So you need 1 of n private-keys to get your money back if the scammer sent it to any other address?
How long will that coins be locked up in the second layer before being able to withdraw it?
Some of these features can be provided without the need for a second layer. Providing multiple keys (N-of-N-1) will make the sending task more difficult and thus the same level of protection as you provide.
With CoinVault smart contracts unlocking and spending are two distinct events. And in case some of your private keys but not all are stolen, you need 1 more key than the hacker has to divert your Bitcoin to another secure address.
For example, Alice locked her Bitcoin using 5 keys inside a CoinVault smart depository contract and 3 of these keys were later stolen by hackers. Ubiquitous Multisig fails at this point. However, with CoinVault the hackers can provisionally unlock and attempt to spend from the contract using the 3 stolen keys but then Alice can intervene and divert the same bitcoin to another secure address using any 4 keys (3+1) from the 5 keys she used to lock her bitcoin to begin with.
We achieve this by requiring progressively more time when using fewer keys to spend from our smart contracts after unlocking them. And unlocking happens on-chain by broadcasting an intermediate provisional transaction, so Alice will know and will have sufficient time (prechosen) to take remedial steps.
In the above example, Alice can unlock and spend from the contract immediately if she uses all 5 of the 5 keys.
But anyone including Alice can spend only after 1000 blocks (chosen by Alice during setup) are created on the bitcoin blockchain after the block confirming the intermediate provisional transaction when using just 4 of the 5 keys.
Similarly anyone including Alice can spend only after 2000 blocks (chosen by Alice during setup) are created on the bitcoin blockchain after the block confirming the intermediate provisional transaction when using just 3 of the 5 keys.
And this block interval between unlocking transaction and spending transaction grows further as we use fewer and fewer keys.
All this gives Alice an opportunity to intervene and take remedial steps when necessary.
Of course you can always require n of n keys or n-1 of n keys in a simple multisig transaction to achieve similar security but this makes your Bitcoin vulnerable to loss of keys which is another big problem. Co-signers can disappear or hold you bitcoin hostage in simple multisig but with coinvault many such contingencies can be avoided. As long as you have more keys accessible than the adversaries your bitcoin can be recovered.
