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Assert that MLKEM APIs generate real keys #470

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3b77f5d
Add missing error handling in ML-KEM generate
kornelski Feb 10, 2026
7a093bc
Avoid large-ish stack copies in encapsulate()
kornelski Feb 10, 2026
60c5ea6
Ensure we don't leave unit memory if generate_key fails
kornelski Feb 10, 2026
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124 changes: 48 additions & 76 deletions boring/src/mlkem.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -91,14 +91,14 @@ impl MlKemPrivateKey {
pub fn generate(algorithm: Algorithm) -> Result<(MlKemPublicKey, MlKemPrivateKey), ErrorStack> {
match algorithm {
Algorithm::MlKem768 => {
let (pk, sk) = MlKem768PrivateKey::generate();
let (pk, sk) = MlKem768PrivateKey::generate()?;
Ok((
MlKemPublicKey(Either::MlKem768(pk)),
MlKemPrivateKey(Either::MlKem768(sk)),
))
}
Algorithm::MlKem1024 => {
let (pk, sk) = MlKem1024PrivateKey::generate();
let (pk, sk) = MlKem1024PrivateKey::generate()?;
Ok((
MlKemPublicKey(Either::MlKem1024(pk)),
MlKemPrivateKey(Either::MlKem1024(sk)),
Expand Down Expand Up @@ -131,16 +131,20 @@ impl MlKemPublicKey {
/// Encapsulates a shared secret to the given public key, returning
/// `(ciphertext, shared_secret)`.
pub fn encapsulate(&self) -> Result<(Vec<u8>, MlKemSharedSecret), ErrorStack> {
match &self.0 {
let mut ss = [0; SHARED_SECRET_BYTES];
let ct = match &self.0 {
Either::MlKem768(pk) => {
let (ct, ss) = pk.encapsulate();
Ok((ct.to_vec(), ss))
let mut ct = vec![0; MlKem768PrivateKey::CIPHERTEXT_BYTES];
pk.encapsulate_into(ct.as_mut_slice().try_into().unwrap(), &mut ss);
ct
}
Either::MlKem1024(pk) => {
let (ct, ss) = pk.encapsulate();
Ok((ct.to_vec(), ss))
let mut ct = vec![0; MlKem1024PrivateKey::CIPHERTEXT_BYTES];
pk.encapsulate_into(ct.as_mut_slice().try_into().unwrap(), &mut ss);
ct
}
}
};
Ok((ct, ss))
}

/// Query public key and ciphertext length
Expand Down Expand Up @@ -222,39 +226,27 @@ impl MlKem768PrivateKey {
pub const CIPHERTEXT_BYTES: usize = ffi::MLKEM768_CIPHERTEXT_BYTES as usize;

/// Generate a new key pair.
#[must_use]
fn generate() -> (Box<MlKem768PublicKey>, Box<MlKem768PrivateKey>) {
fn generate() -> Result<(Box<MlKem768PublicKey>, Box<MlKem768PrivateKey>), ErrorStack> {
// SAFETY: all buffers are out parameters, correctly sized
unsafe {
ffi::init();
let mut public_key_bytes: MaybeUninit<[u8; MlKem768PublicKey::PUBLIC_KEY_BYTES]> =
MaybeUninit::uninit();
let mut seed: MaybeUninit<MlKemPrivateKeySeed> = MaybeUninit::uninit();
let mut bytes = [0; MlKem768PublicKey::PUBLIC_KEY_BYTES];
let mut seed = [0; PRIVATE_KEY_SEED_BYTES];
let mut expanded: MaybeUninit<ffi::MLKEM768_private_key> = MaybeUninit::uninit();

ffi::MLKEM768_generate_key(
public_key_bytes.as_mut_ptr().cast(),
seed.as_mut_ptr().cast(),
bytes.as_mut_ptr().cast(),
seed.as_mut_ptr(),
expanded.as_mut_ptr(),
);

let bytes = public_key_bytes.assume_init();

// Parse the public key bytes to get the parsed struct
let mut cbs = cbs_init(&bytes);
let mut parsed: MaybeUninit<ffi::MLKEM768_public_key> = MaybeUninit::uninit();
ffi::MLKEM768_parse_public_key(parsed.as_mut_ptr(), &mut cbs);

(
Box::new(MlKem768PublicKey {
bytes,
parsed: parsed.assume_init(),
}),
Ok((
Box::new(MlKem768PublicKey::from_slice(&bytes)?),
Box::new(MlKem768PrivateKey {
seed: seed.assume_init(),
seed,
expanded: expanded.assume_init(),
}),
)
))
}
}

Expand Down Expand Up @@ -388,25 +380,19 @@ impl MlKem768PublicKey {
}

/// Encapsulate: returns (ciphertext, shared_secret).
fn encapsulate(
fn encapsulate_into(
&self,
) -> (
[u8; MlKem768PrivateKey::CIPHERTEXT_BYTES],
MlKemSharedSecret,
ciphertext: &mut [u8; MlKem768PrivateKey::CIPHERTEXT_BYTES],
shared_secret: &mut MlKemSharedSecret,
) {
// SAFETY: buffers correctly sized, parsed key is valid
unsafe {
ffi::init();
let mut ciphertext = [0u8; MlKem768PrivateKey::CIPHERTEXT_BYTES];
let mut shared_secret = [0u8; SHARED_SECRET_BYTES];

ffi::MLKEM768_encap(
ciphertext.as_mut_ptr(),
shared_secret.as_mut_ptr(),
&self.parsed,
);

