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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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36 M. Ramkumar K L i A should remain A ’s secret at least till time T i . The value K A L is the commitment to the hash chain (analogous to a public key). The KDC or CA issues certificates of the form A, K L A , , T 1 indicating identity of the node, and the parameters of its hash chain. To authenticate a message M sent before time T j = T 1 + ( j 1)∆, A employs the value K L j A from its TESLA chain to compute (and append) the HMAC M A = h ( M, K L j A ). The value K L j A is made public by A after time T j . Any node with access to the certified commitment of the sender, receiving the message M with the appended TESLA HMAC before time T j (when K L j A was a secret), can verify the message after it gains access to the value K L j A (after time T j when the source makes the value public). TESLA based authentication is 1) delay sensitive as verifiers should receive authenticated packets before some time T j ; and 2) does not facilitate in- stantaneous verification as verifiers have to wait until the secret is made public. 3.1.2. One-Time Signatures (OTS) In one-time signature (OTS) schemes 3 the secret key is used as the start- ing point for many hash function evaluations. A sequence of intermediate results are determined by the message M to be signed. The intermediate results are presented along with the message as the signature. Any verifier can compute the commitment (public key) using the intermediate results (signature) and the message, and thus verify the signature. In the OTS scheme by Bleichenbacher and Maurer 4 to sign a message M , or equivalently, a b -bit hash M of the message M (or M = h ( M )), l “primary” hash chains of length k and l s secondary hash chains of length k s are used, where l log 2 k = b, and kl < k l s s . (1) As an example, for b = 80 ( M is a 80-bit value) we can choose l = 10 primary chains of length k = 2 8 = 256 and l s = 2 secondary chains of length k s = 51. Note that kl = 2560 < k l s s = 51 2 = 2601. To generate an OTS key pair, a node A chooses a private key r o . The head values of the l + l s hash chains are derived from a private key r o as P 0 i = h ( r o , i, 1) , 1 i l and S 0 i = h ( r o , i, 2) for 1 i l s respectively. The tail values of the primary chains are P k i , 1 i l (obtained by repeatedly hashing each P 0 i k times). Similarly S k s i for 1 i l s (obtained by repeatedly hashing each S 0 i k s times) are the tail values of the secondary 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.
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