Please where can 40 byte OP_RETURN transaction be used?
All you need to do is make a txn with an OP_RETURN script. Just create a raw txn, sign, and broadcast. The spec can be found by searching around; I don't have a link at the moment.
The easiest way to create OP_RETURN transaction is through coinb.in, The steps are -
1. Go to
https://coinb.in/#newTransaction or download it from
github for off-line usage.
2. Paste in your address, then click load to fetch received transactions/unspent outputs. (Internet connection needed)
3. Check the INPUTS you want to use.
4. Click on advance options, check Null Data field
- Allow data to be sent within the transaction and stored in the blockchain by using OP_RETURN.
5. Open the OUTPUTS tab, create a transaction, probably to your own address. In amount field, subtract fees (0.0001 BTC).
6.
Create another transaction, this time write hex data in place of address. Fill-in 0 in the amount field.7. Carefully check fees, then click submit to CREATE TRANSACTION.
8. Copy this transaction, in the SIGN tab, and use your private key to sign.
9. Copy the signed transaction, VERIFY everything is correct, then BROADCAST it.
https://bitcoin.org/en/developer-guide#standard-transactionsNull data pubkey scripts let you add a small amount of arbitrary data to the block chain in exchange for paying a transaction fee, but doing so is discouraged. (Null data is a standard pubkey script type only because some people were adding data to the block chain in more harmful ways.)
Pubkey Script: OP_RETURN <0 to 40 bytes of data>
(Null data scripts cannot be spent, so there's no signature script.)
Note -1.
Currently coinb.in supports maximum of 39 bytes of Null Data.
2. No. of Hex alphabets (0-9,a-f) must be even.
