Working with Local Private Keys

Local vs Hosted Nodes

Hosted Node

A hosted node is controlled by someone else. When you connect to Infura, you are connected to a hosted node. See for the list of free and commercial node providers.

Local Node

A local node is started and controlled by you on your computer. For several reasons (e.g., privacy, security), this is the recommended path, but it requires more resources and work to set up and maintain.

Local vs Hosted Keys

An Ethereum private key is a 256-bit (32 bytes) random integer. For each private key, you get one Ethereum address, also known as an Externally Owned Account (EOA).

In Python, the private key is expressed as a 32-byte long Python bytes object. When a private key is presented to users in a hexadecimal format, it may or may not contain a starting 0x hexadecimal prefix.

Local Private Key

A local private key is a locally stored secret you import to your Python application. Please read below how you can create and import a local private key and use it to sign transactions.

Hosted Private Key

This is a legacy way to use accounts when working with unit test backends like web3.providers.eth_tester.main.EthereumTesterProvider or Anvil. Calling web3.eth.accounts gives you a predefined list of accounts that have been funded with test ETH. You can use any of these accounts with use send_transaction() without further configuration.

In the past, around 2015, this was also a way to use private keys in a locally hosted node, but this practice is now discouraged.


Methods like web3.eth.send_transaction` do not work with modern node providers, because they relied on a node state and all modern nodes are stateless. You must always use local private keys when working with nodes hosted by someone else.

Some Common Uses for Local Private Keys

A very common reason to work with local private keys is to interact with a hosted node.

Some common things you might want to do with a Local Private Key are:

Using private keys usually involves w3.eth.account in one way or another. Read on for more, or see a full list of things you can do in the docs for eth_account.Account.

Creating a Private Key

Each Ethereum address has a matching private key. To create a new Ethereum account you can just generate a random number that acts as a private key.

  • A private key is just a random unguessable, or cryptographically safe, 256-bit integer number

  • A valid private key is > 0 and < max private key value (a number above the elliptic curve order FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFE BAAEDCE6 AF48A03B BFD25E8C D0364141)

  • Private keys do not have checksums.

To create a private key using and command line you can do:

python -c "from web3 import Web3; w3 = Web3(); acc = w3.eth.account.create(); print(f'private key={w3.to_hex(acc.key)}, account={acc.address}')"

Which outputs a new private key and an account pair:

private key=0x480c4aec9fa..., account=0x9202a9d5D2d129CB400a40e00aC822a53ED81167
  • Never store private key with your source. Use environment variables to store the key. Read more below.

  • You can also import the raw hex private key to MetaMask and any other wallet - the private key can be shared between your Python code and any number of wallets.

Funding a New Account

If you create a private key, it comes with its own Ethereum address. By default, the balance of this address is zero. Before you can send any transactions with your account, you need to top up.

  • For a local test environment, any environment is bootstrapped with accounts that have ETH on them. Move ETH from default accounts to your newly created account.

  • For public mainnet, you need to buy ETH in a cryptocurrency exchange

  • For a testnet, you need to [use a testnet faucet](

Reading a Private Key from an Environment Variable

In this example we pass the private key to our Python application in an environment variable. This private key is then added to the transaction signing keychain with Signing middleware.

If unfamiliar, note that you can export your private keys from Metamask and other wallets.


  • Never share your private keys.

  • Never put your private keys in source code.

  • Never commit private keys to a Git repository.


import os
from eth_account import Account
from eth_account.signers.local import LocalAccount
from web3 import Web3, EthereumTesterProvider
from web3.middleware import construct_sign_and_send_raw_middleware

w3 = Web3(EthereumTesterProvider())

private_key = os.environ.get("PRIVATE_KEY")
assert private_key is not None, "You must set PRIVATE_KEY environment variable"
assert private_key.startswith("0x"), "Private key must start with 0x hex prefix"

account: LocalAccount = Account.from_key(private_key)

print(f"Your hot wallet address is {account.address}")

# Now you can use web3.eth.send_transaction(), functions
# with your local private key through middleware and you no longer get the error
# "ValueError: The method eth_sendTransaction does not exist/is not available

Example how to run this in UNIX shell:

# Generate a new 256-bit random integer using openssl UNIX command that acts as a private key.
# You can also do:
# python -c "from web3 import Web3; w3 = Web3(); acc = w3.eth.account.create(); print(f'private key={w3.to_hex(acc.key)}, account={acc.address}')"
# Store this in a safe place, like in your password manager.
export PRIVATE_KEY=0x`openssl rand -hex 32`

