Further reading

• Masking syntax for John: https://github.com/magnumripper/JohnTheRipper/blob/bleeding-jumbo/doc/MASK
• Rules syntax for John: http://www.openwall.com/john/doc/RULES.shtml
• Overview of capture auxiliary modules in Metasploit: https://www.offensive-security.com/metasploit-unleashed/server-capture-auxiliary-modules/