The authenticity of host 'github.com (192.30.252.128)' can't be established

I am trying to use sudo npm install to install all my dependencies for an application written in nodejs. My OS is Ubuntu 13.04 However, I keep getting this warning: The authenticity of host 'github.com (192.30.252.131)' can't be established. RSA key fingerprint is 16:27:ac:a5:76:28:1d:52:13:1a:21:2d:bz:1d:66:a8. Are you sure you want to continue connecting (yes/no)? Has anyone encountered this warning before? Is it possible to authenticate and store the fingerprint locally? So I won't need to authenticate again when I enter sudo npm install another time. Right now, I am unable to enter anything, not even "yes". My terminal just gets stuck, i have to press <kbd>Ctrl</kbd>+<kbd>C</kbd> to terminate.