As in all good Hollywood movies there is a secret way into the castle – maybe a tunnel, a postern gate or a small iron grille over a sewer – which is known only to the people who built it. This is the software ‘backdoor’ created by the original coders of the system which still exists but has been forgotten about. Also bear in mind that the wagons bringing essential goods into your castle are a vulnerable element. In the Hollywood movie, the enemy hijack the wagons and enter the castle in disguise. In a cyber context, this is known as a Trojan attack, named after the Trojan horse that concealed Greek warriors in the Iliad.
The castle model of cyber security is a useful way of illustrating some simple cyber security concepts, but it has a major flaw which is this – where do you put the wall? As the world becomes both more mobile and more interconnected, it is increasingly hard to draw the line between inside and outside from a system standpoint. This issue, known rather clumsily as de-perimeterization, is a big challenge for security professionals.
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