The proliferation of smart gadgets, appliances, mobile devices, PDAs and sensors has enabled the construction of ubiquitous computing environments, transforming regular physical spaces into "Active Information Spaces" augmented with intelligence and enhanced with services. This new exciting computing paradigm promises to revolutionize the way we interact with computers, services, and the surrounding physical spaces, yielding higher productivity and more seamless interaction between users and computing services. However, the deployment of this computing paradigm in real-life is hindered by poor security, particularly, the lack of proper authentication and access control techniques and privacy preserving protocols. We propose an authentication framework that addresses this problem through the use of different wearable and embedded devices. These devices authenticate entities with varied levels of confidence, in a transparent, convenient, and private manner, allowing the framework to blend nicely into ubiquitous computing environments.