How do I base58 encode the chain ID using Python?

Question

When Tezos needs to sign a baking or endorsement operation payload, byte 0 will be a 0x01 for a baking operation or 0x02 for an endorsement operation. Bytes 1-5 in the operation payload contain the chain ID (otherwise known as Network), which can be encoded in base58 using this specification:

let chain_id = "\087\082\000" (* Net(15) *)

The resulting chain ID will be a string like NetXdQprcVkpaWU (the currently active mainnet chain ID as of Feb. 16th, 2019).

How do I convert the 4-byte field in bytes 1-5 into the base58 encoded Net(15) format using Vitalik's pybitcointools module?

I've tried using the script in scripts/b58_prefix.py to determine the appropriate magicbyte to pass to the bitcoin.bin_to_b58check function, but I'm not getting the appropriate result:

$ ./b58_prefix.py Net 4
15 5722583 [87L, 81L, 215L]

Here is my code:

def get_chain_id(self):
    chainid = bytes.fromhex(self.payload[2:10])
    return bitcoin.bin_to_b58check(chainid, magicbyte=5722583)

On zeronet, an endorsement payload looks like this: 023bb717ee882891d7be5b881cefa98946800e3d67b5d01b4237b3618709defb51ec37c3e100000518ae, where 3bb717ee is the chain id, but that converts to Net1BPz7FKbUqsY and it should be NetXSzLHKwSumh7 on zeronet.

Answer 1

Your magicbyte seems to be wrong. If you take the decimal byte values from the original, convert them to hex, then pad it with a leading zero, you get

>>> struct.unpack('>L', b'\x00\x57\x52\x00')[0]
5722624

This value should produce the expected result:

>>> payload = '023bb717ee882891d7be5b881cefa98946800e3d67b5d01b4237b3618709defb51ec37c3e100000518ae'
>>> mb = struct.unpack('>L', b'\x00\x57\x52\x00')[0]
>>> chainid = bytes.fromhex(payload[2:10])
>>> bitcoin.bin_to_b58check(chainid, magicbyte=mb)
'NetXSzLHKwSumh7'

Answer 2

It looks like you are only actually grabbing 2 bytes of data (4 hex chars). I verified this by decoding the result you got, and it only returning two bytes of data for the given magic byte.

Try making the following change:

def get_chain_id(self):
    chainid = bytes.fromhex(self.payload[2:10])
    return bitcoin.bin_to_b58check(chainid, magicbyte=5722583)

Answer 3

First of all, many thanks! You've helped me with solving the block signature mystery :) You can use pytezos.encoding package:

from pytezos.encoding import base58_encode

def get_chain_id(self):
    chainid = bytes.fromhex(self.payload[2:10])
    return base58_encode(chain_id, b'Net')