I have found similar question for PIV (and not PGP)
I assume PIV and OpenPGP would work in similar ways. I also assumes that the GPG private key never leaves the Yubikey.
If these assumptions are correct then:
- at encryption: a symmetric key is generated and encrypted on the sending computer using the GPG public key, then message is encrypted on the sending computer using symmetric key
- at decryption: the symmetric key is decrypted on the yubikey using the GPG private key, then the message is decrypted on the receiving computer using the symmetric key
- when signing: the sending computer computes the fingerprint of the message and then the yubikey encrypt it using the GPG private key
Is it the case? And if not, is the Yubikey a bottleneck when dealing with large messages?