The Casa Keymaster system with 3-of-5 Key Shield multisig is designed to protect large Bitcoin balances ($100k to $1mil and up). Since we are securing large balances, our 3-of-5 Key Shield multisig is designed to fill a niche as a premium, high-security product that is more risk-averse than most other competing consumer crypto storage systems.
High security is not “maximum security”, and chasing perfect security is a security hazard. More security can always be purchased at a greater cost of money and time. But some of the most involved systems we have seen involve dozens of hours of tedious and error-prone effort to set up. With overly complex systems, there is a danger that users will give up or get lazy momentarily, leaving them less secure. And with added complexity there is increased danger of user error leading to catastrophic loss.
We designed 3-of-5 Key Shield to protect against as many threats as possible while still leaving Keymaster with an excellent user experience.
We consider not only threats that are present now, but threats that are likely to occur in the future. As the popularity of 3-of-5 Key Shield grows and/or the value of bitcoin increases, the incentives for attackers will also increase. Attacks that are uncommon and unprofitable now will become profitable. We anticipate this in setting our security standard.