Limitations

OpenFHE

See the Security Notes for Homomorphic Encryption in OpenFHE’s documentation.

Rust wrapper

At the moment, only a certain set of OpenFHE functionality has been implemented.

We use the CXX crate for our Rust binding to reduce the amount of abstraction levels. OpenFHE types are represented as opaque types on the Rust side using cxx::UniquePtr from the CXX crate. Instead of the usual std::vec, we use cxx::CxxVector for primitive types, and also cxx::CxxVector<ComplexPair> for representing std::vector<std::complex<double>> type.

The main difference lies in the current cxx::CxxVector supported functional, limited compared to std::vector, e.g. you need to init cxx::CxxVector element by element. Since cxx currently does not support cxx::CxxVector of opaque types, we are using a separate type for each vector of opaque type. Since CXX currently does not support alternatives for std::unordered_map and std::map, we are using separate types for them. The implementations of these types are very simple because we are planning to switch CXX variants further. But before switching these types can be extended to support basic functional of std::vector, std::map and std::unordered_map if required.

Since Rust does not support default parameters and function overloading, default parameters are mentioned in comments after the corresponding parameter name, and overloaded functions are represented by slightly different names. Calling member functions of instances, generated by GenNull… functions results in undefined behavior.

Since CXX crate has limited support for function pointers (only functions without a return type are supported), EvalChebychevFunction expects fn(f64, ret: &mut f64) as the callable object.