  We consider a pair-wise independent network where every pair of terminals in
the network observes a common pair-wise source that is independent of all the
sources accessible to the other pairs. We propose a method for secret key
agreement in such a network that is based on well-established point-to-point
techniques and repeated application of the one-time pad. Three specific
problems are investigated. 1) Each terminal's observations are correlated only
with the observations of a central terminal. All these terminals wish to
generate a common secret key. 2) In a pair-wise independent network, two
designated terminals wish to generate a secret key with the help of other
terminals. 3) All the terminals in a pair-wise independent network wish to
generate a common secret key. A separate protocol for each of these problems is
proposed. Furthermore, we show that the protocols for the first two problems
are optimal and the protocol for the third problem is efficient, in terms of
the resulting secret key rates.
