Fedora Magazine - https://fedoramagazine.org/fedora-28-better-smart-card-support-openssh/
Smart card support was introduced around 2010 with OpenSSH 5.4. The inital scope was restricted to the RSA keys — the only supported key type at that time in OpenSSH — other than legacy DSA keys. Previously, users needed to specify the PKCS#11 driver for the smart card. Additionally, the OpenSSH client had to query the server with all the stored keys in the card, until an acceptable key was found. This slowed down authentication, and reveals public keys to the server that might not be necessary (e.g., if we have a single card with keys for distinct servers).