# Run our script

This will print:

Your hot wallet address is 0x27C8F899bb69E1501BBB96d09d7477a2a7518918

Extract private key from geth keyfile


The amount of available ram should be greater than 1GB.

with open('~/.ethereum/keystore/UTC--...--5ce9454909639D2D17A3F753ce7d93fa0b9aB12E') as keyfile:
    encrypted_key =
    private_key = w3.eth.account.decrypt(encrypted_key, 'correcthorsebatterystaple')
    # tip: do not save the key or password anywhere, especially into a shared source file

Sign a Message


There is no single message format that is broadly adopted with community consensus. Keep an eye on several options, like EIP-683, EIP-712, and EIP-719. Consider the w3.eth.sign() approach be deprecated.

For this example, we will use the same message hashing mechanism that is provided by w3.eth.sign().

>>> from web3 import Web3, EthereumTesterProvider
>>> from eth_account.messages import encode_defunct

>>> w3 = Web3(EthereumTesterProvider())
>>> msg = "I♥SF"
>>> private_key = b"\xb2\\}\xb3\x1f\xee\xd9\x12''\xbf\t9\xdcv\x9a\x96VK-\xe4\xc4rm\x03[6\xec\xf1\xe5\xb3d"
>>> message = encode_defunct(text=msg)
>>> signed_message = w3.eth.account.sign_message(message, private_key=private_key)
>>> signed_message

Verify a Message

With the original message text and a signature:

>>> message = encode_defunct(text="I♥SF")
>>> w3.eth.account.recover_message(message, signature=signed_message.signature)

Prepare message for ecrecover in Solidity

Let’s say you want a contract to validate a signed message, like if you’re making payment channels, and you want to validate the value in Remix or web3.js.

You might have produced the signed_message locally, as in Sign a Message. If so, this will prepare it for Solidity:

>>> from web3 import Web3

# ecrecover in Solidity expects v as a native uint8, but r and s as left-padded bytes32
# Remix / web3.js expect r and s to be encoded to hex
# This convenience method will do the pad & hex for us:
>>> def to_32byte_hex(val):
...   return Web3.to_hex(Web3.to_bytes(val).rjust(32, b'\0'))

>>> ec_recover_args = (msghash, v, r, s) = (
...   Web3.to_hex(signed_message.messageHash),
...   signed_message.v,
...   to_32byte_hex(signed_message.r),
...   to_32byte_hex(signed_message.s),
... )
>>> ec_recover_args

Instead, you might have received a message and a signature encoded to hex. Then this will prepare it for Solidity:

>>> from web3 import Web3
>>> from eth_account.messages import encode_defunct, _hash_eip191_message

>>> hex_message = '0x49e299a55346'
>>> hex_signature = '0xe6ca9bba58c88611fad66a6ce8f996908195593807c4b38bd528d2cff09d4eb33e5bfbbf4d3e39b1a2fd816a7680c19ebebaf3a141b239934ad43cb33fcec8ce1c'

# ecrecover in Solidity expects an encoded version of the message

# - encode the message
>>> message = encode_defunct(hexstr=hex_message)

# - hash the message explicitly
>>> message_hash = _hash_eip191_message(message)

# Remix / web3.js expect the message hash to be encoded to a hex string
>>> hex_message_hash = Web3.to_hex(message_hash)

# ecrecover in Solidity expects the signature to be split into v as a uint8,
#   and r, s as a bytes32
# Remix / web3.js expect r and s to be encoded to hex
>>> sig = Web3.to_bytes(hexstr=hex_signature)
>>> v, hex_r, hex_s = Web3.to_int(sig[-1]), Web3.to_hex(sig[:32]), Web3.to_hex(sig[32:64])

# ecrecover in Solidity takes the arguments in order = (msghash, v, r, s)
>>> ec_recover_args = (hex_message_hash, v, hex_r, hex_s)
>>> ec_recover_args

Verify a message with ecrecover in Solidity

Create a simple ecrecover contract in Remix:

pragma solidity ^0.4.19;

contract Recover {
  function ecr (bytes32 msgh, uint8 v, bytes32 r, bytes32 s) public pure
  returns (address sender) {
    return ecrecover(msgh, v, r, s);

Then call ecr with these arguments from Prepare message for ecrecover in Solidity in Remix, "0x1476abb745d423bf09273f1afd887d951181d25adc66c4834a70491911b7f750", 28, "0xe6ca9bba58c88611fad66a6ce8f996908195593807c4b38bd528d2cff09d4eb3", "0x3e5bfbbf4d3e39b1a2fd816a7680c19ebebaf3a141b239934ad43cb33fcec8ce"

The message is verified, because we get the correct sender of the message back in response: 0x5ce9454909639d2d17a3f753ce7d93fa0b9ab12e.

