Abstract: Identity authentication and key agreement schemes play significant role in ad hoc networks. In this study, a new identity authentication scheme relies on the threshold group signature is introduced. Compared with the current schemes it is secure, efficient and adaptable to a multi-hop feature of ad hoc networks. In addition, a new key agreement scheme based on the threshold cryptography using the Lagrange interpolation theorem is suggested, its efficiency and security are examined and is claimed to be more efficient than the existing schemes.