An Efficient and Provable Secret Shared Key Computation for Cryptographic Protocol Across Insecure Channel Data exchange over public network requires for the most part an important security mechanism enabling to both sender and receiver the property that they can mutual authenticate using different identification parameters playing the vital role of secret shared key computation. Based on the decisional Diffie-Hellman assumptions, this paper presents a cryptographic calculation of the shared secret key enabling mutual authentication and confidentiality services over public, insecure networks. This protocol is efficient than “classical” Diffe-Hellman key exchange which provides no authentication at all and suffer from man-in-the-middle attack. To attain this, we first model the scheme with mathematical concept for exponential calculation using entity parameters and finally we simulate the work by Scyther tool to verify the provability of the sameness ‘shared secret value. With the standards cryptographic assumptions, the simulation result reveals that the protocol is practical and provably-secure. Thus, the proposed cryptographic protocol is awfully, straightforward, valuable, and resilient to know attacks.