Sign a Transaction

Create a transaction, sign it locally, and then send it to your node for broadcasting, with send_raw_transaction().

>>> transaction = {
...     'to': '0xF0109fC8DF283027b6285cc889F5aA624EaC1F55',
...     'value': 1000000000,
...     'gas': 2000000,
...     'maxFeePerGas': 2000000000,
...     'maxPriorityFeePerGas': 1000000000,
...     'nonce': 0,
...     'chainId': 1,
...     'type': '0x2',  # the type is optional and, if omitted, will be interpreted based on the provided transaction parameters
...     'accessList': (  # accessList is optional for dynamic fee transactions
...         {
...             'address': '0xde0b295669a9fd93d5f28d9ec85e40f4cb697bae',
...             'storageKeys': (
...                 '0x0000000000000000000000000000000000000000000000000000000000000003',
...                 '0x0000000000000000000000000000000000000000000000000000000000000007',
...             )
...         },
...         {
...             'address': '0xbb9bc244d798123fde783fcc1c72d3bb8c189413',
...             'storageKeys': ()
...         },
...     )
... }
>>> key = '0x4c0883a69102937d6231471b5dbb6204fe5129617082792ae468d01a3f362318'
>>> signed = w3.eth.account.sign_transaction(transaction, key)
>>> signed.rawTransaction
>>> signed.hash
>>> signed.r
>>> signed.s
>>> signed.v

# When you run send_raw_transaction, you get back the hash of the transaction:
>>> w3.eth.send_raw_transaction(signed.rawTransaction)  

Sign a Contract Transaction

To sign a transaction locally that will invoke a smart contract:

  1. Initialize your Contract object

  2. Build the transaction

  3. Sign the transaction, with w3.eth.account.sign_transaction()

  4. Broadcast the transaction with send_raw_transaction()

# When running locally, execute the statements found in the file linked below to load the EIP20_ABI variable.
# See:

>>> from web3 import Web3, EthereumTesterProvider
>>> w3 = Web3(EthereumTesterProvider())

>>> unicorns = w3.eth.contract(address="0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359", abi=EIP20_ABI)

>>> nonce = w3.eth.get_transaction_count('0x5ce9454909639D2D17A3F753ce7d93fa0b9aB12E')  

# Build a transaction that invokes this contract's function, called transfer
>>> unicorn_txn = unicorns.functions.transfer(
...     '0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359',
...     1,
... ).build_transaction({
...     'chainId': 1,
...     'gas': 70000,
...     'maxFeePerGas': w3.to_wei('2', 'gwei'),
...     'maxPriorityFeePerGas': w3.to_wei('1', 'gwei'),
...     'nonce': nonce,
... })

>>> unicorn_txn
{'value': 0,
 'chainId': 1,
 'gas': 70000,
 'maxFeePerGas': 2000000000,
 'maxPriorityFeePerGas': 1000000000,
 'nonce': 0,
 'to': '0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359',
 'data': '0xa9059cbb000000000000000000000000fb6916095ca1df60bb79ce92ce3ea74c37c5d3590000000000000000000000000000000000000000000000000000000000000001'}

>>> private_key = b"\xb2\\}\xb3\x1f\xee\xd9\x12''\xbf\t9\xdcv\x9a\x96VK-\xe4\xc4rm\x03[6\xec\xf1\xe5\xb3d"
>>> signed_txn = w3.eth.account.sign_transaction(unicorn_txn, private_key=private_key)
>>> signed_txn.hash
>>> signed_txn.rawTransaction
>>> signed_txn.r
>>> signed_txn.s
>>> signed_txn.v

>>> w3.eth.send_raw_transaction(signed_txn.rawTransaction)  

# When you run send_raw_transaction, you get the same result as the hash of the transaction:
>>> w3.to_hex(w3.keccak(signed_txn.rawTransaction))