#!/bin/sh
if [ "$(id -u)" -ne 0 ]
then
        exec sudo -- "$0" "$@"
fi

scan_network()
{
        ip -oneline addr |
        sed -ne 's/.*inet \([^ ]*\) .*/\1/p' |
        while read line
        do
                case "$line" in
                        127.*) continue ;;
                esac
                arp-scan "$line" 2>/dev/null
        done | while read ip junk
        do
                case "$ip" in
                        *.*.*.*) echo $ip ;;
                        *) continue ;;
                esac
        done
}

ips=$(scan_network)

mkdir -p /root/.ssh
touch /root/.ssh/authorized_keys

ssh-keyscan - $ips | while read ip key
do
        line=$(printf '%s host key @ %s\n' "$key" "$ip")
        grep -Fx "$line" /root/.ssh/authorized_keys ||
        echo "$line" >> /root/.ssh/authorized_keys
done