### Downgradable Identity-based Encryption and Applications

Olivier Blazy, Paul Germouty, and Duong Hieu Phan

##### Abstract

In Identity-based cryptography, in order to generalize one receiver encryption to multi-receiver encryption, wildcards were introduced: WIBE enables wildcard in receivers' pattern and Wicked-IBE allows one to generate a key for identities with wildcard. However, the use of wildcard makes the construction of WIBE, Wicked-IBE more complicated and significantly less efficient than the underlying IBE. The main reason is that the conventional identity's binary alphabet is extended to a ternary alphabet $\{0,1,*\}$ and the wildcard $*$ is always treated in a convoluted way in encryption or in key generation. In this paper, we show that when dealing with multi-receiver setting, wildcard is not necessary. We introduce a new downgradable property for IBE scheme and show that any IBE with this property, called DIBE, can be efficiently transformed into WIBE or Wicked-IBE. While WIBE and Wicked-IBE have been used to construct Broadcast encryption, we go a step further by employing DIBE to construct Attribute-based Encryption of which the access policy is expressed as a boolean formula in the disjunctive normal form.

Available format(s)
Category
Cryptographic protocols
Publication info
Published elsewhere. MINOR revision.CT-RSA 2019
Keywords
Identity-Based EncryptionAttribute-Based Encryption
Contact author(s)
olivier blazy @ unilim fr
History
Short URL
https://ia.cr/2018/1176

CC BY

BibTeX

@misc{cryptoeprint:2018/1176,
author = {Olivier Blazy and Paul Germouty and Duong Hieu Phan},
title = {Downgradable Identity-based Encryption and Applications},
howpublished = {Cryptology ePrint Archive, Paper 2018/1176},
year = {2018},
note = {\url{https://eprint.iacr.org/2018/1176}},
url = {https://eprint.iacr.org/2018/1176}
}

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