Is it possible in Ethereum to issue multi-sig transactions which are not implemented on smart contract level but instead via signing, similar to Bitcoin?
The following would be an example of a multi-sig transaction - might work in practice differently, just for sake of argument:
signature1 = sign(privateKey1, message);
signature2 = sign(privateKey2, signature2);
Background + Motivation: I am doing a thought experiment whether or not it makes sense to block transactions that have code associated (instead of being private key-controlled). E.g.: If one issued a
centralized-fiat-token and wants to ensure KYC-compliance, one might want to only allow these
centralized-fiat-token to be sendable to and from KYC-approved addresses. However, these addresses could actually be controlling a multi-sig wallet or even be a proxy contract that gives other non-KYC-compliant parties access to these tokens. To prevent that, one could limit transferrability to only approved addresses that do not have any associated code.
[This is obviously a bad idea because, 1) e.g. the mist wallet is/was a code-controlled wallet and as such be locked-out, 2) I might want to move funds to another account that I control myself, without undergoing (parts of) the KYC procedure again.]
If we could show that multi-sig transactions are anyway possible even without code in multi-private-key scenarios, then the whole argumentation of blocking code-controlled addresses would break down.