Building cryptographic libraries requires precision and security. Rust provides tools that help create robust systems. I’ve found these eight techniques essential for developing high-assurance cryptography in Rust.

Constant-time operations prevent timing attacks. When comparing sensitive data like authentication tags, every operation must take fixed time. This code snippet shows how:

fn constant_time_compare(a: &[u8], b: &[u8]) -> bool {
    if a.len() != b.len() {
        return false;
    }
    let mut diff = 0u8;
    for (x, y) in a.iter().zip(b) {
        diff |= x ^ y;
    }
    diff == 0
}

Secure memory handling ensures sensitive data doesn’t linger. I always implement custom Drop traits for keys:

struct PrivateKey([u8; 32]);

impl Drop for PrivateKey {
    fn drop(&mut self) {
        for byte in &mut self.0 {
            *byte = 0;
        }
    }
}

fn generate_key() -> PrivateKey {
    let mut key = [0u8; 32];
    getrandom::getrandom(&mut key).unwrap();
    PrivateKey(key)
}

Side-channel resistant arithmetic avoids data-dependent branches. Cryptographic operations shouldn’t leak information through execution time. This conditional swap works without branching:

fn conditional_swap(a: &mut u32, b: &mut u32, swap: bool) {
    let mask = -(swap as i32) as u32;
    let diff = *a ^ *b;
    *a ^= mask & diff;
    *b ^= mask & diff;
}

Fuzzing-resistant parsing handles untrusted input safely. I structure validation to avoid secret-dependent control flow:

fn decode_point(input: &[u8]) -> Option<[u8; 32]> {
    if input.len() != 32 { 
        return None;
    }
    let mut buffer = [0u8; 32];
    buffer.copy_from_slice(input);
    Point::validate(&buffer)
}

Hardware acceleration boosts performance securely. Rust’s intrinsics access CPU features directly. This AES implementation uses x86 instructions:

#[target_feature(enable = "aes")]
unsafe fn aes_encrypt(block: &mut [u8; 16], key: &AesKey) {
    use std::arch::x86_64::*;
    let mut state = _mm_loadu_si128(block.as_ptr() as *const _);
    for round_key in &key.round_keys {
        state = _mm_aesenc_si128(state, _mm_loadu_si128(round_key.as_ptr() as *const _));
    }
    _mm_storeu_si128(block.as_mut_ptr() as *mut _, state);
}

Formal verification hooks enable mathematical assurance. I integrate property tests directly into development:

#[quickcheck]
fn test_key_agreement(secret1: [u8; 32], secret2: [u8; 32]) -> bool {
    let pubkey1 = generate_public_key(&secret1);
    let shared1 = derive_shared_secret(&secret1, &pubkey1);
    let shared2 = derive_shared_secret(&secret2, &pubkey1);
    shared1 != shared2
}

Compile-time algorithm selection maintains flexibility. Feature flags let users choose implementations:

#[cfg(feature = "sha2")]
type HashAlg = sha2::Sha256;

#[cfg(feature = "blake2")]
type HashAlg = blake2::Blake2b;

fn compute_digest(data: &[u8]) -> [u8; 32] {
    let mut hasher = HashAlg::new();
    hasher.update(data);
    hasher.finalize().into()
}

Memory protection locks sensitive regions. System calls prevent swapping or debugging access:

fn lock_pages(addr: *mut u8, len: usize) {
    unsafe {
        libc::mlock(addr as *const libc::c_void, len);
    }
}

struct SecureBuffer {
    ptr: *mut u8,
    size: usize,
}

impl SecureBuffer {
    fn new(size: usize) -> Self {
        let buffer = unsafe {
            libc::mmap(
                std::ptr::null_mut(),
                size,
                libc::PROT_READ | libc::PROT_WRITE,
                libc::MAP_PRIVATE | libc::MAP_ANONYMOUS,
                -1,
                0,
            ) as *mut u8
        };
        Self { ptr: buffer, size }
    }

    fn lock(&self) {
        lock_pages(self.ptr, self.size);
    }
}

These approaches combine Rust’s safety features with cryptographic best practices. The type system prevents many common errors, while zero-cost abstractions maintain performance. I’ve seen these techniques prevent entire classes of vulnerabilities in production systems. Cryptographic security demands multiple layers of protection—Rust provides the tools to implement them effectively.