Keychain is an excellent way of making SSH passwordless connections between systems that you regularly connect to.
Installation is simple under Gentoo, you will already have the sshd installed as part of net-misc/openssh, its then just a case of installing keychain itself…
emerge -av keychain
To ensure that your password is requested you can use SSH askpass or the AskPass Fullscreen to ensure you are
Rather than duplicating what has already been written please follow the instructions at the Gentoo Linux Keychain Guide.