We consider the situation in which digital data is to be reliably transmitted over a discrete, memoryless channel (DMC) that is subjected to a wire‐tap at the receiver. We assume that the wire‐tapper views the channel output via a second DMC. Encoding by the transmitter and decoding by the receiver are permitted. However, the code books used in these operations are assumed to be known by the wire‐tapper. The designer attempts to build the encoder‐decoder in such a way as to maximize the transmission rate R, and the equivocation d of the data as seen by the wire‐tapper. In this paper, we find the trade‐off curve between R and d, assuming essentially perfect (“error‐free”) transmission. In particular, if d is equal to H s, the entropy of the data source, then we consider that the transmission is accomplished in perfect secrecy. Our results imply that there exists a C8 > 0, such that reliable transmission at rates up to CS is possible in approximately perfect secrecy.

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