8281628: KeyAgreement : generateSecret intermittently not resetting

src/java.base/share/classes/com/sun/crypto/provider/DHKeyAgreement.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2022, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -334,6 +334,8 @@ protected int engineGenerateSecret(byte[] sharedSecret, int offset)
         } else {
             // Array too short, pad it w/ leading 0s
             if (secret.length < expectedLen) {
+                Arrays.fill(sharedSecret, offset,
+                        offset + (expectedLen - secret.length), (byte)0);
                 System.arraycopy(secret, 0, sharedSecret,
                     offset + (expectedLen - secret.length),
                     secret.length);

test/jdk/com/sun/crypto/provider/KeyAgreement/DHKeyAgreementPadding.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8281628
+ * @library /test/lib
+ * @summary ensure padding bytes are always added when generated secret
+ *      is smaller than buffer size.
+ */
+
+import javax.crypto.KeyAgreement;
+import java.security.KeyPair;
+import java.security.KeyPairGenerator;
+import java.util.Arrays;
+
+public class DHKeyAgreementPadding {
+
+    public static void main(String[] args) throws Exception {
+
+        byte[] aliceSecret = new byte[80];
+        byte[] bobSecret = new byte[80];
+
+        KeyAgreement alice = KeyAgreement.getInstance("DiffieHellman");
+        KeyAgreement bob = KeyAgreement.getInstance("DiffieHellman");
+
+        // The probability of an error is 0.2% or 1/500. Try more times.
+        for (int i = 0; i < 5000; i++) {
+            KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("DiffieHellman");
+            keyPairGen.initialize(512);
+            KeyPair aliceKeyPair = keyPairGen.generateKeyPair();
+            KeyPair bobKeyPair = keyPairGen.generateKeyPair();
+
+            // Different stale data
+            Arrays.fill(aliceSecret, (byte)'a');
+            Arrays.fill(bobSecret, (byte)'b');
+
+            alice.init(aliceKeyPair.getPrivate());
+            alice.doPhase(bobKeyPair.getPublic(), true);
+            int aliceLen = alice.generateSecret(aliceSecret, 0);
+
+            bob.init(bobKeyPair.getPrivate());
+            bob.doPhase(aliceKeyPair.getPublic(), true);
+            int bobLen = bob.generateSecret(bobSecret, 0);
+
+            if (!Arrays.equals(aliceSecret, 0, aliceLen, bobSecret, 0, bobLen)) {
+                System.out.println(bytesToHex(aliceSecret));
+                System.out.println(bytesToHex(bobSecret));
+                throw new RuntimeException("Different secrets observed at runs #" + i);
+            }
+        }
+    }
+    public static String bytesToHex(byte[] in) {
+        final StringBuilder builder = new StringBuilder();
+        for(byte b : in) {
+            builder.append(String.format("%02x", b)+":");
+        }
+        return builder.toString();
+    }
+}