Secure summation is one of the most applicable functions of secure multiparty computation (MPC) in which a group of users securely computes the summation value of their private inputs. The current solutions to this problem are basically on adding a random number to private inputs or splitting the inputs among users which need secure channel among members. Moreover, to be resistant against collusion of n - 2 players, they impose high communication cost. In this paper, we propose three cryptography-based protocols for secure sum that do not need secure channel and are secure against collusion of n - 2 players. Also, the communication cost of the proposed protocols is of complexity O(n). Based on the privacy requirements, the proposed protocols can provide the final result privacy as well as the private input privacy.