  We consider a group of m+1 trusted nodes that aim to create a shared secret
key K over a network in the presence of a passive eavesdropper, Eve. We assume
a linear non-coherent network coding broadcast channel (over a finite field
F_q) from one of the honest nodes (i.e., Alice) to the rest of them including
Eve. All of the trusted nodes can also discuss over a cost-free public channel
which is also overheard by Eve.
  For this setup, we propose upper and lower bounds for the secret key
generation capacity assuming that the field size q is very large. For the case
of two trusted terminals (m = 1) our upper and lower bounds match and we have
complete characterization for the secrecy capacity in the large field size
regime.
