331 modified leighton micali scheme in the mls scheme

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3.3.1. Modified Leighton-Micali Scheme In the MLS scheme the KDC chooses a master secret K . A node A is inducted into the network by providing the entity with a secret K A = h ( K, A ) (13) In order to establish a secret with B (which is issued a secret K B = h ( K, B )) the node inducted later into the network is provided with a public value P AB = h ( K A , B ) h ( K B , A ) (14) For example, if B was inducted after A , only B has access to the public value P AB . The shared secret K AB is computed as K AB = h ( K A , B ) by A h ( K B , A ) P AB by B (15) Thus, both A and B can compute a common secret K AB = h ( K A , B ) with- out involvement of the KDC. For this purpose, every node is provided as many public vales as the number of nodes inducted into the network earlier. The first node receives only one secret and no public values. The second node receives one secret and one public value. The millionth inducted node receives one secret and 999 , 999 public values. On an average, every node will need to store N/ 2 public values. The network can scale to the extent permitted by storage. It is also intuitively appealing that newly inducted entities will need more storage than older entities. With the current rate of advances in storage capabilities of mobile devices entities inducted in the year 2010 will obviously be able to tolerate more storage than an entity inducted in 2009. The MLS scheme is a modification of an alternative to Kerberos pro- posed by Leighton and Micali, 14 where an online KDC computes public val- ues on demand. Furthermore, unlike the original scheme where the pairwise secret between A and B is different depending on who ( A or B ) initiates the exchange, in the MLS scheme 13 a fixed rule determines how K AB is computed, irrespective of who initiated the exchange. Copyright © 2010. World Scientific Publishing Company. All rights reserved. May not be reproduced in any form without permission from the publisher, except fair uses permitted under U.S. or applicable copyright law. EBSCO Publishing : eBook Collection (EBSCOhost) - printed on 2/16/2016 3:46 AM via CGC-GROUP OF COLLEGES (GHARUAN) AN: 340572 ; Beyah, Raheem, Corbett, Cherita, McNair, Janise.; Security in Ad Hoc and Sensor Networks Account: ns224671
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Key Distribution 47 4. The Cost of Security Associations The price paid for employing cryptographic security associations is the over- head mandated for this purpose. 4.1. Overhead The overhead for using cryptographic SAs can be broadly classified into computational overhead (for computing and verifying cryptographic SAs), bandwidth overhead (both in-network and out-of network overhead), and storage overhead. 4.1.1. Computational Overhead One-to-one SAs: For certificate based public key schemes the computa- tions required for a node A to compute a shared secret K AB are 1) verifi- cation of public key certificate of B by verifying the signature of the CA; 2) one public key encryption to convey a secret to B ; and 3) one public key decryption to decrypt a secret conveyed by B . For an n -secure Blom’s KPS, computation of K AB will require A to perform 2 n finite-field operations.
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