> It wasn't until the late 1990s (as far as I can tell) that anyone made the leap from covert channels --- which have cooperating agents on either end of the ch

> It wasn't until the late 1990s (as far as I can tell) that anyone made the leap from covert channels --- which have cooperating agents on either end of the channel --- to side channels, in which the transmitter is unwitting. In the public domain, anyway. Presumably NSA folks had thought about this in the context of TEMPEST-style attacks?