Protocols that provide authentication and key distribution are mainly based on symmetric and asymmetric ciphers. In recent years, some approaches have been introduced that are based on strong one-way hash functions, and further enhancements to these approaches are given in this paper. The lightweight protocols that are presented in this paper are suitable for implementation with simple logic. They enable early recognition of attacks and make distributed session key generation possible. They are intended for use in environments with limited processing capabilities, where relatively short messages are being exchanged, e.g., agents environments.