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

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 /3/2016DRKH/ Hamdan and El Shibani 2

Shared Parameters Secret Keys [1..4] Authentication Key Hopping Sequence [1..4] Broadcast key Session counter Initialization Vector [1..4] Nonce 6/3/2016DRKH/ Hamdan and El Shibani 3

Important Notions Session Duration: It represents the start and the end of a session. 1. Indicates session expiration. 2. The four session keys are no longer valid and four different ones have to be generated. 6/3/2016DRKH/ Hamdan and El Shibani 4

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. 1. Generated at the beginning of each new session. 2. A hash function is used to generate them using the four secret keys and the session counter. 6/3/2016DRKH/ Hamdan and El Shibani 5

Link-Layer Authentication 1. STA initiate a request AP. 2. AP challenge message E(X, N1) STA. 3. STA encrypted message E(X, (N1, N2, SSID)) AP. 4. 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. 6/3/2016DRKH/ Hamdan and El Shibani 6

Link-Layer Authentication (con’t) 5. AP E(X, N2, Hopping sequence, N3, Broadcast key) STA 6. 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. 7. STA E( positive ACK) AP 6/3/2016DRKH/ Hamdan and El Shibani 7

The Road to Session Keys Generation 1. The first step is to generate the four secret keys. 2. Mixing them with the session counter. 3. Using a strong one-way hash function such as SHA-1 (Secure Hash Algorithm) to generate the four session keys. 6/3/2016DRKH/ Hamdan and El Shibani 8

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. 6/3/2016DRKH/ Hamdan and El Shibani 9

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. 6/3/2016DRKH/ Hamdan and El Shibani 10

References [1] Baraka, Eissa, Fayek, and Kholaif. “DRKH: A Power Efficient Encryption Protocol for Wireless Devices” Local Computer Networks, Sydney, NSW. IEEE [2] Jones, P. The Internet Engineering Task Force (IETF). September Web. 16 April [3] Wade, and Lawrence Washington. Introduction to Cryptography with Coding Theory. New Jersey: Pearson Education, print. 6/3/2016DRKH/ Hamdan and El Shibani 11