OpenFHE.jl

OpenFHE.jl is a Julia wrapper package for OpenFHE, a C++ library for fully homomorphic encryption. The C++ functionality is exposed in native Julia via the CxxWrap.jl package, using OpenFHE-julia as its backend.

Note: This package is work in progress and not all capabilities of OpenFHE have been translated to Julia yet. Community contributions are very welcome!

If you have not yet installed Julia, please follow the instructions for your operating system. OpenFHE.jl works with Julia v1.8 and later on Linux and macOS platforms, and with Julia v1.9 or later on Windows platforms.

Since OpenFHE.jl is a registered Julia package, you can install it by executing the following commands in the Julia REPL:

julia> import Pkg; Pkg.add("OpenFHE")

Internally, OpenFHE.jl relies on OpenFHE-julia to provide bindings for the C++ library OpenFHE. Precompiled binares for OpenFHE-julia and OpenFHE are automatically for your platform when you install OpenFHE.jl, thus there is no need to compile anything manually.

The easiest way to get started is to run one of the examples from the examples directory by includeing them in Julia, e.g.,

julia> using OpenFHE

julia> include(joinpath(pkgdir(OpenFHE), "examples", "simple_real_numbers.jl"))
CKKS scheme is using ring dimension 16384

Input x1: (0.25, 0.5, 0.75, 1, 2, 3, 4, 5,  ... ); Estimated precision: 50 bits

Input x2: (5, 4, 3, 2, 1, 0.75, 0.5, 0.25,  ... ); Estimated precision: 50 bits


Results of homomorphic computations:
x1 = (0.25, 0.5, 0.75, 1, 2, 3, 4, 5,  ... ); Estimated precision: 43 bits
Estimated precision in bits: 43.0
x1 + x2 = (5.25, 4.5, 3.75, 3, 3, 3.75, 4.5, 5.25,  ... ); Estimated precision: 43 bits
Estimated precision in bits: 43.0
x1 - x2 = (-4.75, -3.5, -2.25, -1, 1, 2.25, 3.5, 4.75,  ... ); Estimated precision: 43 bits

4 * x1 = (1, 2, 3, 4, 8, 12, 16, 20,  ... ); Estimated precision: 41 bits

x1 * x2 = (1.25, 2, 2.25, 2, 2, 2.25, 2, 1.25,  ... ); Estimated precision: 41 bits


In rotations, very small outputs (~10^-10 here) correspond to 0's:
x1 rotate by 1 = (0.5, 0.75, 1, 2, 3, 4, 5, 0.25,  ... ); Estimated precision: 43 bits

x1 rotate by -2 = (4, 5, 0.25, 0.5, 0.75, 1, 2, 3,  ... ); Estimated precision: 43 bits

OpenFHE is a memory-optimized C++ library, but these optimizations can cause memory issues when transitioning to Julia.

In OpenFHE, large objects like Ciphertext, Plaintext, and CryptoContext are managed using std::shared_ptr. These objects are not freed until all associated std::shared_ptrs are destroyed. Since the Julia objects that hold a reference to these shared pointers are relatively small, Julia's garbage collector does not always free them automatically, as they are not considered a high priority for garbage collection. This is because Julia's garbage collector primarily focuses on "young" objects during its incremental collections, leaving some std::shared_ptrs in memory even when they are no longer in use. This may result in a significant increase in memory consumption over time, as a single Ciphertext object can occupy over 60 MB. Consequently, complex operations may lead to gigabytes of memory being occupied without being freed until the Julia session is terminated. One possible solution is to manually trigger Julia's garbage collector to perform a full collection, which will also clean up these "small" objects:

GC.gc()

Additionally, OpenFHE optimizes memory usage in C++ by storing evaluation keys and CryptoContexts in static objects. These objects, being quite large, remain in memory until the Julia REPL is closed. To release them while the REPL is still running, you can execute the following functions:

ClearEvalMultKeys()
ClearEvalSumKeys()
ClearEvalAutomorphismKeys()
ReleaseAllContexts()

Note that this will invalidate all currently existing contexts, even those which are still in use. Thus you should only call these functions once you are done with a given FHE setup and want to start a new one. For more details, please refer to the documentation for ClearEvalMultKeys, ClearEvalSumKeys, ClearEvalAutomorphismKeys, and ReleaseAllContexts.

