  We consider the secret key agreement problem under the multiterminal source
model proposed by Csisz\'ar and Narayan. A single-letter characterization of
the secrecy capacity is desired but remains unknown except in the extreme case
with unlimited public discussion and without wiretapper's side information.
Taking the problem to the opposite extreme by requiring the public discussion
rate to be zero asymptotically, we obtain the desired characterization under
surprisingly general setting with wiretapper's side information, silent users,
trusted and untrusted helpers. An immediate consequence of the result is that
the capacity with nearly no discussion is the same as the capacity with no
discussion, resolving a previous conjecture in the affirmative. The idea of the
proof is to characterize the capacity in the special case with neither
wiretapper's side information nor untrusted helpers using a multivariate
extension of G\'acs-K\"orner common information, and then extend the result to
the general setting by a change of scenario that turns untrusted helpers into
trusted helpers. We further show how to evaluate the capacity explicitly for
finite linear sources and discuss how the current result can be extended to
improve and unify existing bounds on the capacity for strictly positive
discussion rates.
