If a smart card is capable of presenting trusted output to the customer (for example, through an integral display) and the customer can reply with one bit of trusted input (such as removing the smart card from the reader) then the customer and smart card can achieve a trusted input channel. The customer communicates to the smart card via an untrusted input channel and the smart card then echoes back the input message through the trusted output channel. If the customer disagrees with the message displayed by the smart card, the customer communicates this via the single bit of trusted input.