introduce CachingDataDecryptorFactory towards cached session keys

this commit introduces the CachingDataDecryptorFactory, which wraps
a DataDecryptorFactory but supports caching of decrypted session keys.

this change also gets rid of runtimeexception based control flow in
PgpDecryptVerify.

7 files changed, 145 insertions, 319 deletions

diff --git a/OpenKeychain/src/main/java/org/spongycastle/openpgp/operator/jcajce/CachingDataDecryptorFactory.java b/OpenKeychain/src/main/java/org/spongycastle/openpgp/operator/jcajce/CachingDataDecryptorFactory.java
new file mode 100644
index 000000000..d35f1d751
--- /dev/null
+++ b/OpenKeychain/src/main/java/org/spongycastle/openpgp/operator/jcajce/CachingDataDecryptorFactory.java
@@ -0,0 +1,76 @@
+/**
+ * Copyright (c) 2013-2014 Philipp Jakubeit, Signe Rüsch, Dominik Schürmann
+ *
+ * Licensed under the Bouncy Castle License (MIT license). See LICENSE file for details.
+ */
+
+package org.spongycastle.openpgp.operator.jcajce;
+
+import org.spongycastle.jcajce.util.NamedJcaJceHelper;
+import org.spongycastle.openpgp.PGPException;
+import org.spongycastle.openpgp.PGPPublicKeyEncryptedData;
+import org.spongycastle.openpgp.operator.PGPDataDecryptor;
+import org.spongycastle.openpgp.operator.PublicKeyDataDecryptorFactory;
+
+import java.nio.ByteBuffer;
+import java.util.Map;
+
+public class CachingDataDecryptorFactory implements PublicKeyDataDecryptorFactory
+{
+    private final PublicKeyDataDecryptorFactory mWrappedDecryptor;
+    private final Map<ByteBuffer, byte[]> mSessionKeyCache;
+
+    private OperatorHelper mOperatorHelper;
+
+    public CachingDataDecryptorFactory(String providerName,
+            final Map<ByteBuffer,byte[]> sessionKeyCache)
+    {
+        mWrappedDecryptor = null;
+        mSessionKeyCache = sessionKeyCache;
+
+        mOperatorHelper = new OperatorHelper(new NamedJcaJceHelper(providerName));
+    }
+
+    public CachingDataDecryptorFactory(PublicKeyDataDecryptorFactory wrapped,
+            final Map<ByteBuffer,byte[]> sessionKeyCache)
+    {
+        mWrappedDecryptor = wrapped;
+        mSessionKeyCache = sessionKeyCache;
+
+    }
+
+    public boolean hasCachedSessionData(PGPPublicKeyEncryptedData encData) throws PGPException {
+        ByteBuffer bi = ByteBuffer.wrap(encData.getSessionKey()[0]);
+        return mSessionKeyCache.containsKey(bi);
+    }
+
+    public Map<ByteBuffer, byte[]> getCachedSessionKeys() {
+        return mSessionKeyCache;
+    }
+
+    public boolean canDecrypt() {
+        return mWrappedDecryptor != null;
+    }
+
+    @Override
+    public byte[] recoverSessionData(int keyAlgorithm, byte[][] secKeyData) throws PGPException {
+        ByteBuffer bi = ByteBuffer.wrap(secKeyData[0]);  // encoded MPI
+        if (mSessionKeyCache.containsKey(bi)) {
+            return mSessionKeyCache.get(bi);
+        }
+
+        byte[] sessionData = mWrappedDecryptor.recoverSessionData(keyAlgorithm, secKeyData);
+        mSessionKeyCache.put(bi, sessionData);
+        return sessionData;
+    }
+
+    @Override
+    public PGPDataDecryptor createDataDecryptor(boolean withIntegrityPacket, int encAlgorithm, byte[] key)
+            throws PGPException {
+        if (mWrappedDecryptor != null) {
+            return mWrappedDecryptor.createDataDecryptor(withIntegrityPacket, encAlgorithm, key);
+        }
+        return mOperatorHelper.createDataDecryptor(withIntegrityPacket, encAlgorithm, key);
+    }
+
+}
diff --git a/OpenKeychain/src/main/java/org/spongycastle/openpgp/operator/jcajce/NfcSyncPublicKeyDataDecryptorFactoryBuilder.java b/OpenKeychain/src/main/java/org/spongycastle/openpgp/operator/jcajce/NfcSyncPublicKeyDataDecryptorFactoryBuilder.java
deleted file mode 100644
index 067bb3e19..000000000
