We present an implementation of asynchronous causally ordered unicast that requires linear space for message size, which is a significant improvement compared to the best existing algorithms which require quadratic space in the worst case. This algorithm is a modification of the Raynal-Shiper-Toueg algorithm and broadcasts a small control message, defined here as a minicast, to augment the unicast message to preserve causal ordering. The smaller message size is at the cost of additional traffic on the network. With the addition of cryptography in the form of digital signatures, this algorithm can be made tolerant to byzantine failures. For existing versions of causal unicast, byzantine tolerance has previously only been possible with the addition of bounded latency.