If you have ssh with keys for authentication setup on your system, and you use vagrant then you can combine the two to have all your ssh keys automatically shared with your vagrant machine
vim ~/.ssh/config
Host                    192.168.x.x
ForwardAgent           yes

Inside your vagrant file, add the line:

config.ssh.forward_agent = true

Then, inside your host machine, run

ssh-add

to start the ssh agent on your host machine.

Then run ssh-add on the vagrant box.

You can even automate the ssh-add on your provisioning scripts with the following:

echo "ssh-add" >> /home/vagrant/.bash_profile

This way, every time you vagrant up your machine will be ready to ssh into any system you have configured in your host without the need for passwords (think deploying to staging servers)