> 1. Abstraction. For the non-expert, the only metaphor that works for PKI is that of physical security. The concept of a "key" as a series of characters or a file that must be protected must be replaced by an abstraction that allows users to protect it in the same way they understand how to protect a key or a wallet.

Do you mean something like the Yubikey USB dongle: https://www.yubico.com/products/yubikey-hardware/

[not associated, just referencing a 'physical' item that can be treated as a 'key' by non-experts]