AN ENCODER/DECODER

摘要

An encoder/decoder comprises a spherical body (14) on which is provided a plurality of different letters and/or numerals. Connecting means in the form of three circular members sharing the same axis encompass the sphere, two defining two parallel sighting hoops (16) and the third defining a sighting ring (17). The connecting means are mounted on a support body so that relative rotation of the connecting means and the body (14) can be effected. In use, the body (14) is rotated until two specified indicia lie visually between the two sighting hoops (16) in a specified order. Then, one or more indicia are read from the sighting ring (17). The encoder/decoder may be used to protect computer software against copying and may also be used to hinder unauthorised access to remote computer systems. Thus, the number of individuals using a system can be limited to the number of keys in existence, by a preliminary section of program that, by interrogating the user, can determine whether he has in his possession a suitable encoder/decoder such as outlined above.