-u

The option -u is used for fetching the ssh-rsa public keys, when passing a username for example:

$ ssh-vault -u alice

It will try to fetch the keys from github.com.

-u https://…

In case the keys are not in github, and url can be passed, for example:

$ ssh-vault -u https://launchpad.net/~user/+sshkeys

Using gitlab:

$ ssh-vault -u https://gitlab.com/<user>.keys

-k N

There may be cases where the user has more than one key in this keys the option -k helps to specify what key to use, for example if we want to send something to user bob using his second key, this would be used:

$ ssh-vault -u bob -k 2 create file

or

$ ssh-vault -u https://launchpad.net/~bob/+sshkeys -k 2 create file