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Abstract-Researchers have proposed systems in which users utilize an eye tracker to enter passwords by merely looking at the proper symbols on the computer monitor in the appropriate order. This authentication method is immune to the practice of shoulder surfing: secretly observing the keystrokes of a legitimate user as he or she types a password on a keyboard. In this paper we describe the EyeDent system-in which users authenticate by looking at the symbols on an on-screen keyboard to enter their password. Existing eye-tracking based authentication systems require the user to dwell or press a trigger when looking at each symbol. Instead, in EyeDent, gaze points are automatically clustered to determine the user's selected symbols; this approach has the benefit of allowing users to authenticate at their natural speed, rather than with a fixed dwell time. Additionally, the absence of a visible trigger does not divulge the number of symbols in the password.Results from preliminary investigations indicate that quick (3 seconds for a 4 digit PIN) authentication is possible using this scheme, but more work is needed to account for calibration error, and to dynamically adapt system parameters to the characteristics of individual users.

The role of mammal-eating, or transient, killer whales Orcinus orca in the decline of various marine mammal populations in Alaska is controversial and potentially important in their recovery. Classical predator-prey models are insufficient to describe the dynamics of a single predator on the number of prey types known for these predators, and there are few populationlevel data that could be used to parameterize such models. As an heuristic framework for this more complicated system, we developed an agent-based model of killer whales with plausible energetics and behavior. We calibrated and validated the model using single-prey scenarios (a community of generic 'Seals') against published expectations for prey consumption rates, killer whale group dynamics, and demography. We then explored the emergent properties of single-prey models and of 3-prey models using the 'Seals' as primary prey, a generic small population of 'Sea Lions', and seasonally available large 'Whales'. The single-prey model gave results that were intuitively reasonable and responsive to underlying parameters but were also sensitive to encounter/killing rates, as expected in classic predator-prey models with similar parameters. However, the dynamics included long time lags (~30 yr) with strong shifts in predator age structure and vital rates. In multi-prey scenarios in which the importance of seasonally available large whale prey was manipulated, large whale prey had the potential to augment killer whale numbers somewhat but had a minimal effect on the overall dynamics, whereas perturbing the carrying capacity of the primary prey created strong numeric shifts in killer whale population size and consequent indirect effects on both alternate prey. No predictive utility is suggested due to the absence of such elements as spatial realism, explicit prey-switching and more realistic prey structure, but the models suggest that we consider more complicated numerical dynamics of killer whales in discussions of their impact on prey.

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