Strong authentication tokens for generating dynamic security values having an acoustical input interface for acoustically receiving input data are disclosed. The tokens may also include an optical interface for receiving input data and may have a selection mechanism to select either the acoustical or the optical input interface to receive data. A communication interface may be provided to communicate with a removable security device such as a smart card and the token may be adapted to generate dynamic security values in cooperation with the removable security device. The acoustic signal received by the token may be modulated using a frequency shift keying modulation scheme using a plurality of coding frequencies to code the acoustical signal where each coding frequency may be an integer multiple of a common base frequency.