Smart cards are convenient and secure. They protect sensitive information (e.g., private keys) from malicious applications. However, they do not protect the owner from abuse of the smart card: An application could for example cause a smart card to digitally sign any message, at any time, without the knowledge of the owner. In this paper we suggest that small, hand-held computers can be used instead of smart cards. They can communicate with the user directly and therefore do not exhibit the above mentioned problem. We have implemented smart card functionality for a 3COM PalmPilot. Our implementation is a PKCS#11 module that plugs into Netscape Communicator and takes about 5 seconds to sign an email message. Generalizing from this experience, we argue that applications that are split between a PC and a hand-held device can be more secure. While such an application remains fast and convenient to use, it gains additional security assurances from the fact that part of it runs on a trusted device.

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