Zeroize a copy of the card user PIN in the YubiKey decryptor factories, not the provider's array

Author: Arpan0995

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

@@ -14,6 +14,8 @@ public interface KeyPassphraseProvider
      * Return the passphrase for the given key.
      * This callback is only fired, if the key is locked and a passphrase is required to unlock it.
      * Returning null means, that the passphrase is not available.
+     * The returned array remains owned by the provider; a caller that needs to zeroize the
+     * passphrase after use must clone it first.
      *
      * @param key the locked (sub-)key.
      * @return passphrase or null

pgsc/src/main/java/org/bouncycastle/openpgp/smartcard/yubikey/operator/bc/BcYubikeyPublicKeyDataDecryptorFactory.java

@@ -224,13 +224,13 @@ private static boolean isSupportedCurve(String curveName)
     }
 
     /**
-     * Fetch the card's user PIN. The returned array is the caller's to zeroize once the card has
-     * verified it.
+     * Fetch the card's user PIN. A defensive copy of the provider's array is returned, so
+     * the copy is the caller's to zeroize once the card has verified it.
      */
     private char[] requireUserPin()
         throws KeyPassphraseException
     {
-        char[] pin = userPinProvider.getKeyPassword(getSecretKey());
+        char[] pin = Arrays.clone(userPinProvider.getKeyPassword(getSecretKey()));
         if (pin == null || pin.length == 0)
         {
             throw new KeyPassphraseException(getSecretKey(), new IllegalStateException("PIN required."));

pgsc/src/main/java/org/bouncycastle/openpgp/smartcard/yubikey/operator/jcajce/JceYubikeyPublicKeyDataDecryptorFactoryBuilder.java

@@ -173,11 +173,15 @@ private static boolean isSupportedCurve(String curveName)
             || "curve25519".equals(curveName);
     }
 
+    /**
+     * Fetch the card's user PIN. A defensive copy of the provider's array is returned, so
+     * the copy is the caller's to zeroize once the card has verified it.
+     */
     private char[] requireUserPin(KeyPassphraseProvider userPinProvider,
                                   OpenPGPKey.OpenPGPSecretKey key)
             throws KeyPassphraseException
     {
-        char[] pin = userPinProvider.getKeyPassword(key);
+        char[] pin = Arrays.clone(userPinProvider.getKeyPassword(key));
         if (pin == null || pin.length == 0)
         {
             throw new KeyPassphraseException(key, new IllegalStateException("PIN required."));

pgsc/src/test/java/org/bouncycastle/openpgp/smartcard/simulator/SimulatorTests.java

@@ -6,6 +6,7 @@
 import org.bouncycastle.openpgp.smartcard.test.AnonymousRecipientSmartCardDecryptionTest;
 import org.bouncycastle.openpgp.smartcard.test.SmartCardMessageDecryptionTest;
 import org.bouncycastle.openpgp.smartcard.test.SmartCardTestProperties;
+import org.bouncycastle.openpgp.smartcard.test.SmartCardUserPinOwnershipTest;
 import org.bouncycastle.openpgp.smartcard.test.UnrelatedSmartCardMessageDecryptionTest;
 import org.bouncycastle.util.test.SimpleTestResult;
 
@@ -25,6 +26,7 @@ public void testSimulatorSmartCard()
                         new SmartCardMessageDecryptionTest(m, p),
                         new AnonymousRecipientSmartCardDecryptionTest(m, p),
                         new UnrelatedSmartCardMessageDecryptionTest(m, p),
+                        new SmartCardUserPinOwnershipTest(m, p),
                         new SimulatorSmartCardTest(m, p)
                 };
 

pgsc/src/test/java/org/bouncycastle/openpgp/smartcard/test/SmartCardUserPinOwnershipTest.java

