Paper 2010/178

Identity Based Online/Offline Encryption Scheme

Sharmila Deva Selvi S, Sree Vivek S, and Pandu Rangan C


Consider the situation where a low power device with limited computational power has to perform cryptographic operation in order to do secure communication to the base station where the computational power is not limited. The most obvious way is to split each and every cryptographic operations into resource consuming, heavy operations (which are performed when the device is idle) and the fast light weight operations (which are executed on the fly). This concept is called online/offline cryptography. In this paper, we show the security weakness of an identity based online offline encryption scheme proposed in ACNS 09 by Liu et al. \cite{LiuZ09}. The scheme in \cite{LiuZ09} is the first identity based online offline encryption scheme in the random oracle model, in which the message and recipient are not known during the offline phase. We show that this scheme is not CCA secure. We show the weakness in the security proof of CCA secure online/offline encryption system proposed by Chow et al. in \cite{Chow10}. We propose a new provably secure identity based online offline encryption scheme in which the message and receiver are not known during the offline phase. Since all the CCA secure identity based online/offline encryption schemes are shown to have weakness, ours is the first provably secure scheme with the aforementioned properties.

Available format(s)
Public-key cryptography
Publication info
Published elsewhere. Unknown where it was published
Identity BasedEncryptionOnlineOfflineCryptanalysis
Contact author(s)
sharmioshin @ gmail com
ssreevivek @ gmail com
sharmioshins @ gmail com
2010-07-30: last of 3 revisions
2010-04-04: received
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      author = {Sharmila Deva Selvi S and Sree Vivek S and Pandu Rangan C},
      title = {Identity Based Online/Offline Encryption Scheme},
      howpublished = {Cryptology ePrint Archive, Paper 2010/178},
      year = {2010},
      note = {\url{}},
      url = {}
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