--- a/OpenKeychain/src/main/java/org/spongycastle/openpgp/operator/jcajce/NfcSyncPublicKeyDataDecryptorFactoryBuilder.java
+++ /dev/null
@@ -1,278 +0,0 @@
-/**
- * Copyright (c) 2013-2014 Philipp Jakubeit, Signe Rüsch, Dominik Schürmann
- *
- * Licensed under the Bouncy Castle License (MIT license). See LICENSE file for details.
- */
-
-package org.spongycastle.openpgp.operator.jcajce;
-
-import org.spongycastle.bcpg.PublicKeyAlgorithmTags;
-import org.spongycastle.jcajce.util.DefaultJcaJceHelper;
-import org.spongycastle.jcajce.util.NamedJcaJceHelper;
-import org.spongycastle.jcajce.util.ProviderJcaJceHelper;
-import org.spongycastle.openpgp.PGPException;
-import org.spongycastle.openpgp.PGPPublicKey;
-import org.spongycastle.openpgp.operator.PGPDataDecryptor;
-import org.spongycastle.openpgp.operator.PublicKeyDataDecryptorFactory;
-
-import java.nio.ByteBuffer;
-import java.security.Provider;
-import java.util.Map;
-
-
-/**
- * This class is based on JcePublicKeyDataDecryptorFactoryBuilder
- *
- */
-public class NfcSyncPublicKeyDataDecryptorFactoryBuilder
-{
-    private OperatorHelper helper = new OperatorHelper(new DefaultJcaJceHelper());
-    private OperatorHelper contentHelper = new OperatorHelper(new DefaultJcaJceHelper());
-    private JcaPGPKeyConverter keyConverter = new JcaPGPKeyConverter();
-//    private JcaPGPDigestCalculatorProviderBuilder digestCalculatorProviderBuilder = new JcaPGPDigestCalculatorProviderBuilder();
-//    private JcaKeyFingerprintCalculator fingerprintCalculator = new JcaKeyFingerprintCalculator();
-
-    public static class NfcInteractionNeeded extends RuntimeException
-    {
-        public byte[] encryptedSessionKey;
-
-        public NfcInteractionNeeded(byte[] encryptedSessionKey)
-        {
-            super("NFC interaction required!");
-            this.encryptedSessionKey = encryptedSessionKey;
-        }
-    }
-
-    public NfcSyncPublicKeyDataDecryptorFactoryBuilder()
-    {
-    }
-
-    /**
-     * Set the provider object to use for creating cryptographic primitives in the resulting factory the builder produces.
-     *
-     * @param provider  provider object for cryptographic primitives.
-     * @return  the current builder.
-     */
-    public NfcSyncPublicKeyDataDecryptorFactoryBuilder setProvider(Provider provider)
-    {
-        this.helper = new OperatorHelper(new ProviderJcaJceHelper(provider));
-        keyConverter.setProvider(provider);
-        this.contentHelper = helper;
-
-        return this;
-    }
-
-    /**
-     * Set the provider name to use for creating cryptographic primitives in the resulting factory the builder produces.
-     *
-     * @param providerName  the name of the provider to reference for cryptographic primitives.
-     * @return  the current builder.
-     */
-    public NfcSyncPublicKeyDataDecryptorFactoryBuilder setProvider(String providerName)
-    {
-        this.helper = new OperatorHelper(new NamedJcaJceHelper(providerName));
-        keyConverter.setProvider(providerName);
-        this.contentHelper = helper;
-
-        return this;
-    }
-
-    public NfcSyncPublicKeyDataDecryptorFactoryBuilder setContentProvider(Provider provider)
-    {
-        this.contentHelper = new OperatorHelper(new ProviderJcaJceHelper(provider));
-
-        return this;
-    }
-
-    public NfcSyncPublicKeyDataDecryptorFactoryBuilder setContentProvider(String providerName)
-    {
-        this.contentHelper = new OperatorHelper(new NamedJcaJceHelper(providerName));
-
-        return this;
-    }
-
-    public PublicKeyDataDecryptorFactory build(final Map<ByteBuffer,byte[]> nfcDecryptedMap) {
-        return new PublicKeyDataDecryptorFactory()
-        {
-            public byte[] recoverSessionData(int keyAlgorithm, byte[][] secKeyData)
