The core of private key operations doesn't require access to the whole certificate. A private key subsystem only needs to handle the cryptographic key material.
### OpenPGP card for private keys
[OpenPGP card](https://en.wikipedia.org/wiki/OpenPGP_card) devices are a type of hardware security device. They are one popular way to handle OpenPGP private key material. These devices do not store the full OpenPGP certificate.