If your concern is that you don't want to lose all your coins because your entire seed was kept in one place, then why not implement a multi-sig solution instead? Much better than having to split keys and deal with weakened security?
multi-sig is one option, but is more expensive to get a multi-sig transaction confirmed.
Splitting keys up and storing them in two locations will increase security from that of the location with the lessor security that holds each of the 12 words.
it will increase the security but also it will decrease it. the increase however is tiny while the decrease is gigantic so the total is not acceptable.
note that what i said above about splitting was about splitting the encrypted result not the seed itself. when you split the seed your choice is still from 2048 words but when you split the encrypted result your choice is the missing bytes. so for example if you split a 32 byte result into two 16 bytes and one part is compromised you still have 2^128 choices to then decrypt! and that is only for the paranoid.
You are assuming that half the seed will be compromised, but this is not the case.
Let me explain it this way:
I am going to use a vault located at 555 Main Street, Springfield, US. If the vault is broken into:
- if I keep my entire seed in this vault, my private keys are instantly compromised and known to the thief
- if I keep 1/2 of my seed in this vault, my private keys are less secure than they previously were, and I have some time to move any coins secured by these private keys before the thief can reasonably know my private keys
As of prior to when the vault is broken into my private keys are equally safe in both scenarios.