-                    throws PGPException
-            {
-                if (keyAlgorithm == PublicKeyAlgorithmTags.ECDH)
-                {
-                    throw new PGPException("ECDH not supported!");
-                }
-
-                return decryptSessionData(keyAlgorithm, secKeyData, nfcDecryptedMap);
-            }
-
-            public PGPDataDecryptor createDataDecryptor(boolean withIntegrityPacket, int encAlgorithm, byte[] key)
-                    throws PGPException
-            {
-                return contentHelper.createDataDecryptor(withIntegrityPacket, encAlgorithm, key);
-            }
-        };
-    }
-
-//    public PublicKeyDataDecryptorFactory build(final PrivateKey privKey)
-//    {
-//        return new PublicKeyDataDecryptorFactory()
-//        {
-//            public byte[] recoverSessionData(int keyAlgorithm, byte[][] secKeyData)
-//                    throws PGPException
-//            {
-//                if (keyAlgorithm == PublicKeyAlgorithmTags.ECDH)
-//                {
-//                    throw new PGPException("ECDH requires use of PGPPrivateKey for decryption");
-//                }
-//                return decryptSessionData(keyAlgorithm, privKey, secKeyData);
-//            }
-//
-//            public PGPDataDecryptor createDataDecryptor(boolean withIntegrityPacket, int encAlgorithm, byte[] key)
-//                    throws PGPException
-//            {
-//                return contentHelper.createDataDecryptor(withIntegrityPacket, encAlgorithm, key);
-//            }
-//        };
-//    }
-
-//    public PublicKeyDataDecryptorFactory build(final PGPPrivateKey privKey, final byte[] nfcDecrypted)
-//    {
-//        return new PublicKeyDataDecryptorFactory()
-//        {
-//            public byte[] recoverSessionData(int keyAlgorithm, byte[][] secKeyData)
-//                    throws PGPException
-//            {
-//                if (keyAlgorithm == PublicKeyAlgorithmTags.ECDH)
-//                {
-//                    return decryptSessionData(privKey.getPrivateKeyDataPacket(), privKey.getPublicKeyPacket(), secKeyData);
-//                }
-//
-//                return decryptSessionData(keyAlgorithm, keyConverter.getPrivateKey(privKey), secKeyData, nfcDecrypted);
-//            }
-//
-//            public PGPDataDecryptor createDataDecryptor(boolean withIntegrityPacket, int encAlgorithm, byte[] key)
-//                    throws PGPException
-//            {
-//                return contentHelper.createDataDecryptor(withIntegrityPacket, encAlgorithm, key);
-//            }
-//        };
-//    }
-
-//    private byte[] decryptSessionData(BCPGKey privateKeyPacket, PublicKeyPacket pubKeyData, byte[][] secKeyData)
-//            throws PGPException
-//    {
-//        ECDHPublicBCPGKey ecKey = (ECDHPublicBCPGKey)pubKeyData.getKey();
-//        X9ECParameters x9Params = NISTNamedCurves.getByOID(ecKey.getCurveOID());
-//
-//        byte[] enc = secKeyData[0];
-//
-//        int pLen = ((((enc[0] & 0xff) << 8) + (enc[1] & 0xff)) + 7) / 8;
-//        byte[] pEnc = new byte[pLen];
-//
-//        System.arraycopy(enc, 2, pEnc, 0, pLen);
-//
-//        byte[] keyEnc = new byte[enc[pLen + 2]];
-//
-//        System.arraycopy(enc, 2 + pLen + 1, keyEnc, 0, keyEnc.length);
-//
-//        Cipher c = helper.createKeyWrapper(ecKey.getSymmetricKeyAlgorithm());
-//
-//        ECPoint S = x9Params.getCurve().decodePoint(pEnc).multiply(((ECSecretBCPGKey)privateKeyPacket).getX()).normalize();
-//
-//        RFC6637KDFCalculator rfc6637KDFCalculator = new RFC6637KDFCalculator(digestCalculatorProviderBuilder.build().get(ecKey.getHashAlgorithm()), ecKey.getSymmetricKeyAlgorithm());
