A method of encrypting a plain text message that is m characters in length is described. Means for Solution: The test reagent for the analyte comprises at least a Solution A which is a buffer solution having an electric conductivity of not less than 30 mscm; and a Solution B having an electric conductivity of not more than 6. Preferably, the modulation signal fluctuates period of the oscillation signal sequentially. Polarization axes of the display-side polarizing plate and the first glasses-side polarizing plate are orthogonal. , for detecting the codes, which is connected to the electronic circuit.