[daave]

You're certainly more of an authority on it than I, so I trust when you say most schemes don't keep long-term keypairs around; but of the two companies I've worked at that use SSH CAs: one used Teleport, and the other had long-lived keypairs, but fairly-short-lived certificates -- you had to get your public key re-signed each day. They used Yubikeys to store (or maybe just unwrap?) the private key material during the SSH handshake; much as a TPM or the Secure Enclave could be used to do this.

[camgas]

My experience (over maybe 10 years of using SSH-CAs) was similar, I mean by using long-term key pairs (mostly for humans) and shorter certificates. I can imagine secretive to be a very useful tool for SSH-CAs and other uses. I also like the fact that you can't import a key, makes it pretty clear that A- it's a specific device, and B- there is a human adding their bio info to unlock it.

[tptacek]

Your experience of SSH CAs is different from mine (that doesn't make it wrong). My experience is that the major motivation for SSH CAs is linking SSH authentication to MFA SSO. The long-lived secrets here are the MFA secrets.