-//        Key key = new SecretKeySpec(rfc6637KDFCalculator.createKey(ecKey.getCurveOID(), S, fingerprintCalculator.calculateFingerprint(pubKeyData)), "AESWrap");
-//
-//        try
-//        {
-//            c.init(Cipher.UNWRAP_MODE, key);
-//
-//            Key paddedSessionKey = c.unwrap(keyEnc, "Session", Cipher.SECRET_KEY);
-//
-//            return PGPPad.unpadSessionData(paddedSessionKey.getEncoded());
-//        }
-//        catch (InvalidKeyException e)
-//        {
-//            throw new PGPException("error setting asymmetric cipher", e);
-//        }
-//        catch (NoSuchAlgorithmException e)
-//        {
-//            throw new PGPException("error setting asymmetric cipher", e);
-//        }
-//    }
-
-    private byte[] decryptSessionData(int keyAlgorithm, byte[][] secKeyData,
-            Map<ByteBuffer,byte[]> nfcDecryptedMap)
-        throws PGPException
-    {
-//        Cipher c1 = helper.createPublicKeyCipher(keyAlgorithm);
-//
-//        try
-//        {
-//            c1.init(Cipher.DECRYPT_MODE, privKey);
-//        }
-//        catch (InvalidKeyException e)
-//        {
-//            throw new PGPException("error setting asymmetric cipher", e);
-//        }
-
-        if (keyAlgorithm == PGPPublicKey.RSA_ENCRYPT
-                || keyAlgorithm == PGPPublicKey.RSA_GENERAL)
-        {
-            ByteBuffer bi = ByteBuffer.wrap(secKeyData[0]);  // encoded MPI
-
-            if (nfcDecryptedMap.containsKey(bi)) {
-                return nfcDecryptedMap.get(bi);
-            } else {
-                // catch this when decryptSessionData() is executed and divert digest to card,
-                // when doing the operation again reuse nfcDecrypted
-                throw new NfcInteractionNeeded(bi.array());
-            }
-
-//            c1.update(bi, 2, bi.length - 2);
-        }
-        else
-        {
-            throw new PGPException("ElGamal not supported!");
-
-//            ElGamalKey k = (ElGamalKey)privKey;
-//            int size = (k.getParameters().getP().bitLength() + 7) / 8;
-//            byte[] tmp = new byte[size];
-//
-//            byte[] bi = secKeyData[0]; // encoded MPI
-//            if (bi.length - 2 > size)  // leading Zero? Shouldn't happen but...
-//            {
-//                c1.update(bi, 3, bi.length - 3);
-//            }
-//            else
-//            {
-//                System.arraycopy(bi, 2, tmp, tmp.length - (bi.length - 2), bi.length - 2);
-//                c1.update(tmp);
-//            }
-//
-//            bi = secKeyData[1];  // encoded MPI
-//            for (int i = 0; i != tmp.length; i++)
-//            {
-//                tmp[i] = 0;
-//            }
-//
-//            if (bi.length - 2 > size) // leading Zero? Shouldn't happen but...
-//            {
-//                c1.update(bi, 3, bi.length - 3);
-//            }
-//            else
-//            {
-//                System.arraycopy(bi, 2, tmp, tmp.length - (bi.length - 2), bi.length - 2);
-//                c1.update(tmp);
-//            }
-        }
-
-//        try
-//        {
-//            return c1.doFinal();
-//        }
-//        catch (Exception e)
-//        {
-//            throw new PGPException("exception decrypting session data", e);
-//        }
-    }
-}
diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/operations/results/DecryptVerifyResult.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/operations/results/DecryptVerifyResult.java
index ac571390a..25a86f137 100644
--- a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/operations/results/DecryptVerifyResult.java
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/operations/results/DecryptVerifyResult.java
@@ -22,6 +22,7 @@ import android.os.Parcel;
 
