web3.py signing message

Question

I'm trying to create a signature using web3.py with the following

private_key = "0x..."
message = "0x..."

w3.eth.account.sign_message(encode_defunct(hexstr=message), private_key=private_key)

SignedMessage(
messageHash=HexBytes('0x0977453c547a8ec8b97e6960c174171c26cc316fe3eb42e9c1f43d906988f2f7'), 
r=3826115209918881089309465947057239465610262098443411688798455982011613167534, 
s=57607373686102894909527198656322533582090341098386235608665690313545458942055, 
v=27, 
signature=HexBytes('0x08758124b2dde0a220b9e86a982343f8daf868c1b3d99eade5c74a72cce3bfae7f5c9e3803b0bef93e2d55c08d0f428976712fbaeee8a40ab1c223b8c67c80671b')
)

But I'm not getting the correct output for verifying with erecover on chain. I'm comparing with the js version which is correct:

const signMessage = (types, values, signer) => {
  const message = web3.eth.abi.encodeParameters(types, values);

  const hash = web3.utils.keccak256(message);
  const { r, s, v } = web3.eth.accounts.sign(hash, signer);
  const signature = web3.eth.abi.encodeParameters(
    ["bytes32", "bytes32", "uint8"],
    [r, s, v]
  );

  return { message, signature };
};

{
  message: '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',
  hash: '0x2cf410e76a0941e26af6f72a6a8d1cd85dccb68013cb75f79d6953d64df67519',
  signature: '0x822093256039a3f9a7cfeaef298b437a48ce819fbe2595b74f8b00bed01553bc64524f75795487183f0db628859d5dae0c7c80ea2b1b6dd1331f9101052ad705000000000000000000000000000000000000000000000000000000000000001b'
}

The message I'm getting from the js side and the private key is being passed as a string, but I am not getting the same signature that I'm getting from the js version.

I looked at this and this as well as the docs and still am not sure how to do this.

Answer 1

The issue is two fold, one that the hash should be passed, not the message. The other is that the signature is returned packed.

w3.eth.account.sign_message(encode_defunct(hexstr=hash), private_key=private_key)

SignedMessage(
messageHash=HexBytes('0x3418e4d525f194127a8568abe10ce8e85baacfc3a1787c7146b7dc17b3da4d3a'), 
r=84118226279719248546434396845856688871337333924969201322918159090204879128334, 
s=18459783198555716597479201270128233159415607675680227670410186427526995028124, 
v=28, 
signature=HexBytes('0xb9f93a970439f33211fc5761ec7df5065eea37fb99b73ebc2f71d2fda3e8870e28cfddf5cdec9fcb3c6f4b6339258904b639e0975dd511da00e858ba9acca89c1c'))

You can see that the v value is packed in the signature, this must be unpacked.

Packed signature from web3.py

0xb9f93a970439f33211fc5761ec7df5065eea37fb99b73ebc2f71d2fda3e8870e28cfddf5cdec9fcb3c6f4b6339258904b639e0975dd511da00e858ba9acca89c1c

Versus unpacked

0xb9f93a970439f33211fc5761ec7df5065eea37fb99b73ebc2f71d2fda3e8870e28cfddf5cdec9fcb3c6f4b6339258904b639e0975dd511da00e858ba9acca89c000000000000000000000000000000000000000000000000000000000000001c

So just pad 62 0's before the 1c (28) or 1b (27).

signed_message = w3.eth.account.sign_message(encode_defunct(hexstr=hash), private_key=private_key)
signature = signed_message.signature.hex()
if signature[130:] == '1c':
    signature = signature[:130] + '000000000000000000000000000000000000000000000000000000000000001c'
else:
    signature = signature[:130] + '000000000000000000000000000000000000000000000000000000000000001b'
return signature