When Someone asks me how I am, I try to make my answer as specific as possible. I'm not the type to toss off a casual, "I'm fine." I take care to express my exact condition. And thanks to my creative flair, I can choose from a number of options:
If I'm in a self-protective mood, a simple "guardedly well" often does the job. I find also "tentatively keen" doesn't give too much away. Of course, if there is the least bit of doubt, I simply rely on my old standby, the ever cautious, "I'm fairly well, comparatively speaking." That works nicely, especially if I feel I genuinely have something to hide.