Building Secure Rust Applications with Ring: Memory-Safe Cryptography for Modern Developers

Source: Dev.to

Introduction

When you write code that handles secrets—passwords, financial data, private messages—you can’t afford mistakes. A tiny slip, such as a misplaced byte or a timing difference, can break everything. Historically, cryptography has been a daunting task because many libraries are written in C, which trusts the programmer completely. Buffer overflows, memory leaks, and side‑channel attacks are common pitfalls.

Why Rust and Ring?

Rust stops entire categories of errors before your code even runs. The Ring crate builds on Rust’s safety guarantees, offering cryptographic primitives with a safety‑first mindset. Its core is written in safe Rust, and the small C components that remain are heavily reviewed and constant‑time, eliminating many classes of vulnerabilities by design.

Core Features

• Hash functions: SHA‑256, SHA‑512, etc.
• Secure random number generation.
• Digital signatures: Ed25519 and others.
• Key agreement: Diffie‑Hellman, X2550.
• Password hashing: PBKDF2.

Generating Secure Random Numbers

In cryptography you need unpredictable randomness. Ring provides a straightforward API that uses the operating system’s secure source.

use ring::rand;

fn get_secure_random() -> Result {
    let rng = rand::SystemRandom::new();
    let mut random_bytes = [0u8; 32]; // 32 random bytes
    rng.fill(&mut random_bytes)?;
    Ok(random_bytes)
}

SystemRandom reads from /dev/urandom on Linux (or the platform‑specific source) and guarantees that either the operation succeeds or returns an error—no hidden failure modes.

Password Hashing with PBKDF2

Never store passwords directly. Store a salted, deliberately slow hash to defend against rainbow‑table attacks. Ring provides the PBKDF2 primitive.

use ring::{digest, pbkdf2};
use std::num::NonZeroU32;

fn hash_password(password: &str, salt: &[u8]) -> Vec {
    let iterations = NonZeroU32::new(100_000).expect("Non-zero iteration count");
    let mut derived_key = vec![0u8; digest::SHA256.output_len]; // 32‑byte output

    pbkdf2::derive(
        pbkdf2::PBKDF2_HMAC_SHA256,
        iterations,
        salt,
        password.as_bytes(),
        &mut derived_key,
    );

    derived_key
}

fn verify_password(password: &str, salt: &[u8], stored_hash: &[u8]) -> bool {
    let iterations = NonZeroU32::new(100_000).unwrap();
    pbkdf2::verify(
        pbkdf2::PBKDF2_HMAC_SHA256,
        iterations,
        salt,
        password.as_bytes(),
        stored_hash,
    )
    .is_ok()
}

NonZeroU32 ensures the iteration count can never be zero, preventing a critical security mistake at compile time. Each password should have a unique, random salt stored alongside the derived hash.

Digital Signatures

Signatures verify authenticity and integrity. Ring supports modern algorithms like Ed25519.

use ring::{rand, signature};
use ring::signature::KeyPair;

fn sign_a_message() -> Result> {
    // 1. Secure RNG
    let rng = rand::SystemRandom::new();

    // 2. Generate a private/public key pair (PKCS#8)
    let pkcs8_bytes = signature::Ed25519KeyPair::generate_pkcs8(&rng)?;

    // 3. Create a key pair object
    let key_pair = signature::Ed25519KeyPair::from_pkcs8(pkcs8_bytes.as_ref())?;

    // Public key (shareable)
    let public_key_bytes = key_pair.public_key().as_ref();

    // 4. Sign a message
    let message = b"Critical system update v2.1";
    let signature = key_pair.sign(message);

    // 5. Verification (performed by the receiver)
    let peer_public_key = signature::UnparsedPublicKey::new(&signature::ED25519, public_key_bytes);
    match peer_public_key.verify(message, signature.as_ref()) {
        Ok(()) => println!("Signature is valid. Update is authentic."),
        Err(_) => println!("DANGER: Signature verification failed!"),
    }

    Ok(())
}

The private key (pkcs8_bytes) must remain secret, while the public key can be distributed freely. The API enforces this separation clearly.

Comparison with OpenSSL

OpenSSL is a massive library written in C. Its breadth brings complexity and a history of severe bugs (e.g., Heartbleed). Ring takes a different approach:

• Smaller, curated API: Only modern, vetted algorithms.
• Memory safety: Rust code eliminates many classes of bugs.
• Constant‑time implementations: Reduces side‑channel risks.

This focused design guides developers toward correct, secure usage without the overhead of legacy options.

Key Agreement (Diffie‑Hellman)

Ring also provides safe key‑exchange primitives (e.g., X25519). While a full example is beyond this excerpt, the typical workflow involves:

1. Generating an ephemeral key pair.
2. Exchanging the public keys.
3. Deriving a shared secret with agreement::agree_ephemeral.

All operations are constant‑time and use safe Rust abstractions.