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//! AES-CMAC algorithms backed by wolfCrypt's CMAC_CTX API.
//!
//! Each type implements the RustCrypto [`digest`](digest_trait) 0.10 MAC traits
//! (`OutputSizeUser`, `KeySizeUser`, `KeyInit`, `Update`, `FixedOutput`,
//! `MacMarker`) so they satisfy the blanket `Mac` impl automatically.
//!
//! Callers should `use digest_trait::Mac` for the full API:
//! `new_from_slice()`, `update()`, `finalize()`, `verify_slice()`.
use core::ffi::c_void;
use digest_trait::{FixedOutput, KeyInit, OutputSizeUser, Update};
use generic_array::GenericArray;
use typenum::*;
/// Internal macro that stamps out a complete AES-CMAC wrapper for one key size.
///
/// The generated struct holds a heap-allocated `CMAC_CTX` and delegates
/// all operations to wolfCrypt through the OpenSSL-compat CMAC layer.
macro_rules! impl_cmac {
(
$name:ident,
$cipher_fn:path,
$key_size:ty,
$cfg_gate:meta
) => {
#[$cfg_gate]
pub struct $name {
ctx: *mut wolfcrypt_rs::CMAC_CTX,
}
// SAFETY: CMAC_CTX is heap-allocated and only accessed through
// &self / &mut self. wolfCrypt's CMAC layer is thread-safe when a
// context is used from a single thread, which Rust's ownership
// rules enforce.
#[$cfg_gate]
unsafe impl Send for $name {}
#[$cfg_gate]
impl $name {
/// Return the cipher descriptor pointer for this CMAC's AES variant.
#[inline]
fn evp_cipher() -> *const wolfcrypt_rs::EVP_CIPHER {
// SAFETY: EVP_aes_*_cbc functions return a static const pointer.
unsafe { $cipher_fn() }
}
}
// ------------------------------------------------------------------
// core / RustCrypto trait impls
// ------------------------------------------------------------------
#[$cfg_gate]
impl Drop for $name {
fn drop(&mut self) {
// SAFETY: self.ctx was allocated via CMAC_CTX_new and
// is only freed once here.
unsafe {
wolfcrypt_rs::CMAC_CTX_free(self.ctx);
}
}
}
#[$cfg_gate]
impl OutputSizeUser for $name {
// CMAC output is always one AES block = 16 bytes.
type OutputSize = U16;
}
#[$cfg_gate]
impl crypto_common::KeySizeUser for $name {
type KeySize = $key_size;
}
#[$cfg_gate]
impl KeyInit for $name {
/// Create from a fixed-size key (KeySize bytes).
fn new(key: &GenericArray<u8, <Self as crypto_common::KeySizeUser>::KeySize>) -> Self {
Self::init_with_key(key.as_slice())
.expect("CMAC_Init failed with correct key size")
}
/// Create from a variable-length key.
/// Returns `InvalidLength` if `key.len()` does not match the
/// expected AES key size.
fn new_from_slice(key: &[u8]) -> Result<Self, crypto_common::InvalidLength> {
Self::init_with_key(key).ok_or(crypto_common::InvalidLength)
}
}
#[$cfg_gate]
impl $name {
/// Shared initialisation: allocate a CMAC_CTX and key it.
/// Returns `None` if the key length is wrong or allocation fails.
fn init_with_key(key: &[u8]) -> Option<Self> {
use typenum::Unsigned;
let expected_len = <$key_size as Unsigned>::USIZE;
if key.len() != expected_len {
return None;
}
// SAFETY: CMAC_CTX_new returns a heap-allocated context
// or NULL on OOM.
let ctx = unsafe { wolfcrypt_rs::CMAC_CTX_new() };
if ctx.is_null() {
return None;
}
// SAFETY: ctx is non-null and freshly allocated. key pointer
// and length are guaranteed correct by the slice reference.
// CMAC_Init with a non-null key sets the key and cipher.
let rc = unsafe {
wolfcrypt_rs::CMAC_Init(
ctx,
key.as_ptr() as *const c_void,
key.len(),
Self::evp_cipher(),
core::ptr::null_mut(),
)
};
if rc != 1 {
unsafe { wolfcrypt_rs::CMAC_CTX_free(ctx) };
return None;
}
Some(Self { ctx })
}
}
#[$cfg_gate]
impl Update for $name {
fn update(&mut self, data: &[u8]) {
// SAFETY: self.ctx is valid. data pointer and length are
// guaranteed correct by the slice reference.
unsafe {
let rc = wolfcrypt_rs::CMAC_Update(
self.ctx,
data.as_ptr(),
data.len(),
);
assert_eq!(rc, 1, "CMAC_Update failed (context not initialized)");
}
}
}
#[$cfg_gate]
impl FixedOutput for $name {
fn finalize_into(self, out: &mut GenericArray<u8, Self::OutputSize>) {
let mut len: usize = 0;
// SAFETY: out is exactly OutputSize (16) bytes. self.ctx is
// valid. After this call, Drop will free the context.
unsafe {
let rc = wolfcrypt_rs::CMAC_Final(
self.ctx,
out.as_mut_ptr(),
&mut len,
);
assert_eq!(rc, 1, "CMAC_Final failed (context not initialized)");
}
debug_assert_eq!(len, 16);
// Drop runs after this and frees self.ctx.
}
}
#[$cfg_gate]
impl digest_trait::MacMarker for $name {}
};
}
// ======================================================================
// Stamp out both AES-CMAC types
// ======================================================================
impl_cmac!(
WolfCmacAes128,
wolfcrypt_rs::EVP_aes_128_cbc,
U16,
cfg(all(wolfssl_openssl_extra, wolfssl_cmac))
);
impl_cmac!(
WolfCmacAes256,
wolfcrypt_rs::EVP_aes_256_cbc,
U32,
cfg(all(wolfssl_openssl_extra, wolfssl_cmac))
);