Analogue web3.eth.accounts.sign (from web3js) in web3py

Question

There is a function web3.eth.accounts.sign in the implementation of web3js. But I cannot find the exact equivalent in web3py I don't see this. I found something similar to this — the signHash function (link https://web3py.readthedocs.io/en/stable/web3.eth.account.html#sign-a-message). This documentation says that the same hashing mechanism, but as a result, execution returns not the same as in web3js (web3.eth.accounts.sign).

I used this function in web3js to get signature (and then using ECDSA library (on Solidity) to get signer. On web3js works correctly (but on web3py - no). I connect to test network (ropsten) via Infura.

On web3js (where msg - what is signed):

let signature = await web3.eth.accounts.sign(msgHash, '0x' + privateKeyUser);
console.log('signature ='+signature.signature);

On web3py (I try, but doesn't work):

signature = web3.eth.account.signHash(msgHash, '0x' + privateKeyUser)
print('signature ='+signature.signature.hex())

And for example in variable "msgHash" value: 0x058c3b4c8e5dc4632b5c6b861b2c1861d53e426dc673c907ddf2651942b0f230 And at the output of web3js function (web3.eth.accounts.sign), we get signature: 0xd19241ed816026e846c8511e03a468aa6e038165ecb3c2229eee38b04c64b235408389dfad2b65d776dba236e7de1b63fdb6b2579e70c4ce9ad1b09a35da96521c And this is the correct value. Web3py has other value.

What is exact analogue in web3py of how this web3.eth.accounts.sign function works in web3js? Thank you!

Answer 1

Since you mentioned in comments that you're open to using web3.py v5, here is the v5 approach to sign a message:

from eth_account import Account, messages

msg_hash_hex = "058c3b4c8e5dc4632b5c6b861b2c1861d53e426dc673c907ddf2651942b0f230"
private_key_hex = "b25c7db31feed9122727bf0939dc769a96564b2de4c4726d035b36ecf1e5b364"

#// This part prepares "version E" messages, using the EIP-191 standard
message = messages.encode_defunct(hexstr=msg_hash_hex)

#// This part signs any EIP-191-valid message
signed_message = Account.sign_message(message, private_key=private_key_hex)
print("signature =", signed_message.signature.hex())

If you'd like to know more about EIP-191, check out the original EIP-191 writeup. It's short and readable.

That snippet is equivalent to the javascript:

msgHash = "0x058c3b4c8e5dc4632b5c6b861b2c1861d53e426dc673c907ddf2651942b0f230"
privateKeyUser = "b25c7db31feed9122727bf0939dc769a96564b2de4c4726d035b36ecf1e5b364"

// web3.js sign() *only* supports "version E" EIP-191 signing
// so it adds the preamble for you.
let signature = await web3.eth.accounts.sign(msgHash, '0x' + privateKeyUser);
console.log('signature ='+signature.signature);

Note that the javascript sign() method "signs arbitrary data" rather than a message hash. So although you appear to be hashing it first, you could sign the original message instead.

In the python version, prepare the original message for signing with: encode_defunct(text=original_message).

Answer 2

It is hard to tell without seeing the content of all variables, including keys.

But my gut feeling is that you are mixing raw bytes and hexadecimal ASCII strings - some of the variables are not what you think they are.

If possible can you edit your question with a lot of prints and output to compare?

Answer 3

For anyone came here with web3.py < v5:

Use defunct_hash_message on the message before using signHash.

from eth_account.messages import defunct_hash_message
prepared_message = defunct_hash_message(primitive=msgHash)
signature = web3.eth.account.signHash(prepared_message, '0x' + privateKeyUser)
print('signature =' + signature.signature.hex())