A flexible and polynomial framework for integer arithmetic in CKKS

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This repository contains an OpenFHE-based project that implements a computational device that handles power-of-two exact arithmetic, up to 256-bits.

The reference paper for this work is A flexible and polynomial framework for integer arithmetic in CKKS.

❗ Keep in mind!
This repo is still WIP, so feel free to report any issue! ^^

Fresh start

One of the key ideas behind this work is simplicity. It can indeed be used by simply installing a custom OpenFHE fork and by compiling the CMake project.

We require a custom fork of OpenFHE (that is updated to v1.5.0 and it includes the StC-first bootstrapping), this allows to use the two functions EvalChebyshevSeriesPSBatchRepeated and EvalBootstrapStCFirstBits. The first generalizes the functionality to evaluate a Chebyshev polynomial over a ciphertext to evaluate $n$ Chebyshev polynomials, one for each slot of the ciphertext. The second allows to evaluate a cleaning bootstrapping operation à la [BCKS24].

1. Install the repeated_poly_and_stcboot branch from this custom fork of OpenFHE

git clone --branch repeated_poly_and_stcboot --single-branch https://github.com/lorenzorovida/openfhe-development-chebyshevSIMD
cd openfhe-development-chebyshevSIMD
mkdir build
cmake ..
sudo make install

2. Now, navigate to your desired folder and install this repository

git clone https://github.com/lorenzorovida/flexible-integer-arithmetic-ckks
cd flexible-integer-arithmetic-ckks
mkdir build

The CMakeLists.txt must point to the custom version of OpenFHE. Be sure to replace all the instances of /Users/myuser/openfhe-development-chebyshevSIMD/build in the CMakeLists.txt file to your custom build folder! After that, build the repository:

cmake ..
make

Important

The compilation will fail if you are using the original version of OpenFHE, use the fork!

3. Finally, you can test if everything works by running

./FlexibleIntsCKKS --test

Custom parameters

There are three parameters that can be passed to ./FlexibleIntsCKKS

1. --ring <size>

Sets the (logarithm of the) ring size. <size> must be an integer in (12, 13, 14, 15, 16). Example:

./FlexibleIntsCKKS --ring 16

2. --bits <bits>

Sets the word size (number of bits per word). Only the following values are supported: 8, 16, 32, 64, 128, 256. If an unsupported value is provided, the program will display an error. Example:

./FlexibleIntsCKKS --bits 64

3. --verbose <value>

Sets the verbosity level of program output. <value> must be either 0, 1 or 2. Higher numbers mean more detailed output. Example:

./FlexibleIntsCKKS --verbose 2

4. --input

Sets the program in input mode, i.e., the program will ask you to set the number of desired bits and to manually insert the values you want to compute operations on.

Examples of usage

Toy parameters

You can test 64-bits operation, in the $N=2^{12}$ ring, with the following code:

./FlexibleIntsCKKS --ring 12 --bits 64

This allows to test the code in a unsecure environment, useful if playing around with the code.

More secure parameters

You can test 64-bits operation, in the $N=2^{16}$ ring, with the following code:

./FlexibleIntsCKKS --ring 16 --bits 64

Input mode

You can use the program and manually insert some values to operate on

./FlexibleIntsCKKS --ring 12 --input