@@ -0,0 +1,320 @@
+package org.bouncycastle.openpgp.smartcard.test;
+
+import org.bouncycastle.bcpg.PublicKeyAlgorithmTags;
+import org.bouncycastle.bcpg.PublicKeyEncSessionPacket;
+import org.bouncycastle.crypto.InvalidCipherTextException;
+import org.bouncycastle.crypto.params.AsymmetricKeyParameter;
+import org.bouncycastle.openpgp.PGPException;
+import org.bouncycastle.openpgp.api.KeyPairGeneratorCallback;
+import org.bouncycastle.openpgp.api.KeyPassphraseProvider;
+import org.bouncycastle.openpgp.api.OpenPGPKey;
+import org.bouncycastle.openpgp.api.OpenPGPMessageInputStream;
+import org.bouncycastle.openpgp.api.OpenPGPMessageOutputStream;
+import org.bouncycastle.openpgp.operator.PGPKeyPairGenerator;
+import org.bouncycastle.openpgp.operator.PublicKeyDataDecryptorFactory;
+import org.bouncycastle.openpgp.smartcard.OpenPGPSmartCard;
+import org.bouncycastle.openpgp.smartcard.OpenPGPSmartCardManager;
+import org.bouncycastle.openpgp.smartcard.card.CardException;
+import org.bouncycastle.openpgp.smartcard.simulator.SimulatorOpenPGPSmartCard;
+import org.bouncycastle.openpgp.smartcard.simulator.SimulatorSmartCardBackend;
+import org.bouncycastle.openpgp.smartcard.yubikey.YubikeySmartCardBackend;
+import org.bouncycastle.openpgp.smartcard.yubikey.YubikeyTestInstanceProvider;
+import org.bouncycastle.openpgp.smartcard.yubikey.YubikeyTestProperties;
+import org.bouncycastle.openpgp.smartcard.yubikey.operator.bc.BcYubikeyPublicKeyDataDecryptorFactory;
+import org.bouncycastle.openpgp.smartcard.yubikey.operator.jcajce.JceYubikeyPublicKeyDataDecryptorFactoryBuilder;
+import org.bouncycastle.util.Arrays;
+import org.bouncycastle.util.io.Streams;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * A card user PIN fetched from a {@link KeyPassphraseProvider} stays owned by the provider.
+ * <p>
+ * Both {@link KeyPassphraseProvider} implementations BC ships hand out the array the application
+ * registered rather than a copy of it - {@code DefaultKeyPassphraseProvider} returns the
+ * {@code char[]} held in its cache, and the anonymous provider inside {@code OpenPGPApi.editKey}
+ * returns the caller's array verbatim - and every other consumer of
+ * {@link KeyPassphraseProvider#getKeyPassword} borrows the array and leaves it alone. The two
+ * YubiKey decryptor factories instead zeroized what they were handed, in a finally block after
+ * every private-key operation, so the first decryption destroyed the application's PIN: the next
+ * private-key operation presented an all-zero PIN to the card, which fails and costs a PIN retry.
+ * They now clear a copy of their own, which is the rule {@code ECJPAKEParticipant} and
+ * {@code JPAKEParticipant} state for a password they mean to clear.
+ * <p>
+ * The two factory cases need no token. The PIN handling brackets the card call - the PIN is fetched
+ * before the session is opened and cleared in a finally block after it - so driving a factory with
+ * no card exercises that handling in full, and only the card operation in between fails. Each case
+ * asserts the PIN really was fetched, so it cannot pass by failing ahead of the fetch.
+ * <p>
+ * The simulator case then locks the borrowing convention on the backend that runs with no hardware
+ * present: it unlocks the key it holds through the {@link KeyPassphraseProvider} it is handed, so a
+ * PIN is presented on every private-key operation as it is on a real card.
+ */
+public class SmartCardUserPinOwnershipTest
+        extends AbstractOpenPGPSmartCardTest
+{
+    public SmartCardUserPinOwnershipTest(OpenPGPSmartCardManager manager,
+                                        SmartCardTestProperties properties)
+    {
+        super(manager, properties);
+    }
+
+    @Override
+    public String getName()
+    {
+        return "SmartCardUserPinOwnershipTest";
+    }
+
+    @Override
+    public void performTest()
+            throws Exception
+    {
+        testPinSurvivesTwoConsecutiveDecryptions();
+        testBcYubikeyFactoryBorrowsProvidersPin();
+        testJceYubikeyFactoryBorrowsProvidersPin();
+    }
+
+    /**
+     * Decrypt two messages in a row against one cached PIN array, the shape an application gets from
+     * {@code OpenPGPMessageProcessor} for free: the PIN it registers is cached and handed to the
+     * card backend on every private-key operation, so a backend that zeroized it would destroy the
+     * application's PIN during the first message and present zeros during the second.
+     */
+    private void testPinSurvivesTwoConsecutiveDecryptions()
+            throws PGPException, IOException, CardException
+    {
+        OpenPGPSmartCard card = manager.findSmartCard(properties.getSerialNumber());
+        // -DM System.out.println
+        System.out.println("Test user PIN ownership over two messages on " + card.getCardType() + " " + card.getVersion() + " (" + card.getBackend().getName() + ")");
