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 thats suitable for
  solar and battery powered devices. It implements
  RC4 in a way that doesnt 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.

3
Shared Parameters

• Secret Keys 1..4
• Authentication Key
• Hopping Sequence 1..4
• Broadcast key
• Session counter
• Initialization Vector 1..4
• Nonce

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• The four session keys are no longer valid and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.

5
Important Notions (cont)

• Session Keys Session Keys are the keys used to
  generate the cipher stream thats 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.

6
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 its considered that station
   authenticated.

7
Link-Layer Authentication (cont)

1. AP E(X, N2, Hopping sequence, N3, Broadcast key)
   STA
2. STA after receiving the message it decrypts it
   and verify N2. After verification is done its
   only now that AP is considered authenticated by
   the STA.
3. STA E( positive ACK) AP

8
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.

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.

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.

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.