DRKH: A Power Efficient Encryption Protocol for Wireless Devices

1. DRKH: A Power Efficient Encryption Protocol for Wireless Devices El Shibani Omar Hamdan Alzahrani

2. DRKH • Dynamic Re-keying Key Hopping is a simple lightweight security protocol that’s suitable for solar and battery powered devices. It implements RC4 in a way that doesn’t require intensive computations to preserve power also it insures high security in addition to low execution cost. • It uses a Hash function to generate session keys. Baraka, Eissa, Fayek, and Kholaif. “DRKH: A Power Efficient Encryption Protocol for Wireless Devices” Local Computer Networks, Sydney, NSW. IEEE. 2005. DRKH/ Hamdan and El Shibani

3. SharedParameters • Secret Keys [1..4] • Authentication Key • Hopping Sequence [1..4] • Broadcast key • Session counter • Initialization Vector [1..4] • Nonce DRKH/ Hamdan and El Shibani

4. Important Notions • Session Duration: It represents the start and the end of a session. • Indicates session expiration. • The four session keys are no longer valid and four different ones have to be generated. DRKH/ Hamdan and El Shibani

5. Important Notions (con’t) • Session Keys: Session Keys are the keys used to generate the cipher stream that’s used in an XOR operation with the plaintext to generate the cipher text. • Generated at the beginning of each new session. • A hash function is used to generate them using the four secret keys and the session counter. DRKH/ Hamdan and El Shibani

6. Link-Layer Authentication • STA initiate a request AP. • AP challenge message E(X, N1) STA. • STA encrypted message E(X, (N1, N2, SSID)) AP. • Access point decrypts the message and check the validity of nonce 1 (N1) and Service Set Identifier (SSID) if they match what access point has then it’s considered that station authenticated. DRKH/ Hamdan and El Shibani

7. Link-Layer Authentication (con’t) • AP E(X, N2, Hopping sequence, N3, Broadcast key) STA • STA after receiving the message it decrypts it and verify N2. After verification is done it’s only now that AP is considered authenticated by the STA. • STA E( positive ACK) AP DRKH/ Hamdan and El Shibani

8. The Road to Session Keys Generation • The first step is to generate the four secret keys. • Mixing them with the session counter. • Using a strong one-way hash function such as SHA-1 (Secure Hash Algorithm) to generate the four session keys. DRKH/ Hamdan and El Shibani

9. The Encryption and the Decryption of a Message • Choose the session key based on the hopping sequence. • The IV corresponding to the chosen session key is then incremented by one and mixed with the corresponding session key using a non-linear lookup based-table substitution. • The output form the previous step is then used to reinitialize RC4 state (Not KSA). • Then station runs the initialized RC4-PRNA(pseudo-random generation algorithm) to produce cipher stream. • The final step is to XOR the resulted cipher stream with the plaintext to generate the cipher text. DRKH/ Hamdan and El Shibani

10. Conclusion • In this paper a lightweight wireless security protocol, DRKH, was presented. • DRKH is suitable for solar and battery powerd devices. • The focus was mostly on the steps to generate the session keys using a one-way hash function. • These session keys are used for data encryption and decryption in DRKH. DRKH/ Hamdan and El Shibani

11. References • [1] Baraka, Eissa, Fayek, and Kholaif. “DRKH: A Power Efficient Encryption Protocol for Wireless Devices” Local Computer Networks, Sydney, NSW. IEEE. 2005. • [2] Jones, P. www.ietf.org. The Internet Engineering Task Force (IETF). September 2001. Web. 16 April 2011. • [3] Wade, and Lawrence Washington. Introduction to Cryptography with Coding Theory. New Jersey: Pearson Education, 2006. print. DRKH/ Hamdan and El Shibani