Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Efficient physical layer encryption ] Date Submitted: [12 November 2007”] Source: [H.Afifi] Company [MAGNET BEYOND] Address [9 rue Charles Fourrier, Evry, France] Voice:[+33 1 60 76 47 08], FAX: [], E-Mail:[magnet_b@aau.dk] Re: [] Abstract: [A general proposal to implement encryption at the physical layer. The work presented here is adapted to a specific physical layer designed in the MAGNET Beyond IST European project. The idea is highlighted because it could, after adaptation fit into the MBAN architecture] Purpose: [Include encryption in the Working group activities] Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. NOTE: Update all red fields replacing with your information; they are required. This is a manual update in appropriate fields. All Blue fields are informational and are to be deleted. Black stays. After updating delete this box/paragraph. H.Afifi, MAGNET BEYOND

2. Efficient physical layer encryption Afifi, Ahmad and Magnet Beyond WP4 partners H.Afifi, MAGNET BEYOND

3. Outline: • Introduction. • Literature Survey • Our approach. • Example of application • Conclusion. H.Afifi, MAGNET BEYOND

4. 1-1. Introduction Physical layer security can be classified in three categories: • Power approach (power allocation, beamforming) • Channel approach ( information theory) • Code approach (scrambling …..etc) • Information theoretic approach Wherecan the physical layer security be applied ? H.Afifi, MAGNET BEYOND

5. 1-2. Introduction • Ourapproach triggers the physical layer encryption • Key Stream Encryption. • Block cipher is the keystream generator • Why encryption at the physical layer? • For preventing the maximum of attacks or making them more difficult • It is much more difficullt to build lower layer analyser. • Compared to a MAC encryption, we may only miss fragmentation problems • Compared to upper layers encryption (TLS, IPSEC, etc…) we don’t address the same issues • implementing security at hardware level provides manufacturers • with much efficiency and flexibility in terms of implementation design • and technologies. H.Afifi, MAGNET BEYOND

6. 2.Literaturesurvey: • The security on the CDMA systems: • User’s signal is spread using a (Channelization code) and then it is scrambled. • Scrambling code + Channelization code = The built in security. • The built in security relies on the use of LFSR (42 bits) and a long code mask • (42 bits). • This security solution is not sufficient. • [1] enhaces the built in security by using AES in the scrambling process • Good approach but the frame’s size to be encrypted is not defined. • [2] enhaces the built in security by using AES in the interleaving process • The computational complexity becomes a significant problem for the receivers • [3] uses a self synchronisation architecture using a special sync pattern • One lost bit in the sync pattern  synchronisation is lost H.Afifi, MAGNET BEYOND

7. 3-1.Our approach : • We apply the encryption just after the encoding process • OFB (Output Feedback Mode) is used as an encryption mode. • AES takes the role of the encryption cipher • Advantages of using this architecture: • OFB does not propagate the errors: 1 error occured in the • propagation channel produces only 1 error after the decryption • process.( it is not the case with CFB and CBC modes) • OFB does not affect the functionality of the • Encoder/Decoder block. • AES is robust an known enough and can be • implemented in hardware. H.Afifi, MAGNET BEYOND

8. 3-2.Our approach : Application feild: • Our architecture can be applied for High Data Rate (HDR) and Low Data Rate (LDR) devices in wireless and wired communication systems. • implementing this solution in LDR devices is valuable because: 1) Legacy protocols are very heavy to be implemented in these devices. 2) Some kinds of LDR devices don’t have upper layers. 3) LDR devices require minimal security implementation with a low cost. H.Afifi, MAGNET BEYOND

9. Example of application • This example is targetting MAGNET LDR architecture. - MAGNET LDR architecture relies on the use of 802.15.4 MAC layer. - We modify MAGNET physical layer architecture in order to insert the encryption process. - CSMA-CA is the used mechanism to access the medium. - The Key and the IV are registered in the software/hardware interface (some additional feature needed in the architecture. - The framing block is the responsable part of constructing the final frame. • We apply this example on a sensor network in a star topology. H.Afifi, MAGNET BEYOND

10. MAGNET architecture for LDR devices Dotted lines represent our propsal H.Afifi, MAGNET BEYOND

11. To avoid the excessive power consumption, An identification mechanism is defined. • Each node has a Physical Layer Security Association Identifiers(PHSAid) • This mechanism gives the receiver the possibility to identify the sender . H.Afifi, MAGNET BEYOND

12. Conclusion • The security solution is implemented in hardware • Our proposal hides whole the MAC frame • ==(location privacy). • It does not degrade the communication performances • (encoding/encryption operations are independent of each • other. • Some kinds of attacks are prevented (M-I-M, Sybil , • node replication ..) and some others are becoming much • more dificult (DoS, plaintext attack ). • A kind of synchronisation between the encryption/ • decryption process is acheived. H.Afifi, MAGNET BEYOND

13. References [1] Jian Ren, Tongtong Li “CDMA Physical Layer Built-in Security Enhancement” 2003 IEEE. [2] Qi Ling, Tongtong Li and Jian Ren “Physical Layer Built-in Security Enhancement of DS-CDMA Systems Using Secure Block Interleaving” This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE GLOBECOM 2005 proceedings. [3] Howard M. Heys “Analysis of theStatistical Cipher Feedback Mode of Block Ciphers” IEEE transactions on computers, vol. 52, NO. 1, 2003. [4] MAGNET Deliverable : D3.2.1, “Prototype specification for the FM-UWB and MC-SS RA schemes”. June 30th 2006. [5] K. Daniel Wong, “Physical Layer Considerations for Wireless Sensor Networks”. Proceedings of the 2004 IEEE International Conference on Networhng, Sensing 8. Control Taipei. Taiwan, March 21-23, 3004. H.Afifi, MAGNET BEYOND