Visit the following sites:
Authentication
https://www.keytrac.net/en/tryout/authenticate
Password sniffing
Physical Access
DNS enumeration
host <domin>
nmap -T4 -p 53 --script dns-brute <domain>
dnsrecon -d <domain> -n 144.38.192.3
dnsrecon -r 144.38.192.3-144.38.192.200
Rainbow tables Salt vs no salt
openssl passwd -1 -salt pepper
or
openssl passwd -1