Question about the Clipper Chip

I have heard that the Clipper Chip is only supposed to be used for voice applications. Does anyone know if the inputs and outputs of the Clipper Chip digital or analog? That is does the clipper chip input/output an analog signal with some sort of internal analog to digital converter or does have purely digital inputs and outputs? The reason I ask is, if the chip does analog IO, then it would be possible for the chip to be designed to deliberately leak its own key disguised as a measurement error in the low bits of the analog to digital/analog conversion.