PKE Key-Switching documentation

Github Source: This folder contains the header files of the key-switching methods present in Open-FHE.

The documentation is based on Revisiting Homomorphic Encryption Schemes for Finite Fields

Page Contents

Intuition
Key-Switching Class Inheritance
File Listings

Intuition 

Let $c_t$ be a ciphertext $c_t = (c_0, c_1) \in \mathbb{R}_Q^2$ , which can be decrypted with $s_A$ .

Through key-switching, we create a new ciphertext, $c_t'$ such that $c_t' = (c_0', c_1') \in \mathbb{R}_Q^2$ , which contains the same message as $c_t$ , but can be decrypted by a different secret key $s_B$ .

Key switching

This feature is needed to compute automorphisms(rotations) of ciphertexts, or to relinearize ciphertexts

Key-Switching Class Inheritance 

File Listings 

Key-Switch Base (keyswitch-base.h)

Base class for key switching algorithms.

Key-Switch RNS (keyswitch-rns.h)

Abstract interface class for key switching algorithms in RNS

Key-Switch BV (keyswitch-bv.h)

Implements BV scheme from Fully Homomorphic Encryption from Ring-LWE and Security for Key Dependent Messages (BV Scheme)
Requires the computation of a quadratic number of NTTs.
See the Appendix of https://eprint.iacr.org/2021/204 for more detailed description of the RNS variant.

Key-switch Hybrid (keyswitch-hybrid.h)

Hybrid key switching method first introduced in https://eprint.iacr.org/2012/099.pdf

RNS version was introduced in https://eprint.iacr.org/2019/688.

See the Appendix of https://eprint.iacr.org/2021/204 for more detailed description.

PKE Key-Switching documentation

Intuition

Key-Switching Class Inheritance

File Listings

Intuition 

Key-Switching Class Inheritance 

File Listings 