I wouldn’t use the Yubico HSM, because I think it misses a feature that would IMO add considerable value: an enforced CT-style log. If I were paying for a cor

I wouldn’t use the Yubico HSM, because I think it misses a feature that would IMO add considerable value: an enforced CT-style log. If I were paying for a corporate root of trust, I would want very strong auditability. Set it up so that the HSM does not release a signature until presented with an SCT. Make it impossible for buggy or compromised host software to create bad certificates without being detected. A hardware HSM is not magic or even especially complex. Java cards can do it (slowly). Yubikeys can do it. Other vendors’ devices can do it. Lots of microcontrollers can do it as long as you don’t need resistance to complex physical attack. A startup in this space should seriously consider building its own.