Decrypting Login Keychain encrypted with smartcard
Solution 1:
If you performed your initial login and profile setup using your "smartcard" then your login keychain password will be your PIN.
If you find this is not the case (& no passwords you enter work either), you may just have to trash your login keychain by deleting the login.keychain & login.keychain-db files from ~/Library/Keychains, restarting, logging in again with your "smartcard" & PIN to create a new login keychain, the password for which will then be the same as your PIN.