GENERATING A KEY FOR USE AS A SHARED SECRET

摘要

A communications device (110) for generating a key for use as a shared secret in communications with another communications device (120) is provided. Each of the communications devices (110, 120) comprises a sensor array (111, 121) for measuring a spatially-varying magnetic field (320) originating from a first spatially-varying density of metallic particles comprised in a first battery (113), when subjected to an excitation magnetic field, and processing means operative to acquire a set of values from the sensor array (111, 121), which set of values represents the spatially-varying magnetic field (320), and to derive the key from the set of values. The excitation magnetic field (310) is generated by a magnetic-field generator (114) comprised in one of the communications devices (110, 120). Thereby, the two communications devices (110, 120) may, when in proximity, generate identical keys by probing the spatially-varying density of metallic particles comprised in the first battery (113).