ring for Rust: A Complete Guide with Examples

What It Is and Why You Need It

ring is a cryptographic library for the Rust language, providing secure, audited, and high-performance implementations of core cryptographic primitives. It is based on the BoringSSL codebase (a fork of OpenSSL by Google) and is designed with a focus on security, ease of use, and minimizing the attack surface. Unlike more general libraries such as openssl or rust-crypto, ring intentionally limits the set of supported algorithms, excluding outdated or insecure ones (e.g., DES, RC4, MD5), which reduces the risk of accidentally using weak cryptography.

Why do you need ring? If you are developing a Rust application that requires hashing (SHA-256, SHA-512), symmetric encryption (AES-GCM, ChaCha20-Poly1305), asymmetric encryption and signatures (RSA, ECDSA, Ed25519), random number generation, or key agreement (X25519, ECDH), ring is the optimal choice. It is actively used in projects such as rustls (a TLS implementation in Rust), reqwest (an HTTP client), and webpki (certificate validation). The library has no external dependencies (except libc on Linux/macOS) and compiles with Cargo, making it ideal for embedded systems and cross-compilation.

Key advantages of ring: security (continuous auditing, no insecure algorithms), performance (uses optimized assembly routines from BoringSSL), and API simplicity (minimal number of types and functions, clear documentation). ring does not provide high-level abstractions such as certificate or protocol handling — separate crates exist for those purposes. Instead, it provides building blocks that can be safely combined.

Installation

To add ring to your Rust project, run the following command in the project's root directory:

cargo add ring

Or manually add it to your Cargo.toml file:

[dependencies]\nring = "0.17"

At the time of writing, the current version is 0.17.x. Make sure you have Rust installed (rustc 1.70+). ring requires a C compiler (gcc, clang, or msvc) to build the native BoringSSL components. On Windows, you may need to install Build Tools for Visual Studio.

Quick Start — Minimal Working Example

Create a new project and replace the contents of src/main.rs with the following code, which computes the SHA-256 hash of a string:

use ring::digest::{Context, SHA256};\nuse ring::rand::SystemRandom;\n\nfn main() {\n    // SHA-256 hashing\n    let mut context = Context::new(&SHA256);\n    context.update("Hello, ring!".as_bytes());\n    let digest = context.finish();\n    println!("SHA-256: {:?}", digest);\n\n    // Generating random bytes\n    let rng = SystemRandom::new();\n    let mut random_bytes = [0u8; 32];\n    ring::rand::fill(&rng, &mut random_bytes).unwrap();\n    println!("Random bytes: {:02x?}", random_bytes);\n}

Run the program with the command cargo run. You will see the SHA-256 hash and 32 random bytes in hexadecimal format.

Core Methods/Functions

1. ring::digest::digest

Signature: pub fn digest(algorithm: &'static Algorithm, data: &[u8]) -> Digest

Description: Computes the hash of the data using the specified algorithm (SHA256, SHA384, SHA512, SHA1). This is a one-shot function for simple cases.

use ring::digest::{digest, SHA256};\n\nlet data =