is not this WoT just about "i fully trust Dr A's public key is P1 because he gave it to me personally. i trust Dr A's sibling's public key is P2 because i've found it somewhere and it's cryptographically signed with P1. so i'm highly confident that this cryptographically signed message is from Dr A's sibling as long as neither P1 or P2 compromised or misused in the meanwhile." ?