||Authentication services are vital features, which must be available in any type of communications networks. By now, using a combination of a user-name and a password togrant a user access to the provided services mainly solves authentication. As mobiledevices, such as mobile phones or small and portable computers, gain the market more andmore, they can be used as a key for authentication services. Using a short-range wirelesscommunication technology with ad-hoc-properties can solve the communication betweenthese devices. Technologies such as Bluetooth or Wireless Local Area Network arebecoming a communication standard on nearly any kind of mobile and stationary devices.Authentication can then be used to verify the identity, the members of the network pretendto be. Our goal is to use any kind of mobile device as a key for different applications orservices.This work describes the general requirements for security, authentication, and building upspontaneous networks for mobile personal communications. Additionally we show, howsuch an ad-hoc network can be build up by discovering and identifying other devices. Theusage of public key cryptography in combination with certificates then authenticates the previously discovered devices.