Crate he_ring

Expand description

§he-ring, a toolkit library to build Homomorphic Encryption

Building on feanor-math, this library provides efficient implementations of various building blocks for Homomorphic Encryption (HE). The focus is on implementations of the ring R_q = Z[X]/(Phi_n(X), q) as required for second-generation HE schemes (like BGV, BFV), but also contains many other components and schemes.

The goal of this library is not to provide an easy-to-use implementation of homomorphic encryptions for use in applications - there are many good libraries for that already. Instead, the goal is to provide a toolkit for researchers that simplifies implementing variants of existing HE schemes, as well as new HE schemes.

§Features

In short, he-ring contains the following:

multiple efficient implementations of arithmetic in the ring R_q, which provide different performance characteristics (supporting arbitrary n)
an implementation of the isomorphism R/(p^e) = GR(p, e, d) x ... x GR(p, e, d) via “hypercube structures” (compare “Bootstrapping for HElib” by Halevi and Shoup, https://ia.cr/2014/873)
an implementation of “gadget products”, i.e. the certain kind of inner product that is used in HE schemes to multiply ciphertexts with lower noise growth
implementations of the BFV and BGV encryption schemes
bootstrapping for BFV and BGV
tools for arithmetization, including modelling of arithmetic circuits, polynomial-to-circuit conversion via Paterson-Stockmeyer and HElib-style linear transforms

The following features are available partially, and/or WIP:

Noise estimation and optional automated modulus-switching for BGV

§Examples

In addition to the API documentation, detailed guides and examples to some parts of HE-Ring can be found in crate::examples.

§Notation (comparison with HElib)

We sometimes use notation differently from the way it is used in HElib, and follow instead most modern HE literature. In particular, we use the following letters:

HE-Ring	HElib	Meaning
`n`	`m`	Index (sometimes conductor) of the cyclotomic number ring
`digits`	`c`	Number of parts to decompose into during gadget products
`log2(q)`	`bits`	Size of the ciphertext modulus
`p`	`p`	Prime factor of the plaintext modulus
`r`	`r`	Exponent of the plaintext modulus
`t`	none	Plaintext modulus `p^r`
`m[i]`	`ords[i]`	Length of the `i`-th hypercube dimension

§Performance

When optimizing for performance, please use the Intel HEXL library (by enabling the feature use_hexl and providing a build of HEXL, as described in more detail in the documentation of feanor-math-hexl), since the default NTT does not provide SOTA performance. Also note that he-ring is currently single-threaded.

Note that while this library is already quite optimized, it may not be fully competitive with other HE libraries that have existed for longer and thus received more optimization effort. Also, our goal of providing a modular toolkit of building blocks makes some kinds of optimizations more difficult, since components cannot always make as many assumptions on the input as they could if they only support a single HE scheme.

§Profiling

he-ring is instrumented using the framework defined by the Rust library tracing. Hence, running any he-ring functions with an active tracing subscriber will generate corresponding tracing events that the subscriber can use for profiling purposes. There are various crates that implement tracing subscribers with profiling functionality.

For tests within this crate, we use tracing-chrome which generates Perfetto json trace files (can be displayed by Google Chrome without requiring plugins). In particular, if you enable ignored tests and run one of the measure_time_-prefixed test in this crate, this will generate a trace file. Of course, this is only included on test builds, in library builds, the parent application is free to configure tracing as desired.

§Disclaimer

This library has been designed for research on homomorphic encryption. I did not have practical considerations (like side-channel resistance) in mind, and advise against using using it in production.

§How to cite HE-Ring

Please use the following bibtex entry to cite HE-Ring:

@misc{hering,
    title = {{HE-Ring}: A homomorphic encryption library},
    url = {https://github.com/FeanorTheElf/he-ring},
    author = {Hiroki Okada and Rachel Player and Simon Pohmann},
    year = {2025}
}

§License

he-ring is licensed under the MIT license.

Modules§

bfv: Contains an implementation of the BFV scheme.
bgv: Contains an implementation of the BGV scheme.
ciphertext_ring: Implementation of rings using double-RNS representation.
circuit: The implementation of arithmetic-galois circuits (i.e. circuits built from linear combination, multiplication and galois gates).
cyclotomic: Defines the trait cyclotomic::CyclotomicRing for rings of the form R[X]/(Phi_n), where R is any base ring.
digitextract: Contains algorithms to build arithmetic circuits, with a focus on digit extraction polynomials.
examples: This is a workaround for displaying examples on docs.rs.
gadget_product: Contains an implementation of “gadget products”, which are a form of inner products that are commonly used in HE to compute multiplications of noisy values in a way that reduces the increase in noise.
lintransform: Contains algorithms to compute linear transformations and represent them as linear combination of Galois automorphisms, as required for (second-generation) HE schemes.
ntt: Contains an abstraction for NTTs and convolutions, which can then be used to configure the ring implementations in this crate.
number_ring: Contains an HE-specific abstraction for number rings.
rnsconv: Implementation of fast RNS conversion algorithms.

Macros§

impl_deserialize_seed_for_dependent_enum: Same as impl_deserialize_seed_for_dependent_struct! but for enums.
impl_deserialize_seed_for_dependent_struct: Macro to implement serde::de::DeserializeSeed for a custom type.

Functions§

log_time: Runs the given function. If LOG is true, its running time is printed to stdout.

Type Aliases§

DefaultCiphertextAllocator: The default allocator for ciphertext ring elements, which will be used by all tests and benchmarks. It is also a good choice when instantiating homomorphic encryption as a user.
DefaultConvolution: The default convolution algorithm that will be used by all tests and benchmarks. It is also a good choice when instantiating homomorphic encryption as a user.
DefaultNegacyclicNTT: The default algorithm for computing negacyclic NTTs that will be used by all tests and benchmarks. It is also a good choice when instantiating homomorphic encryption as a user.

Crate he_ringCopy item path