Therefore, for a full cleanup of all OpenFHE-occupied memory, first ensure that all variables holding references to OpenFHE objects are out of scope and then execute

ClearEvalMultKeys()
ClearEvalSumKeys()
ClearEvalAutomorphismKeys()
ReleaseAllContexts()
GC.gc()

By running these commands at appropriate points in your code, you can prevent excessive memory usage and ensure efficient memory management when using OpenFHE.jl.

By default, OpenFHE.jl uses the OpenFHE-julia library provided by the openfhe_julia_jll.jl package, which is automatically obtained when installing OpenFHE.jl. Someimtes, however, it might be beneficial to instead use a system-provided OpenFHE-julia library, e.g., for development or performance purposes. You can change the default by providing a different library with the OpenFHE.set_library! function, i.e., by running

julia> using OpenFHE

julia> OpenFHE.set_library!("/abs/path/to/library.so")
[ Info: Please restart Julia and reload OpenFHE.jl for the library changes to take effect

This will create a LocalPreferences.toml file in your current project directory with the libopenfhe_julia preference set accordingly. As advised, you need to restart Julia for the change to take effect. By calling set_library!() without an argument, you revert to using JLL-provided library again.

In case the custom library has been deleted, loading OpenFHE.jl will fail. In that case, either remove the LocalPreferences.toml file or manually reset the preferences by executing

julia> using UUIDs, Preferences

julia> delete_preferences!(UUID("77ce9b8e-ecf5-45d1-bd8a-d31f384f2f95"), # UUID of OpenFHE.jl
                           "libopenfhe_julia"; force = true)

OpenFHE.jl using CxxWrap.jl to wrap the C++ library OpenFHE for use in Julia. In general, we try to stick as close to the original library's names and conentions as possible. Since some concepts of C++ do not directly translate to Julia, however, some differences are unavoidable. The most notable one is likely that Julia does not know the concept of class member functions. CxxWrap.jl (and OpenFHE.jl) translates this to Julia functions that expect the object as its first argument. Thus, a C++ member function call

my_object.member_function(arg1, arg2);

will look like

member_function(my_object, arg1, arg2)

in Julia.

To simplify switching back and forth between OpenFHE.jl and the C++ library OpenFHE, OpenFHE.jl tries to use the same type and function names as OpenFHE. Since PascalCase is used for types and functions in OpenFHE, the same style is used in OpenFHE.jl, even though this is contrary to typical Julia best practices (where PascalCase is only used for types and snake_case is used for functions).

Furthermore, all OpenFHE types are wrapped by corresponding CxxWrap.jl types, which can sometimes be very verbose. To reduce clutter in the Julia REPL, OpenFHE.jl thus often uses a simpler canonical output when printing an object. For example, the output of GenCryptoContext(parameters) is an object of type CxxWrap.StdLib.SharedPtrAllocated{CryptoContextImpl{DCRTPoly}}, but when showing the object we just print SharedPtr{CryptoContext{DCRTPoly}}(). To find out the actual underlying type, use typeof.

If you use OpenFHE.jl in your own research, please cite this repository as follows:

@misc{schlottkelakemper2024openfhejulia,
  title={{O}pen{FHE}.jl: {F}ully homomorphic encryption in {J}ulia using {O}pen{FHE}},
  author={Schlottke-Lakemper, Michael},
  year={2024},
  howpublished={\url{https://github.com/hpsc-lab/OpenFHE.jl}},
  doi={10.5281/zenodo.10460452}
}

OpenFHE.jl was initiated by Michael Schlottke-Lakemper (University of Augsburg, Germany), who is also its principal maintainer.

Further contributions to OpenFHE.jl have been made by the following people:

• Arseniy Kholod (RWTH Aachen University, Germany)

OpenFHE.jl is available under the MIT license (see LICENSE.md). OpenFHE itself is available under the BSD 2-Clause license.

Contributions by the community are very welcome! A good start would be to compare the examples folder in OpenFHE.jl (link) and in OpenFHE (link) and to port a missing example file to OpenFHE.jl. In case some OpenFHE functionality is not yet exposed by OpenFHE-julia, it would have to be added there first.