+
+        char[] expectedPin = properties.getUserPin();
+        char[] applicationPin = properties.getUserPin();
+
+        OpenPGPKey softwareKey = keyOnCard(card, expectedPin);
+        OpenPGPKey externalKey = toExternalKey(softwareKey, null);
+
+        isTrue("the stripped key must be marked external",
+                externalKey.getSecretKey(externalKey.getEncryptionKeys().get(0))
+                        .getPGPSecretKey().isExternalKey());
+
+        RecordingPinProvider pinProvider = new RecordingPinProvider(applicationPin);
+
+        for (int i = 1; i <= 2; i++)
+        {
+            byte[] plaintext = ("Message " + i + " to a card-held key.\n").getBytes(StandardCharsets.UTF_8);
+
+            isTrue("message " + i + ": decrypted plaintext mismatch",
+                    Arrays.areEqual(plaintext, decrypt(externalKey, pinProvider, encrypt(softwareKey, plaintext))));
+            isTrue("message " + i + ": the application's PIN buffer must be intact after decryption",
+                    Arrays.areEqual(expectedPin, applicationPin));
+        }
+
+        isEquals("the card must be presented the PIN once per message", 2, pinProvider.presentations.size());
+        for (int i = 0; i != pinProvider.presentations.size(); i++)
+        {
+            isTrue("presentation " + (i + 1) + " must carry the real PIN rather than a cleared buffer",
+                    Arrays.areEqual(expectedPin, pinProvider.presentations.get(i)));
+        }
+    }
+
+    private void testBcYubikeyFactoryBorrowsProvidersPin()
+            throws PGPException, InvalidCipherTextException
+    {
+        // -DM System.out.println
+        System.out.println("Test BcYubikeyPublicKeyDataDecryptorFactory borrows the PIN it is given");
+
+        char[] expectedPin = properties.getUserPin();
+        char[] applicationPin = properties.getUserPin();
+        RecordingPinProvider pinProvider = new RecordingPinProvider(applicationPin);
+
+        BcYubikeyPublicKeyDataDecryptorFactory factory =
+                new BcYubikeyPublicKeyDataDecryptorFactory(externalDecryptionKey(), null, pinProvider);
+
+        try
+        {
+            factory.getExternalKeyCryptoCallback().decryptRSA(
+                    PublicKeyAlgorithmTags.RSA_GENERAL, new byte[]{(byte)0xAA}, (AsymmetricKeyParameter)null);
+            fail("a private-key operation with no card present must fail");
+        }
+        catch (RuntimeException e)
+        {
+            // expected: there is no card to open a session on
+        }
+
+        implTestPinBorrowed("BcYubikeyPublicKeyDataDecryptorFactory", pinProvider, expectedPin, applicationPin);
+    }
+
+    private void testJceYubikeyFactoryBorrowsProvidersPin()
+            throws PGPException
+    {
+        // -DM System.out.println
+        System.out.println("Test JceYubikeyPublicKeyDataDecryptorFactoryBuilder borrows the PIN it is given");
+
+        char[] expectedPin = properties.getUserPin();
+        char[] applicationPin = properties.getUserPin();
+        RecordingPinProvider pinProvider = new RecordingPinProvider(applicationPin);
+
+        PublicKeyDataDecryptorFactory factory =
+                new JceYubikeyPublicKeyDataDecryptorFactoryBuilder(null, pinProvider).build(externalDecryptionKey());
+
+        try
+        {
+            factory.recoverSessionData(PublicKeyAlgorithmTags.RSA_GENERAL,
+                    new byte[][]{new byte[]{0, 8, (byte)0xAA}}, PublicKeyEncSessionPacket.VERSION_3);
+            fail("a private-key operation with no card present must fail");
+        }
+        catch (RuntimeException e)
+        {
+            // expected: there is no card to open a session on
+        }
+
+        implTestPinBorrowed("JceYubikeyPublicKeyDataDecryptorFactoryBuilder", pinProvider, expectedPin, applicationPin);
+    }
+
+    private void implTestPinBorrowed(String label,
+                                     RecordingPinProvider pinProvider,
+                                     char[] expectedPin,
+                                     char[] applicationPin)
+    {
+        isEquals(label + ": the PIN must be fetched from the provider exactly once",
+                1, pinProvider.presentations.size());
+        isTrue(label + ": the PIN handed to the card must be the registered one",
+                Arrays.areEqual(expectedPin, pinProvider.presentations.get(0)));
+        isTrue(label + ": the provider's PIN array must survive the operation",
+                Arrays.areEqual(expectedPin, applicationPin));
+    }
+
+    /**
+     * Generate a key protected with the card's user PIN, move its decryption key onto the card and
+     * return the software copy the message is encrypted to.
+     */
+    private OpenPGPKey keyOnCard(OpenPGPSmartCard card, char[] userPin)
