Perhaps you _can_ do it that way, but you can also just use m-of-n cryptography (e.g. Shamir's Secret Sharing Scheme) to split your private key. See http://doc

Perhaps you _can_ do it that way, but you can also just use m-of-n cryptography (e.g. Shamir's Secret Sharing Scheme) to split your private key. See http://docs.electrum.org/en/latest/multisig.html http://docs.electrum.org/en/latest/multisig.html for an example, and https://en.bitcoin.it/wiki/Multisignature https://en.bitcoin.it/wiki/Multisignature for more background (including links to SSSS). You don't need a smart contract to achieve this. I suppose it's more convenient since your co-signers can just submit their M signatures onto the blockchain, instead of having to collaborate offline to generate a valid signed block. But putting the multisig logic into a smart contract is quite obviously not fail-safe, as these vulnerabilities show.