  In this paper, we study the problem of summation evaluation of secrets. The
secrets are distributed over a network of nodes that form a ring graph.
Privacy-preserving iterative protocols for computing the sum of the secrets are
proposed, which are compatible with node join and leave situations. Theoretic
bounds are derived regarding the utility and accuracy, and the proposed
protocols are shown to comply with differential privacy requirements. Based on
utility, accuracy and privacy, we also provide guidance on appropriate
selections of random noise parameters. Additionally, a few numerical examples
that demonstrate their effectiveness are provided.
