Fix NPE when testing passphrase for stripped secret keys

Fixes #2173

Author: vanitasvitae

pg/src/main/java/org/bouncycastle/openpgp/api/OpenPGPKey.java

@@ -404,6 +404,7 @@ private void sanitizeProtectionMode()
 
         /**
          * Return true if the provided passphrase is correct.
+         * Note: This method will always return false for stripped secret keys.
          *
          * @param passphrase passphrase
          * @return true if the passphrase is correct
@@ -418,7 +419,7 @@ public boolean isPassphraseCorrect(char[] passphrase)
             try
             {
                 OpenPGPPrivateKey privateKey = unlock(passphrase);
-                return privateKey.unlockedKey != null;
+                return privateKey != null && privateKey.unlockedKey != null;
             }
             catch (PGPException e)
             {

pg/src/test/java/org/bouncycastle/openpgp/api/test/StrippedOpenPGPKeyTest.java

@@ -0,0 +1,53 @@
+package org.bouncycastle.openpgp.api.test;
+
+import org.bouncycastle.openpgp.PGPException;
+import org.bouncycastle.openpgp.api.OpenPGPApi;
+import org.bouncycastle.openpgp.api.OpenPGPKey;
+import org.bouncycastle.openpgp.api.OpenPGPKeyReader;
+
+import java.io.IOException;
+
+public class StrippedOpenPGPKeyTest
+        extends APITest
+{
+
+    @Override
+    protected void performTestWith(OpenPGPApi api)
+            throws PGPException, IOException
+    {
+        // Adapted test case from https://github.com/bcgit/bc-java/issues/2173
+        // Credit for test vectors to @agrahn
+        OpenPGPKeyReader reader = api.readKeyOrCertificate();
+        OpenPGPKey strippedKey = reader.parseKey(
+                "-----BEGIN PGP PRIVATE KEY BLOCK-----\n\n" +
+                        "lDsEaNz9VhYJKwYBBAHaRw8BAQdANvkQp6G9vVPUtxHplmw44lclTAm2vSqREnfi\n" +
+                        "bsqmDDP/AGUAR05VAbQfQm9iIFVzZXIgPGJvYi51c2VyQGV4YW1wbGUub3JnPoiT\n" +
+                        "BBMWCgA7FiEE81kLNGDerGMA7okHMcFP0Qqg/SwFAmjc/VYCGwEFCwkIBwICIgIG\n" +
+                        "FQoJCAsCBBYCAwECHgcCF4AACgkQMcFP0Qqg/Szv3AEA5Q0S6UrHI6YC9IqCV86Z\n" +
+                        "xF7zegeUJiTGfbIMmp+7qk4BAIJBZyfpsutfdnLBmXMQmPPvdlfNZ0H781sm4vq4\n" +
+                        "1KkFnIsEaNz9pRIKKwYBBAGXVQEFAQEHQLilfhrcbzI6XI7a+HbOfqNj/9cwZk8s\n" +
+                        "O4H/4IMhY7ZZAwEIB/4HAwIpPDPOpRpcw//ZZTsMuT5ZRDGnSA+3i34NWnhv50ex\n" +
+                        "yf51MgrvY+E3NaE9ObFfvEJILF8kub206yaQRbHWPrj7fU1C+DKJ9AbDcXZmzu/U\n" +
+                        "iHgEGBYKACAWIQTzWQs0YN6sYwDuiQcxwU/RCqD9LAUCaNz9pQIbDAAKCRAxwU/R\n" +
+                        "CqD9LCNSAP9v7GminBOFV8XkMsL4T+0P0woGjTZxUrYKKVR98NhXswEAhDfkQh0n\n" +
+                        "IyhOyHwzLuoGJ31M7a1rtB44tcJNtnP6XQQ=\n" +
+                        "=jquc\n" +
+                        "-----END PGP PRIVATE KEY BLOCK-----\n");
+
+        OpenPGPKey.OpenPGPSecretKey secKey = strippedKey.getPrimarySecretKey();
+
+        boolean isCorrect = secKey.isPassphraseCorrect(("12345678").toCharArray());
+        isFalse("Expected false when checking passphrase of stripped secret key", isCorrect);
+    }
+
+    @Override
+    public String getName()
+    {
+        return "StrippedOpenPGPKeyTest";
+    }
+
+    public static void main(String[] args)
+    {
+        runTest(new StrippedOpenPGPKeyTest());
+    }
+}