Skip PKCS#8 round-trip when extracting ML-DSA/ML-KEM seeds on BoringSSL

src/rust/cryptography-key-parsing/src/pkcs8.rs

@@ -48,14 +48,13 @@ pub enum MlDsaPrivateKey {
 
 /// Extract the ML-KEM seed from a private key.
 ///
-/// For BoringSSL/AWS-LC, round-trips through PKCS#8 encoding to extract the
-/// seed. AWS-LC's `raw_private_key()` returns the 2400-byte expanded key, not
-/// the seed; since AWS-LC 1.72.0, `private_key_to_pkcs8()` produces RFC 9935
-/// seed-format PKCS#8 when the key was created from a seed. BoringSSL's
-/// private key serialization also emits RFC 9935 seed-format PKCS#8.
+/// For BoringSSL and OpenSSL 3.5+, calls the library's seed extraction API
+/// directly (`EVP_PKEY_get_private_seed` / `PKey::seed_into`).
 ///
-/// For vanilla OpenSSL 3.5+, calls `PKey::seed_into` to read the seed
-/// directly, avoiding the PKCS#8 round-trip.
+/// For AWS-LC, round-trips through PKCS#8 encoding because
+/// `raw_private_key()` returns the 2400-byte expanded key. Since AWS-LC
+/// 1.72.0, `private_key_to_pkcs8()` produces RFC 9935 seed-format PKCS#8
+/// when the key was created from a seed.
 #[cfg(any(
     CRYPTOGRAPHY_IS_BORINGSSL,
     CRYPTOGRAPHY_IS_AWSLC,
@@ -65,11 +64,11 @@ pub fn mlkem_seed_from_pkey(
     pkey: &openssl::pkey::PKeyRef<openssl::pkey::Private>,
 ) -> Result<MlKemPrivateKey, openssl::error::ErrorStack> {
     cfg_if::cfg_if! {
-        if #[cfg(any(CRYPTOGRAPHY_IS_BORINGSSL, CRYPTOGRAPHY_IS_AWSLC))] {
+        if #[cfg(CRYPTOGRAPHY_IS_AWSLC)] {
             let pkcs8_der = pkey.private_key_to_pkcs8()?;
             let pki = asn1::parse_single::<PrivateKeyInfo<'_>>(&pkcs8_der).unwrap();
             Ok(asn1::parse_single::<MlKemPrivateKey>(pki.private_key).unwrap())
-        } else if #[cfg(CRYPTOGRAPHY_OPENSSL_350_OR_GREATER)] {
+        } else {
             let seed = cryptography_openssl::mlkem::mlkem_seed_raw(pkey)?;
             Ok(MlKemPrivateKey::Seed(seed))
         }
@@ -78,13 +77,12 @@ pub fn mlkem_seed_from_pkey(
 
 /// Extract the 32-byte ML-DSA seed from a private key.
 ///
-/// For BoringSSL/AWS-LC, round-trips through PKCS#8 encoding to extract the
-/// seed (AWS-LC's `raw_private_key()` returns the expanded key, not the seed:
-/// https://github.com/aws/aws-lc/issues/3072).
+/// For BoringSSL and OpenSSL 3.5+, calls the library's seed extraction API
+/// directly (`EVP_PKEY_get_private_seed` / `PKey::seed_into`).
 ///
-/// For vanilla OpenSSL 3.5+, calls `PKey::seed_into` to read the seed
-/// directly, since OpenSSL 3.5's PKCS#8 inner encoding differs from
-/// BoringSSL/AWS-LC.
+/// For AWS-LC, round-trips through PKCS#8 encoding because
+/// `raw_private_key()` returns the expanded key, not the seed
+/// (https://github.com/aws/aws-lc/issues/3072).
 #[cfg(any(
     CRYPTOGRAPHY_IS_BORINGSSL,
     CRYPTOGRAPHY_IS_AWSLC,
@@ -94,11 +92,11 @@ pub fn mldsa_seed_from_pkey(
     pkey: &openssl::pkey::PKeyRef<openssl::pkey::Private>,
 ) -> Result<MlDsaPrivateKey, openssl::error::ErrorStack> {
     cfg_if::cfg_if! {
-        if #[cfg(any(CRYPTOGRAPHY_IS_BORINGSSL, CRYPTOGRAPHY_IS_AWSLC))] {
+        if #[cfg(CRYPTOGRAPHY_IS_AWSLC)] {
             let pkcs8_der = pkey.private_key_to_pkcs8()?;
             let pki = asn1::parse_single::<PrivateKeyInfo<'_>>(&pkcs8_der).unwrap();
             Ok(asn1::parse_single::<MlDsaPrivateKey>(pki.private_key).unwrap())
-        } else if #[cfg(CRYPTOGRAPHY_OPENSSL_350_OR_GREATER)] {
+        } else {
             let seed = cryptography_openssl::mldsa::mldsa_seed_raw(pkey)?;
             Ok(MlDsaPrivateKey::Seed(seed))
         }

