--- a/src/jdk.crypto.ec/share/classes/sun/security/ec/XDHKeyAgreement.java	Fri Jul 13 15:44:54 2018 +0200
+++ b/src/jdk.crypto.ec/share/classes/sun/security/ec/XDHKeyAgreement.java	Fri Jul 13 10:42:30 2018 -0400
@@ -69,13 +69,15 @@
 
         initImpl(key);
 
-        // the private key parameters must match params
-        XECParameters xecParams = XECParameters.get(
-            InvalidAlgorithmParameterException::new, params);
-        if (!xecParams.oidEquals(this.ops.getParameters())) {
-            throw new InvalidKeyException(
-                "Incorrect private key parameters"
-            );
+        // the private key parameters must match params, if present
+        if (params != null) {
+            XECParameters xecParams = XECParameters.get(
+                InvalidAlgorithmParameterException::new, params);
+            if (!xecParams.oidEquals(this.ops.getParameters())) {
+                throw new InvalidKeyException(
+                    "Incorrect private key parameters"
+                );
+            }
         }
     }
 
@@ -171,7 +173,9 @@
             throw new IllegalStateException("Not initialized correctly");
         }
 
-        return secret.clone();
+        byte[] result = secret;
+        secret = null;
+        return result;
     }
 
     @Override
@@ -189,7 +193,8 @@
         }
 
         System.arraycopy(this.secret, 0, sharedSecret, offset, secretLen);
-        return secret.length;
+        secret = null;
+        return secretLen;
     }
 
     @Override

--- a/test/jdk/sun/security/ec/xec/TestXDH.java	Fri Jul 13 15:44:54 2018 +0200
+++ b/test/jdk/sun/security/ec/xec/TestXDH.java	Fri Jul 13 10:42:30 2018 -0400
@@ -23,7 +23,7 @@
 
 /*
  * @test
- * @bug 8171277
+ * @bug 8171277 8206915
  * @summary Test XDH key agreement
  * @library /test/lib
  * @build jdk.test.lib.Convert
@@ -66,15 +66,17 @@
         throws Exception {
 
         KeyPairGenerator kpg = KeyPairGenerator.getInstance(name);
+        AlgorithmParameterSpec paramSpec = null;
         if (param instanceof Integer) {
             kpg.initialize((Integer) param);
         } else if (param instanceof String) {
-            kpg.initialize(new NamedParameterSpec((String) param));
+            paramSpec = new NamedParameterSpec((String) param);
+            kpg.initialize(paramSpec);
         }
         KeyPair kp = kpg.generateKeyPair();
 
         KeyAgreement ka = KeyAgreement.getInstance(name);
-        ka.init(kp.getPrivate());
+        ka.init(kp.getPrivate(), paramSpec);
         ka.doPhase(kp.getPublic(), true);
 
         byte[] secret = ka.generateSecret();
@@ -96,6 +98,16 @@
             throw new RuntimeException("Arrays not equal");
         }
 
+        // make sure generateSecret() resets the state to after init()
+        try {
+            ka.generateSecret();
+            throw new RuntimeException("generateSecret does not reset state");
+        } catch (IllegalStateException ex) {
+            // do nothing---this is expected
+        }
+        ka.doPhase(pubKey, true);
+        ka.generateSecret();
+
         // test with XDH key specs
         XECPublicKeySpec xdhPublic =
             kf.getKeySpec(kp.getPublic(), XECPublicKeySpec.class);