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Are there any op codes or combination of opcodes that can be used instead of a digital signature when creating a transaction?
Can op codes be used instead of signatures?
Answers
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Existing signature schemes in Bitcoin are already implemented as opcodes (OP_CHECKSIG and OP_CHECKMULTISIG in particular), so this question's formulation seems a bit off.
If you don't mind a transaction whose outputs can be taken by anyone, this is trivial - you can just create an output with a script that does not use any signature checking opcodes.
Perhaps what you want to ask is Is there a way to create secure transactions without using any of the explicit digital signature opcodes?.
The answer to that is almost certainly no. You would effectively need to implement a digital signature scheme by hand, rather than relying on the provided ones. Digital signature schemes are remarkably complicated, and likely far beyond what is possible inside Bitcoin's current scripting language.
So is there no way to prove ownership of utxos without signing a transaction? – Errol – 2018-03-24T21:05:35.643
You can sign an arbitrary message with one or more private keys that can be verified against a bitcoin address or redeem script, thus proving you can access all UTXOs accessible by that address or redeem script – Raghav Sood – 2018-03-24T21:10:27.760
Can custom scripts be used to bypass the need for a sigbature? – Errol – 2018-03-24T21:13:16.963
@Errol Proving ownership of UTXOs is completely unrelated to your question above (ownership is a legal construction, and is not the same as access to the private key). – Pieter Wuille – 2018-03-24T22:52:00.563
2@Errol Based on several question I see you asking, maybe you're missing this: a script is Bitcoin is a description of the conditions under which the money can be moved. Every script will generally at least specify a digital signature with one or more keys are required. But there is no concept of ownership or control beyond what the script states. There is no way to bypass the script, as the script defines how the coins can be used. – Pieter Wuille – 2018-03-24T22:56:27.923
Is it possible to alter the conditions of the script? – Errol – 2018-03-24T23:14:21.190
@Errol No, that would defeat the purpose. Read again what I said: the script is the definition of how the money can be spent. Being able to modify that (without spending) would be theft. Transactions are the only way to modify what amounts are under control of which conditions. – Pieter Wuille – 2018-03-24T23:37:14.780