src/rust/cryptography-openssl/src/mldsa.rs

@@ -206,12 +206,27 @@ extern "C" {
 ///
 /// Avoids the PKCS#8 round-trip that vanilla OpenSSL 3.5 encodes
 /// differently from BoringSSL/AWS-LC.
-#[cfg(CRYPTOGRAPHY_OPENSSL_350_OR_GREATER)]
+#[cfg(any(CRYPTOGRAPHY_IS_BORINGSSL, CRYPTOGRAPHY_OPENSSL_350_OR_GREATER))]
 pub fn mldsa_seed_raw(
     pkey: &openssl::pkey::PKeyRef<openssl::pkey::Private>,
 ) -> OpenSSLResult<[u8; 32]> {
     let mut seed = [0u8; 32];
-    pkey.seed_into(&mut seed)?;
+    cfg_if::cfg_if! {
+        if #[cfg(CRYPTOGRAPHY_IS_BORINGSSL)] {
+            let mut seed_len = seed.len();
+            // SAFETY: pkey is a valid EVP_PKEY and seed is a 32-byte buffer.
+            unsafe {
+                cvt(ffi::EVP_PKEY_get_private_seed(
+                    pkey.as_ptr(),
+                    seed.as_mut_ptr(),
+                    &mut seed_len,
+                ))?;
+            }
+            assert_eq!(seed_len, 32);
+        } else if #[cfg(CRYPTOGRAPHY_OPENSSL_350_OR_GREATER)] {
+            pkey.seed_into(&mut seed)?;
+        }
+    }
     Ok(seed)
 }
 

src/rust/cryptography-openssl/src/mlkem.rs

@@ -3,6 +3,8 @@
 // for complete details.
 
 use foreign_types_shared::ForeignType;
+#[cfg(CRYPTOGRAPHY_IS_BORINGSSL)]
+use foreign_types_shared::ForeignTypeRef;
 use openssl_sys as ffi;
 #[cfg(CRYPTOGRAPHY_IS_AWSLC)]
 use std::os::raw::c_int;
@@ -121,12 +123,27 @@ extern "C" {
 ///
 /// Avoids the PKCS#8 round-trip that vanilla OpenSSL 3.5 encodes
 /// differently from BoringSSL/AWS-LC.
-#[cfg(CRYPTOGRAPHY_OPENSSL_350_OR_GREATER)]
+#[cfg(any(CRYPTOGRAPHY_IS_BORINGSSL, CRYPTOGRAPHY_OPENSSL_350_OR_GREATER))]
 pub fn mlkem_seed_raw(
     pkey: &openssl::pkey::PKeyRef<openssl::pkey::Private>,
 ) -> OpenSSLResult<[u8; 64]> {
     let mut seed = [0u8; 64];
-    pkey.seed_into(&mut seed)?;
+    cfg_if::cfg_if! {
+        if #[cfg(CRYPTOGRAPHY_IS_BORINGSSL)] {
+            let mut seed_len = seed.len();
+            // SAFETY: pkey is a valid EVP_PKEY and seed is a 64-byte buffer.
+            unsafe {
+                cvt(ffi::EVP_PKEY_get_private_seed(
+                    pkey.as_ptr(),
+                    seed.as_mut_ptr(),
+                    &mut seed_len,
+                ))?;
+            }
+            assert_eq!(seed_len, 64);
+        } else if #[cfg(CRYPTOGRAPHY_OPENSSL_350_OR_GREATER)] {
+            pkey.seed_into(&mut seed)?;
+        }
+    }
     Ok(seed)
 }