As I understand it, cryptosystems based on LWE/Ring-LWE are typically only IND-CPA, and fail to satisfy IND-CCA2. In fact, it appears that chosen ciphertext attacks could allow secret key recovery (!).

What is the best known IND-CCA2 secure encryption algorithm based on (Ring-)LWE? What about key exchange?

  • $\begingroup$ I think that having homomorphic properties precludes the ability to have IND-CCA2 status in general; I wish I had a better reference then this, but I can't seem to find one right now. $\endgroup$
    – Ella Rose
    Jun 14 '17 at 1:12
  • $\begingroup$ @EllaRose I know. I don't need or want homomorphic properties. $\endgroup$
    – Demi
    Jun 14 '17 at 1:16

If you don't mind relying on random oracles, the simplest approach is to apply a generic transformation such as Fujisaki-Okamoto to the (Ring-)LWE based scheme you start from. See for example Peikert's PQCrypto'14 paper for a concrete instantiation, and the TCC 2016 paper of Targhi and Unruh for a proof of security of this type of transform in the quantum random oracle model.

Lattice-based CCA2-secure encryption in the standard model is usually obtained using lattice trapdoors. The state-of-the-art construction is due to Micciancio and Peikert (section 6.3 of this EUROCRYPT 2012 paper).


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