A method involving a secret sequence after which a user is authenticated to use certain services. For example: SSH. Considered security through obscurity by some critics because of vulnerabilities in the security meassure. One of these vulnerabilities often heard is that the sequence isn’t really secret; e.g. it is sniffable.
- Newsforge: A critique to port knocking (http://software.newsforge.com/article.pl?sid=04/08/02/1954253).
TakeDown.NET -> “Port-Knocking”