User physical interaction characteristics information or the way a user physically interacts with a device is analyzed to aid in authenticating a user of a device. User physical interaction characteristics information such as swipe speed, finger area, finger conductivity, finger angle, device angle, movement patterns, acceleration, etc., provide signatures that are distinctive for particular individuals and possibly unique if measured to a sufficiently high level of precision. In some examples, a device measures finger positions, finger pad sizes, moisture level, acceleration, displacement, and changes in finger pad size for a particular user and compares the measurements to physical interaction characteristics measured during subsequent usage of the device to verify that a user is an authorized user.