if you're just using compress and you make that known

Yes, this is worth pointing out; the main idea is to keep the opponent from knowing the format. Increasing the entropy via compressions is good in its own right since it makes the encoding more complex and provides more stumbling blocks. Cypher chaining seems to be even better for confounding opponents, but I'll let someone else commment on that. Paul E. Baclace peb@procase.com