cannot send proper OP_RETURN transaction (with no address nor amount)

[wlmr]

Hi,

We are trying to create OP_RETURN transactions for storing hashes in the blockchain. These types of transactions should not need a a destination address for the ScriptPubKey, nor should they require any amount.

When trying to leave out the address we get this:

>>> id = key.send([("", 0.00, "btc")], message="hash")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/wlmr/.local/lib/python3.9/site-packages/bit/wallet.py", line 772, in send
    tx_hex = self.create_transaction(
  File "/home/wlmr/.local/lib/python3.9/site-packages/bit/wallet.py", line 708, in create_transaction
    unspents, outputs = sanitize_tx_data(
  File "/home/wlmr/.local/lib/python3.9/site-packages/bit/transaction.py", line 421, in sanitize_tx_data
    output_size = [len(address_to_scriptpubkey(o[0])) + 9 for o in outputs]
  File "/home/wlmr/.local/lib/python3.9/site-packages/bit/transaction.py", line 421, in <listcomp>
    output_size = [len(address_to_scriptpubkey(o[0])) + 9 for o in outputs]
  File "/home/wlmr/.local/lib/python3.9/site-packages/bit/transaction.py", line 458, in address_to_scriptpubkey
    get_version(address)
  File "/home/wlmr/.local/lib/python3.9/site-packages/bit/format.py", line 48, in get_version
    version = b58decode_check(address)[:1]
  File "/home/wlmr/.local/lib/python3.9/site-packages/bit/base58.py", line 74, in b58decode_check
    raise ValueError(
ValueError: Decoded checksum b'\x00' derived from "" is not equal to hash checksum b']\xf6\xe0\xe2'.

---

When trying to use the address of the sender:

>>> id = key.send([(key.address, 0.00, "btc")], message="hash")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/wlmr/.local/lib/python3.9/site-packages/bit/wallet.py", line 772, in send
    tx_hex = self.create_transaction(
  File "/home/wlmr/.local/lib/python3.9/site-packages/bit/wallet.py", line 721, in create_transaction
    return create_new_transaction(self, unspents, outputs)
  File "/home/wlmr/.local/lib/python3.9/site-packages/bit/transaction.py", line 721, in create_new_transaction
    outputs = construct_outputs(outputs)
  File "/home/wlmr/.local/lib/python3.9/site-packages/bit/transaction.py", line 485, in construct_outputs
    script_pubkey = OP_RETURN + len(dest).to_bytes(1, byteorder='little') + dest
TypeError: can't concat str to bytes

As soon as we change the amount to something bigger than 0, with the address pointing to the senders address, it goes through, however.

---

Is it possible to create a proper OP_RETURN transaction in some other way?

[KevNeff]

Hi there. I just started learning the bit library with the poster's exact use case in mind, to store hashes on the blockchain.

"

BTW I don't remember if we talked about this, but the other day some
people were mentioning secure timestamping. You want to be able to
prove that a certain document existed at a certain time in the past.
Seems to me that bitcoin's stack of blocks would be perfect for this.

Indeed, Bitcoin is a distributed secure timestamp server for
transactions. A few lines of code could create a transaction with
an extra hash in it of anything that needs to be timestamped.
I should add a command to timestamp a file that way.
"
~ Satoshi
https://mmalmi.github.io/satoshi/

This is an early Satoshi quote, but this interaction is now possible with the implementation of OP_RETURN transactions. Notably, they are done with zero value btc output and require no receiver. It would be really useful to leverage this implementation programmatically through your python library!