(ciphertext, shared_secret)
}
}
}
Expand Down Expand Up @@ -439,39 +425,27 @@ impl MlKem1024PrivateKey {
pub const CIPHERTEXT_BYTES: usize = ffi::MLKEM1024_CIPHERTEXT_BYTES as usize;

/// Generate a new key pair.
#[must_use]
fn generate() -> (Box<MlKem1024PublicKey>, Box<MlKem1024PrivateKey>) {
fn generate() -> Result<(Box<MlKem1024PublicKey>, Box<MlKem1024PrivateKey>), ErrorStack> {
// SAFETY: all buffers are out parameters, correctly sized
unsafe {
ffi::init();
let mut public_key_bytes: MaybeUninit<[u8; MlKem1024PublicKey::PUBLIC_KEY_BYTES]> =
MaybeUninit::uninit();
let mut seed: MaybeUninit<MlKemPrivateKeySeed> = MaybeUninit::uninit();
let mut bytes = [0; MlKem1024PublicKey::PUBLIC_KEY_BYTES];
let mut seed = [0; PRIVATE_KEY_SEED_BYTES];
let mut expanded: MaybeUninit<ffi::MLKEM1024_private_key> = MaybeUninit::uninit();

ffi::MLKEM1024_generate_key(
public_key_bytes.as_mut_ptr().cast(),
seed.as_mut_ptr().cast(),
bytes.as_mut_ptr().cast(),
seed.as_mut_ptr(),
expanded.as_mut_ptr(),
);

let bytes = public_key_bytes.assume_init();

// Parse the public key bytes to get the parsed struct
let mut cbs = cbs_init(&bytes);
let mut parsed: MaybeUninit<ffi::MLKEM1024_public_key> = MaybeUninit::uninit();
ffi::MLKEM1024_parse_public_key(parsed.as_mut_ptr(), &mut cbs);

(
Box::new(MlKem1024PublicKey {
bytes,
parsed: parsed.assume_init(),
}),
Ok((
Box::new(MlKem1024PublicKey::from_slice(&bytes)?),
Box::new(MlKem1024PrivateKey {
seed: seed.assume_init(),
seed,
expanded: expanded.assume_init(),
}),
)
))
}
}

Expand Down Expand Up @@ -607,25 +581,19 @@ impl MlKem1024PublicKey {
}

/// Encapsulate: returns (ciphertext, shared_secret).
fn encapsulate(
fn encapsulate_into(
&self,
) -> (
[u8; MlKem1024PrivateKey::CIPHERTEXT_BYTES],
[u8; SHARED_SECRET_BYTES],
ciphertext: &mut [u8; MlKem1024PrivateKey::CIPHERTEXT_BYTES],
shared_secret: &mut [u8; SHARED_SECRET_BYTES],
) {
// SAFETY: buffers correctly sized, parsed key is valid
unsafe {
ffi::init();
let mut ciphertext = [0u8; MlKem1024PrivateKey::CIPHERTEXT_BYTES];
let mut shared_secret = [0u8; SHARED_SECRET_BYTES];

ffi::MLKEM1024_encap(
ciphertext.as_mut_ptr(),
shared_secret.as_mut_ptr(),
&self.parsed,
);

(ciphertext, shared_secret)
}
}
}
Expand All @@ -649,24 +617,28 @@ mod tests {

#[test]
fn roundtrip() {
let (pk, sk) = <$priv>::generate();
let (ct, ss1) = pk.encapsulate();
let (pk, sk) = <$priv>::generate().unwrap();
let mut ct = [0; _];
let mut ss1 = [0; _];
pk.encapsulate_into(&mut ct, &mut ss1);
let ss2 = sk.decapsulate(&ct);
assert_eq!(ss1, ss2);
}

#[test]
fn seed_roundtrip() {
let (pk, sk) = <$priv>::generate();
let (pk, sk) = <$priv>::generate().unwrap();
let sk2 = <$priv>::from_seed(&sk.seed).unwrap();
let (ct, ss1) = pk.encapsulate();
let mut ct = [0; _];
let mut ss1 = [0; _];
pk.encapsulate_into(&mut ct, &mut ss1);
let ss2 = sk2.decapsulate(&ct);
assert_eq!(ss1, ss2);
}

#[test]
fn derive_pubkey() {
let (pk, sk) = <$priv>::generate();
let (pk, sk) = <$priv>::generate().unwrap();
assert_eq!(pk.bytes, sk.public_key().unwrap().bytes);
}

Expand All @@ -678,14 +650,14 @@ mod tests {

#[test]
fn from_slice_roundtrip() {
let (pk, _) = <$priv>::generate();
let (pk, _) = <$priv>::generate().unwrap();
let pk2 = <$pub>::from_slice(&pk.bytes).unwrap();
assert_eq!(pk.bytes, pk2.bytes);
}

#[test]
fn implicit_rejection() {
let (_, sk) = <$priv>::generate();
let (_, sk) = <$priv>::generate().unwrap();
let bad_ct = [0x42u8; $ct_len];
// bad ciphertext still "works", just returns deterministic garbage
let ss1 = sk.decapsulate(&bad_ct);
Expand All @@ -695,7 +667,7 @@ mod tests {

#[test]
fn debug_redacts_seed() {
let (_, sk) = <$priv>::generate();
let (_, sk) = <$priv>::generate().unwrap();
let dbg = format!("{:?}", sk);
assert!(dbg.contains("redacted"));
}
Expand Down
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