Counterfactual communication is a communication without particles in the transmission channel.
Since there are no particles to observe, it apparently cryptographically secure because Eve has nothing to eavesdrop on. However, the issue is highly controversial. It will be presented (and hopefully debated) in Poster 17 (see abstract) and in a meeting at Room 202 Tuesday 10:00.
The solution(s) will be presented and defended in a second meeting at Room 202, Thursday 16:00.