WordPress.org

The Perfect Paper Passwords plugin for WordPress gives you free multifactor authentication for your WordPress blog.

The multifactor authentication requirement can be enabled on a per user basis, You could enable it for your administrator account, but login as usual with less privileged accounts.

The Perfect Paper Passwords system itself was created by Steve Gibson, https://www.grc.com/ppp

This plugin requires the SHA256 hashing algorithm, the BCMath library and Mcrypt/AES-128 (Rijndael-128) to be available in your PHP installation, it's not possible to activate the plugin without