Fix exchange with keys that had Q automatically computed (#11309)

fixes #10790
closes #10864
closes #11218

docs/development/test-vectors.rst

@@ -224,6 +224,10 @@ Key exchange
 * ``vectors/cryptoraphy_vectors/asymmetric/ECDH/brainpool.txt`` contains
   Brainpool vectors from :rfc:`7027`.
 
+* ``vectors/cryptography_vectors/asymmetric/DH/dhpub_cryptography_old.pem``
+  contains a Diffie-Hellman public key generated with a previous version of
+  ``cryptography``.
+
 X.509
 ~~~~~
 

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

@@ -114,13 +114,7 @@ pub fn parse_public_key(
             let pub_key = openssl::bn::BigNum::from_slice(pub_key_int.as_bytes())?;
             let dh = dh.set_public_key(pub_key)?;
 
-            cfg_if::cfg_if! {
-                if #[cfg(CRYPTOGRAPHY_IS_LIBRESSL)] {
-                    Ok(openssl::pkey::PKey::from_dh(dh)?)
-                } else {
-                    Ok(openssl::pkey::PKey::from_dhx(dh)?)
-                }
-            }
+            Ok(openssl::pkey::PKey::from_dh(dh)?)
         }
         #[cfg(not(CRYPTOGRAPHY_IS_BORINGSSL))]
         AlgorithmParameters::DhKeyAgreement(dh_params) => {

src/rust/src/backend/dh.rs

@@ -70,23 +70,6 @@ pub(crate) fn public_key_from_pkey(
     }
 }
 
-#[cfg(not(CRYPTOGRAPHY_IS_BORINGSSL))]
-fn pkey_from_dh<T: openssl::pkey::HasParams>(
-    dh: openssl::dh::Dh<T>,
-) -> CryptographyResult<openssl::pkey::PKey<T>> {
-    cfg_if::cfg_if! {
-        if #[cfg(CRYPTOGRAPHY_IS_LIBRESSL)] {
-            Ok(openssl::pkey::PKey::from_dh(dh)?)
-        } else {
-            if dh.prime_q().is_some() {
-                Ok(openssl::pkey::PKey::from_dhx(dh)?)
-            } else {
-                Ok(openssl::pkey::PKey::from_dh(dh)?)
-            }
-        }
-    }
-}
-
 #[pyo3::pyfunction]
 #[pyo3(signature = (data, backend=None))]
 fn from_der_parameters(
@@ -214,7 +197,8 @@ impl DHPrivateKey {
         let orig_dh = self.pkey.dh().unwrap();
         let dh = clone_dh(&orig_dh)?;
 
-        let pkey = pkey_from_dh(dh.set_public_key(orig_dh.public_key().to_owned()?)?)?;
+        let pkey =
+            openssl::pkey::PKey::from_dh(dh.set_public_key(orig_dh.public_key().to_owned()?)?)?;
 
         Ok(DHPublicKey { pkey })
     }
@@ -322,7 +306,7 @@ impl DHParameters {
     fn generate_private_key(&self) -> CryptographyResult<DHPrivateKey> {
         let dh = clone_dh(&self.dh)?.generate_key()?;
         Ok(DHPrivateKey {
-            pkey: pkey_from_dh(dh)?,
+            pkey: openssl::pkey::PKey::from_dh(dh)?,
         })
     }
 
@@ -435,7 +419,7 @@ impl DHPrivateNumbers {
             ));
         }
 
-        let pkey = pkey_from_dh(dh)?;
+        let pkey = openssl::pkey::PKey::from_dh(dh)?;
         Ok(DHPrivateKey { pkey })
     }
 
@@ -478,7 +462,7 @@ impl DHPublicNumbers {
 
         let pub_key = utils::py_int_to_bn(py, self.y.bind(py))?;
 
-        let pkey = pkey_from_dh(dh.set_public_key(pub_key)?)?;
+        let pkey = openssl::pkey::PKey::from_dh(dh.set_public_key(pub_key)?)?;
 
         Ok(DHPublicKey { pkey })
     }

tests/hazmat/primitives/test_dh.py

@@ -441,6 +441,16 @@ class TestDH:
         assert int.from_bytes(symkey1, "big") == int(vector["z"], 16)
         assert int.from_bytes(symkey2, "big") == int(vector["z"], 16)
 
+    def test_exchange_old_key(self, backend):
+        k = load_vectors_from_file(
+            os.path.join("asymmetric", "DH", "dhpub_cryptography_old.pem"),
+            lambda f: serialization.load_pem_public_key(f.read()),
+            mode="rb",
+        )
+        assert isinstance(k, dh.DHPublicKey)
+        # Ensure this doesn't raise.
+        k.parameters().generate_private_key().exchange(k)
+
     def test_public_key_equality(self, backend):
         key_bytes = load_vectors_from_file(
             os.path.join("asymmetric", "DH", "dhpub.pem"),

vectors/cryptography_vectors/asymmetric/DH/dhpub_cryptography_old.pem

@@ -0,0 +1,15 @@
+-----BEGIN PUBLIC KEY-----
+MIICJTCCARcGCSqGSIb3DQEDATCCAQgCggEBAP//////////yQ/aoiFowjTExmKL
+gNwc0SkCTgiKZ8x0Agu+pjsTmyJRSgh5jjQE3e+VGbPNOkMbMCsKbfJfFDdP4TVt
+bVHCReSFtXZiXn7G9ExC6aY37WsL/1y29Aa37e44a/taiZ+lrp8kEXxLH+ZJKGZR
+7ORbPcIAfLihY78FmNpINhxV05ppFj+o/STPX4NlXSPco62WHGLzViCFUrue1SkH
+cJaWbWcMNU5KvJgE8XRsCMoYIXwykF5GLjbOO+OedywYDoY DmyeDouwHoo+1xV3w
+b0xSyd4ry/aVWBcYOZVJfOqVauUV0iYYmPoFEBVyjlqKrKpo//////////8CAQID
+ggEGAAKCAQEAoely6vSHw+/Q3zGYLaJj7eeQkfd25K8SvtC+FMY9D7jwS4g71pyr
+U3FJ98Fi45Wdksh+d4u7U089trF5Xbgui29bZ0HcQZtfHEEz0Mh69tkipCm2/QIj
+6eDlo6sPk9hhhvgg4MMGiWKhCtHrub3x1FHdmf7KjOhrGeb5apiudo7blGFzGhZ3
+NFnbff+ArVNd+rdVmSoZn0aMhXRConlDu/44IYe5/24VLl7G+BzZlIZO4P2M83fd
+mBOvR13cmYssQjEFTbaZVQvQHa3t0+aywfdCgsXGmTTK6QDCBP8D+vf1bmhEswzs
+oYn1GLtJ3VyYyMBPDBomd2ctchZgTzsX1w==
+-----END PUBLIC KEY-----
+