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Title:
Additively Homomorphic IBE from Higher Residuosity
Authors: Michael Clear, Ciaran McGoldrick
Abstract:We present an identity-Based encryption (IBE) scheme that is group homomorphic for addition modulo a large'' (i.e. superpolynomial) integer, the first such group homomorphic IBE. Our first result is the construction of an IBE scheme supporting homomorphic addition modulo a poly-sized prime $e$. Our construction builds upon the IBE scheme of Boneh, LaVigne and Sabin (BLS). BLS relies on a hash function that maps identities to $e$-th residues. However there is no known way to securely instantiate such a function. Our construction extends BLS so that it can use a hash function that can be securely instantiated. We prove our scheme IND-ID-CPA secure under the (slightly modified) $e$-th residuosity assumption in the random oracle model and show that it supports a (modular) additive homomorphism. By using multiple instances of the scheme with distinct primes and leveraging the Chinese Remainder Theorem, we can support homomorphic addition modulo a large’’ (i.e. superpolynomial) integer. We also show that our scheme for e > 2 is anonymous by additionally assuming the hardness of deciding solvability of a special system of multivariate polynomial equations. We provide a justification for this assumption by considering known attacks.
ePrint: https://eprint.iacr.org/2019/062
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