Actually bringing your own key is possible, but there are limitations.
A FROST signing share is a polynomial evaluation. If, say, 3 people join together each bringing their own fixed signing shares, there exists some quadratic polynomial that interpolates their shares. However, it's impossible to find a linear (degree-one) polynomial which does the same.
In practice, this means if `n` people BYOK, they can definitely create an `n` of `n` threshold key with FROST. They can then issue new shares to add more people to the FROST group if they wanted, to make it an `n` of `m` threshold.
I'm not sure about the security implications of what a DKG would look like if only SOME keys are fixed and others can be variable. That's a different ball game 😅
