Subject: Which is the difference between front, group, signal and energy velocities?

I have been reading some papers about quantum tunneling and 
evanescent modes, in which is pointed out that some signals can
travel faster than light. This looks to violate Special 
Relativity and Relativistic Causality, but in fact, it does not!
because of the difference between front, group, and other
velocities. So, I'm puzzled. What is that difference?! And How
a single photom have different velocities?

Re: Which is the difference between front, group, signal and energy velocities?