Abstract:
In this paper, we present an identity-based encryption scheme from codes with efficient key
revocation. Recently, in Crypto 2017, Gaborit et al. proposed a first identity-based encryption scheme
from codes with rank metric, called RankIBE. To extract the decryption key from any public identity, they
constructed a trapdoor function which relies on RankSign, a signature scheme proposed by Gaborit et al.
in PQCrypto 2014. We adopt the same trapdoor function to add efficient key revocation functionality in
the RankIBE scheme. Our revocable IBE scheme from codes with rank metric makes use of a binary tree
data structure to reduce the amount of work in terms of key updates for the key authority. The total
size of key updates requires logarithmic complexity in the maximum number of users and linear in the
number of revoked users. We prove that our revocable IBE scheme is selective-ID secure in the random
oracle model, under the hardness of three problems: the Rank Syndrome Decoding (RSD) problem, the
Augmented Low Rank Parity Check Code (LRPC+) problem, and the Rank Support Learning (RSL) problem.
