  A subset of a set of terminals that observe correlated signals seek to
compute a given function of the signals using public communication. It is
required that the value of the function be kept secret from an eavesdropper
with access to the communication. We show that the function is securely
computable if and only if its entropy is less than the "aided secret key"
capacity of an associated secrecy generation model, for which a single-letter
characterization is provided.
