transactions
On Ethereum there are a few different types of transactions:
- Regular transactions: a transaction from one account to another.
- Contract deployment transactions: a transaction without a 'to' address, where the data field is used for the contract code.
- Execution of a contract: a transaction that interacts with a deployed smart contract. In this case, 'to' address is the smart contract address.
On gas
As mentioned, transactions cost gas to execute. Simple transfer transactions require 21000 units of Gas.
So for Bob to send Alice 1 ETH at a baseFeePerGas
of 190 gwei and maxPriorityFeePerGas
of 10 gwei, Bob will need to pay the following fee:
1(190 + 10) * 21000 = 4,200,000 gwei2--or--30.0042 ETH
Bob's account will be debited -1.0042 ETH (1 ETH for Alice + 0.0042 ETH in gas fees)
Alice's account will be credited +1.0 ETH
The base fee will be burned -0.00399 ETH
Validator keeps the tip +0.000210 ETH
Diagram adapted from Ethereum EVM illustrated(opens in a new tab)
Any gas not used in a transaction is refunded to the user account.
Smart contract interactions
Gas is required for any transaction that involves a smart contract.
Smart contracts can also contain functions known as view
(opens in a new tab) or pure
(opens in a new tab) functions, which do not alter the state of the contract. As such, calling these functions from an EOA will not require any gas. The underlying RPC call for this scenario is eth_call
Unlike when accessed using eth_call
, these view
or pure
functions are also commonly called internally (i.e. from the contract itself or from another contract) which does cost gas.
Transaction lifecycle
Once the transaction has been submitted the following happens:
- A transaction hash is cryptographically generated:
0x97d99bc7729211111a21b12c933c949d4f31684f1d6954ff477d0477538ff017
- The transaction is then broadcasted to the network and added to a transaction pool consisting of all other pending network transactions.
- A validator must pick your transaction and include it in a block in order to verify the transaction and consider it "successful".
- As time passes the block containing your transaction will be upgraded to "justified" then "finalized". These upgrades make it much more certain that your transaction was successful and will never be altered. Once a block is "finalized" it could only ever be changed by a network level attack that would cost many billions of dollars.
A visual demo
Watch Austin walk you through transactions, gas, and mining.
Typed Transaction Envelope
Ethereum originally had one format for transactions. Each transaction contained a nonce, gas price, gas limit, to address, value, data, v, r, and s. These fields are RLP-encoded, to look something like this:
RLP([nonce, gasPrice, gasLimit, to, value, data, v, r, s])
Ethereum has evolved to support multiple types of transactions to allow for new features such as access lists and EIP-1559(opens in a new tab) to be implemented without affecting legacy transaction formats.
EIP-2718(opens in a new tab) is what allows for this behavior. Transactions are interpreted as:
TransactionType || TransactionPayload
Where the fields are defined as:
TransactionType
- a number between 0 and 0x7f, for a total of 128 possible transaction types.TransactionPayload
- an arbitrary byte array defined by the transaction type.
Based on the TransactionType
value, a transaction can be classified as
Type 0 (Legacy) Transactions: The original transaction format used since Ethereum's launch. They do not include features from EIP-1559(opens in a new tab) such as dynamic gas fee calculations or access lists for smart contracts. Legacy transactions lack a specific prefix indicating their type in their serialized form, starting with the byte
0xf8
when using Recursive Length Prefix (RLP) encoding. The TransactionType value for these transactions is0x0
.Type 1 Transactions: Introduced in EIP-2930(opens in a new tab) as part of Ethereum's Berlin Upgrade, these transactions include an
accessList
parameter. This list specifies addresses and storage keys the transaction expects to access, helping to potentially reduce gas costs for complex transactions involving smart contracts. EIP-1559 fee market changes are not included in Type 1 transactions. Type 1 transactions also include ayParity
parameter, which can either be0x0
or0x1
, indicating the parity of the y-value of the secp256k1 signature. They are identified by starting with the byte0x01
, and their TransactionType value is0x1
.Type 2 Transactions, commonly referred to as EIP-1559 transactions, are transactions introduced in EIP-1559(opens in a new tab), in Ethereum's London Upgrade. They have become the standard transaction type on the Ethereum network. These transactions introduce a new fee market mechanism that improves predictability by separating the transaction fee into a base fee and a priority fee. They start with the byte
0x02
and include fields such asmaxPriorityFeePerGas
andmaxFeePerGas
. Type 2 transactions are now the default due to their flexibility and efficiency, especially favored during periods of high network congestion for their ability to help users manage transaction fees more predictably. The TransactionType value for these transactions is0x2
.
Further reading
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