Abstract
In this paper we want to enhance the powerful of HMAC function (Key-Hashed Message Authentication) to he more resistant against the Exhaustive search attack and Birthday Attack hy inventing d-HAMC function (dynamic HMAC function). To achieve our purpose we use dynamic values of ipad and opad The values of ipad and opad are calculated in dynamic way instead of having fixed strings. The calculation of the values of ipad and opad will depend on the input parameters for HAMC and the input message.