I don't know on Ethereum, but you can easily add short texts into Bitcoin transaction.
Yeah, I'm aware of that but that is not what I was looking for. Thanks for your inputs though.
actually you don't even need OP_Return if the option doesn't exist, you just have to view transactions differently. a transaction is jut a data structure with different parts that we interpret differently. for instance the first 4 bytes of a transaction is interpreted as a number which we call "version".
so in order to put "data" in a transaction you just have to find a field in your tx that allows you to enter data. in a transaction this can be the output. with OP_Return it becomes easier since it is designed for data but you can still do it with other OPs too. for instance the regular P2PKH outputs can be used (assuming OP_Return doesn't exist). you just have to change the pushed data to the value you like.
example: if you pay any amount to this address: 18L1ocUNq8EKJu1UHu92HKUk4jeXL9eXoL you are technically putting your bitcointalk username (Patatas) in the blockchain because if you look at the transaction's actual data you can see that this address is actually stored like this as an output:
76a914506174617461730000000000000000000000000088ac
or in more human readable format:
OP_DUP OP_HASH160 <Patatas(nullpaded)> OP_EQUALVERIFY OP_CHECKSIG
ps. obviously any amount sent to this address is lost because it is a burn address.
That is something I will consider. However, for every transaction say the transaction creator will be entering data. How hard it is to achieve this on a programming level and of course on ETH chain. Will the above scenario work for a smart contract as well?