Public key authenticated encryption in Rust

This is an example implementation of public key authenticated encryption (PKAE) in Rust using only the high performance Ring cryptography library.

PKAE enables a person or service X to send confidential data to another person or service Y such that only Y can read the data. Y can also verify that the data originated from X and not an impostor.

Motivation

Both the libsodium and openssl libraries can perform PKAE using specific primitives, however these are easy to misuse and call a lot of potentially unsafe C code. No such similar examples to perform PKAE exist for ring. Also, the Rust interfaces to libsodium and openssl require the full libraries which substantially increase code size. Finally, many Rust crates already depend on ring directly or transitively, including rustls and by extension actix-net, actix-web, tokio-rustls, h2, and reqwest. Writing PKAE functionality using ring avoids having to bring in a separate dependency.

Documentation

The implementation is short and each function is documented, so the best documentation is the code itself. A browsable rustdoc version can also be created using cargo rustdoc -- --document-private-items.

Building and running the code

Type cargo run. If the code encrypts and decrypts the message successfully, it should print Ok.