Abstract: Pervasive computing is a new technology which will be integrated into all the objects that interact with peoples, to enhancement and make people's routine lives easier through making the process of those objects interactive automatically to anything and everything in every place and at any moment of time in their environment without human intervention as possible. Security is very important element in pervasive computing environment to protect data that is transferred between devices connected with each other via (Wi-Fi or Bluetooth …etc.). This papers proposed a new secure method called HDOTP which is determine on Diffie-Hellman key exchanging to exchange and establish secret key and use this secure key as an initial key in One-Time pad algorithm with new algorithm for steam key generator to generate a random key and compared it with RSA and ElGamal according to parameter performance (runtime, memory usage, avalanche Effect, throughput) and concluded that HDOTP is more efficient than RSA and ElGamal.

Keywords: Pervasive computing environment, cryptography, RSA, ElGamal, Diffie-Hellman Key Exchange, One Time Pad, key stream.