Abstract: “Computer security is largely supported by passwords forming the principal part of the authentication process. Visual passwords have been proposed as a more secure alternative to alphanumeric passwords but have not as of yet been readily adapted due to the problems associated with current implementations of visual passwords. One of the main issues in the implementation of visual password schemes is the type of password images used. To address the issue of designing and using secure password images, we present a model of a shape grammar supported visual password scheme generating password images that adhere to a specific syntax or set of rules. We present a design of a grammar model which is well adaptable for implementations of visual password scheme images and images with a rule based structure.”

Keywords: grammars, shape grammars, visual password authentication, theoretical computer science