+            throws PGPException, CardException
+    {
+        card.reset();
+
+        // build(char[]) clears the array it is given, so it gets a copy
+        OpenPGPKey softwareKey = api.generateKey(4)
+                .withPrimaryKey((KeyPairGeneratorCallback)PGPKeyPairGenerator::generateEd25519KeyPair)
+                .addEncryptionSubkey((KeyPairGeneratorCallback)PGPKeyPairGenerator::generateX25519KeyPair)
+                .build(Arrays.clone(userPin));
+
+        OpenPGPKey.OpenPGPSecretKey decryptionKey =
+                softwareKey.getSecretKey(softwareKey.getEncryptionKeys().get(0));
+        card.uploadDecryptionKey(decryptionKey.unlock(Arrays.clone(userPin)), properties.getAdminPin());
+
+        return softwareKey;
+    }
+
+    /**
+     * An externally-backed decryption key, which is all either factory needs to be built. No card is
+     * involved: the private key material is simply absent.
+     */
+    private OpenPGPKey.OpenPGPSecretKey externalDecryptionKey()
+            throws PGPException
+    {
+        OpenPGPKey softwareKey = api.generateKey(4)
+                .withPrimaryKey((KeyPairGeneratorCallback)PGPKeyPairGenerator::generateEd25519KeyPair)
+                .addEncryptionSubkey((KeyPairGeneratorCallback)PGPKeyPairGenerator::generateX25519KeyPair)
+                .build();
+        OpenPGPKey externalKey = toExternalKey(softwareKey, null);
+
+        return externalKey.getSecretKey(externalKey.getEncryptionKeys().get(0));
+    }
+
+    private byte[] encrypt(OpenPGPKey recipient, byte[] plaintext)
+            throws PGPException, IOException
+    {
+        ByteArrayOutputStream bOut = new ByteArrayOutputStream();
+        OpenPGPMessageOutputStream mOut = api.signAndOrEncryptMessage()
+                .addEncryptionCertificate(recipient.toCertificate())
+                .open(bOut);
+        mOut.write(plaintext);
+        mOut.close();
+
+        return bOut.toByteArray();
+    }
+
+    private byte[] decrypt(OpenPGPKey externalKey, KeyPassphraseProvider pinProvider, byte[] message)
+            throws PGPException, IOException
+    {
+        OpenPGPMessageInputStream mIn = api.decryptAndOrVerifyMessage()
+                .addDecryptionKey(externalKey)
+                .setMissingOpenPGPKeyPassphraseProvider(pinProvider)
+                .addPublicKeyDataDecryptorFactoryProvider(manager)
+                .process(new ByteArrayInputStream(message));
+        ByteArrayOutputStream plainOut = new ByteArrayOutputStream();
+        Streams.pipeAll(mIn, plainOut);
+        mIn.close();
+
+        return plainOut.toByteArray();
+    }
+
+    /**
+     * Hands out one cached array on every call, as
+     * {@code KeyPassphraseProvider.DefaultKeyPassphraseProvider} does, and records a snapshot of what
+     * each call returned so the PIN the card was presented can be checked afterwards.
+     */
+    private static class RecordingPinProvider
+            implements KeyPassphraseProvider
+    {
+        final char[] pin;
+        final List<char[]> presentations = new ArrayList<char[]>();
+
+        RecordingPinProvider(char[] pin)
+        {
+            this.pin = pin;
+        }
+
+        public char[] getKeyPassword(OpenPGPKey.OpenPGPSecretKey key)
+        {
+            presentations.add(Arrays.clone(pin));
+            return pin;
+        }
+    }
+
+    public static void main(String[] args)
+        throws CardException
+    {
+        SmartCardTestProperties p;
+        OpenPGPSmartCardManager m;
+
+        // BCYK
+        try
+        {
+            p = new YubikeyTestProperties();
+            m = YubikeyTestInstanceProvider.prepareOneYubikeySmartCardManager(p, YubikeySmartCardBackend.bcImpl());
+            runTest(new SmartCardUserPinOwnershipTest(m, p));
+        }
+        catch (YubikeyTestInstanceProvider.YubikeySetupException e)
+        {
+            // -DM System.out.println
+            System.out.println("Skipping run of SmartCardUserPinOwnershipTest on BC Yubikey.");
+        }
+
+        // JCYK
+        try
+        {
+            p = new YubikeyTestProperties();
+            m = YubikeyTestInstanceProvider.prepareOneYubikeySmartCardManager(p, YubikeySmartCardBackend.jceImpl());
+            runTest(new SmartCardUserPinOwnershipTest(m, p));
+        }
+        catch (YubikeyTestInstanceProvider.YubikeySetupException e)
+        {
+            // -DM System.out.println
+            System.out.println("Skipping run of SmartCardUserPinOwnershipTest on JCE Yubikey.");
+        }
+
+
+        SimulatorSmartCardBackend sim = new SimulatorSmartCardBackend();
+        sim.addSmartCard(new SimulatorOpenPGPSmartCard(sim, 1312));
+        m = new OpenPGPSmartCardManager().addBackend(sim);
+
+        runTest(new SmartCardUserPinOwnershipTest(m, new SmartCardTestProperties(1312)));
+    }
+}