Abstract
M-Commerce will not prosper without reliable and usable security concepts. Concepts which are not prone to scare users away from utilizing mobile applications, secured by complicated and cryptic mechanisms are the essential building blocks of M-Commerce. This publication specifies a highly usable security solution for a mobile worker by introducing a so-called proximity device. It is a physically small device, for instance unobtrusively wearable as a ring, cryptographically proving its presence to a security module in order to facilitate use of critical functionality. The paper introduces an architecture based on a security module which is implemented as tamper resistant hardware such as a smart card. The security module operates as expected if the proximity device can cryptographically prove its presence within a safe physical proximity. The user benefits from the proximity device in many ways, for instance it is no longer necessary to perform frequent activation processes for the security module and one stolen device alone is no longer usable for a thief.