Reading though these posts reminds me of the time I was at a family gathering and everybody was talking about how proud they were of my step-brother's son who was then a 12-year-old black belt. He mentioned to me that he had learned to defend against knife attacks. I took him aside and told him to never mess with a guy armed with a knife. Run, hide, grab something and throw it, whatever, but understand that fighting back is the absolute last resort, and that survival is the best you can hope for. Even if you are a five foot tall 12-year-old blackbelt!
Needless to say he didn't believe me. I mean after all he had the black belt right? And who was I? His middle-aged step-uncle who does some kinda MA that doesn't even have belts! So to make the point, I grabbed a harmless kitchen spatula and asked him if he thought he could defend against it if it were a knife. He said sure. So I charged him, knocked him to the floor and "stabbed" him with the spatula about twenty times. Boy, did his eyes get big. My wife went all ballistic on me for "beating up on a little kid". But my step brother, the boy's father, understood perfectly ...and so did the kid. Maybe the lesson will keep him from doing something stupid down the road.
As to "Dolev", I understand you want a reasonable and reliable empty-handed knife-defense that you can count on. The bad news (as has already been stated) is that such a defense doesn't exist. There are some approaches that are just unrealistic and really stupid, and others that are better. Some of each have been discussed here. The better ones are very simple, direct, powerful and delivered with focused, violent even desperate aggression. Improvised weapons can help even the odds, if you can get your hands on them in time. But a lot of attacks happen before you are even aware that there's a threat. Which technique will protect you when you suddenly realize that you have just been stabbed from behind and didn't even know it until you felt that sharp pain like a hard punch, felt the warm sticky blood on your fingers as you grab the spot, and caught a glimpse of the other guy walking away? Food for thought.