rns-crypto 0.2.2

#![cfg_attr(not(feature = "std"), no_std)]
extern crate alloc;

pub mod aes128;
pub mod aes256;
#[cfg(target_arch = "x86_64")]
mod aes256_ni;
pub mod ed25519;
pub mod hkdf;
pub mod hmac;
pub mod identity;
pub mod pkcs7;
pub mod ratchet;
pub mod sha256;
#[cfg(target_arch = "x86_64")]
mod sha256_x2;
pub mod sha512;
pub mod stamp_value;
pub mod token;
pub mod x25519;

/// Trait for random number generation.
/// Callers provide an implementation; in `std` builds this wraps OS randomness.
pub trait Rng {
    fn fill_bytes(&mut self, dest: &mut [u8]);
}

/// Deterministic RNG for testing.
pub struct FixedRng {
    bytes: alloc::vec::Vec<u8>,
    pos: usize,
}

impl FixedRng {
    pub fn new(bytes: &[u8]) -> Self {
        Self {
            bytes: bytes.to_vec(),
            pos: 0,
        }
    }
}

impl Rng for FixedRng {
    fn fill_bytes(&mut self, dest: &mut [u8]) {
        for b in dest.iter_mut() {
            *b = self.bytes[self.pos % self.bytes.len()];
            self.pos += 1;
        }
    }
}

/// OS-backed RNG: the kernel's generator through getrandom(3) on Linux
/// (served without a system call where the C library and kernel support it),
/// `/dev/urandom` elsewhere, the hardware RNG on ESP-IDF.
#[cfg(feature = "std")]
pub struct OsRng;

#[cfg(feature = "std")]
impl Rng for OsRng {
    fn fill_bytes(&mut self, dest: &mut [u8]) {
        // ESP-IDF: use hardware RNG via esp_fill_random
        #[cfg(target_os = "espidf")]
        {
            unsafe {
                esp_idf_sys::esp_fill_random(
                    dest.as_mut_ptr() as *mut core::ffi::c_void,
                    dest.len(),
                );
            }
        }
        #[cfg(target_os = "linux")]
        {
            let mut rest = dest;
            while !rest.is_empty() {
                // SAFETY: `rest` is valid for writes of `rest.len()` bytes.
                let n = unsafe { libc::getrandom(rest.as_mut_ptr().cast(), rest.len(), 0) };
                if n < 0 {
                    let error = std::io::Error::last_os_error();
                    if error.kind() == std::io::ErrorKind::Interrupted {
                        continue;
                    }
                    panic!("getrandom failed: {error}");
                }
                rest = &mut rest[n as usize..];
            }
        }
        #[cfg(not(any(target_os = "espidf", target_os = "linux")))]
        {
            use std::io::Read;
            // Opened once: opening it for every draw cost an open and a close
            // per token IV and random hash. Reads through `&File` need no lock.
            static URANDOM: std::sync::OnceLock<std::fs::File> = std::sync::OnceLock::new();
            let mut f = URANDOM.get_or_init(|| {
                std::fs::File::open("/dev/urandom").expect("Failed to open /dev/urandom")
            });
            f.read_exact(dest)
                .expect("Failed to read from /dev/urandom");
        }
    }
}

#[cfg(all(test, feature = "std", not(target_os = "espidf")))]
mod tests {
    use super::{OsRng, Rng};

    #[test]
    fn os_rng_fills_large_and_empty_buffers() {
        let mut empty = [0u8; 0];
        OsRng.fill_bytes(&mut empty);
        let mut large = std::vec![0u8; 1 << 20];
        OsRng.fill_bytes(&mut large);
        // Every 64 KiB window holds random bytes, so no part was skipped.
        assert!(large
            .chunks(1 << 16)
            .all(|chunk| chunk.iter().any(|&b| b != 0)));
    }

    #[test]
    fn os_rng_fills_buffers_from_concurrent_threads() {
        let draws: std::vec::Vec<[u8; 32]> = (0..8)
            .map(|_| {
                std::thread::spawn(|| {
                    let mut out = [0u8; 32];
                    OsRng.fill_bytes(&mut out);
                    out
                })
            })
            .collect::<std::vec::Vec<_>>()
            .into_iter()
            .map(|thread| thread.join().unwrap())
            .collect();
        for (i, a) in draws.iter().enumerate() {
            assert_ne!(a, &[0u8; 32]);
            for b in &draws[i + 1..] {
                assert_ne!(a, b);
            }
        }
    }
}

/// Set up aws-lc once, before its first use: its CPU feature detection.
#[cfg(all(
    any(feature = "x25519-aws-lc", feature = "ed25519-aws-lc"),
    any(target_arch = "x86_64", target_arch = "aarch64")
))]
pub(crate) fn aws_lc_init() {
    static INIT: std::sync::Once = std::sync::Once::new();
    // SAFETY: takes no arguments; sets up aws-lc's CPU feature detection.
    INIT.call_once(|| unsafe { aws_lc_sys::CRYPTO_library_init() });
}