 import org.openintents.openpgp.OpenPgpMetadata;
 import org.openintents.openpgp.OpenPgpSignatureResult;
+import org.sufficientlysecure.keychain.service.input.CryptoInputParcel;
 import org.sufficientlysecure.keychain.service.input.RequiredInputParcel;
 import org.sufficientlysecure.keychain.util.Passphrase;
 
@@ -36,6 +37,8 @@ public class DecryptVerifyResult extends InputPendingResult {
     // https://tools.ietf.org/html/rfc4880#page56
     String mCharset;
 
+    CryptoInputParcel mCachedCryptoInputParcel;
+
     byte[] mOutputBytes;
 
     public DecryptVerifyResult(int result, OperationLog log) {
@@ -50,6 +53,7 @@ public class DecryptVerifyResult extends InputPendingResult {
         super(source);
         mSignatureResult = source.readParcelable(OpenPgpSignatureResult.class.getClassLoader());
         mDecryptMetadata = source.readParcelable(OpenPgpMetadata.class.getClassLoader());
+        mCachedCryptoInputParcel = source.readParcelable(CryptoInputParcel.class.getClassLoader());
     }
 
 
@@ -65,6 +69,14 @@ public class DecryptVerifyResult extends InputPendingResult {
         mSignatureResult = signatureResult;
     }
 
+    public CryptoInputParcel getCachedCryptoInputParcel() {
+        return mCachedCryptoInputParcel;
+    }
+
+    public void setCachedCryptoInputParcel(CryptoInputParcel cachedCryptoInputParcel) {
+        mCachedCryptoInputParcel = cachedCryptoInputParcel;
+    }
+
     public OpenPgpMetadata getDecryptMetadata() {
         return mDecryptMetadata;
     }
@@ -97,6 +109,7 @@ public class DecryptVerifyResult extends InputPendingResult {
         super.writeToParcel(dest, flags);
         dest.writeParcelable(mSignatureResult, 0);
         dest.writeParcelable(mDecryptMetadata, 0);
+        dest.writeParcelable(mCachedCryptoInputParcel, 0);
     }
 
     public static final Creator<DecryptVerifyResult> CREATOR = new Creator<DecryptVerifyResult>() {
diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/CanonicalizedSecretKey.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/CanonicalizedSecretKey.java
index 17d342341..31a3925da 100644
--- a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/CanonicalizedSecretKey.java
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/CanonicalizedSecretKey.java
@@ -21,23 +21,18 @@ package org.sufficientlysecure.keychain.pgp;
 import org.spongycastle.bcpg.S2K;
 import org.spongycastle.openpgp.PGPException;
 import org.spongycastle.openpgp.PGPPrivateKey;
-import org.spongycastle.openpgp.PGPPublicKey;
-import org.spongycastle.openpgp.PGPPublicKeyRing;
 import org.spongycastle.openpgp.PGPSecretKey;
 import org.spongycastle.openpgp.PGPSignature;
 import org.spongycastle.openpgp.PGPSignatureGenerator;
 import org.spongycastle.openpgp.PGPSignatureSubpacketGenerator;
-import org.spongycastle.openpgp.PGPSignatureSubpacketVector;
-import org.spongycastle.openpgp.PGPUserAttributeSubpacketVector;
 import org.spongycastle.openpgp.operator.PBESecretKeyDecryptor;
 import org.spongycastle.openpgp.operator.PGPContentSignerBuilder;
-import org.spongycastle.openpgp.operator.PublicKeyDataDecryptorFactory;
+import org.spongycastle.openpgp.operator.jcajce.CachingDataDecryptorFactory;
 import org.spongycastle.openpgp.operator.jcajce.JcaPGPContentSignerBuilder;
 import org.spongycastle.openpgp.operator.jcajce.JcaPGPKeyConverter;
 import org.spongycastle.openpgp.operator.jcajce.JcePBESecretKeyDecryptorBuilder;
 import org.spongycastle.openpgp.operator.jcajce.JcePublicKeyDataDecryptorFactoryBuilder;
 import org.spongycastle.openpgp.operator.jcajce.NfcSyncPGPContentSignerBuilder;
-import org.spongycastle.openpgp.operator.jcajce.NfcSyncPublicKeyDataDecryptorFactoryBuilder;
 import org.sufficientlysecure.keychain.Constants;
 import org.sufficientlysecure.keychain.pgp.exception.PgpGeneralException;
 import org.sufficientlysecure.keychain.pgp.exception.PgpKeyNotFoundException;
@@ -51,7 +46,6 @@ import java.security.interfaces.RSAPrivateCrtKey;
 import java.util.ArrayList;
 import java.util.Date;
 import java.util.HashMap;
-import java.util.List;
 import java.util.Map;
 
 
@@ -270,19 +264,20 @@ public class CanonicalizedSecretKey extends CanonicalizedPublicKey {
         }
     }
 
-    public PublicKeyDataDecryptorFactory getDecryptorFactory(CryptoInputParcel cryptoInput) {
+    public CachingDataDecryptorFactory getCachingDecryptorFactory(CryptoInputParcel cryptoInput) {
         if (mPrivateKeyState == PRIVATE_KEY_STATE_LOCKED) {
             throw new PrivateKeyNotUnlockedException();
         }
 
         if (mPrivateKeyState == PRIVATE_KEY_STATE_DIVERT_TO_CARD) {
-            return new NfcSyncPublicKeyDataDecryptorFactoryBuilder()
-                    .setProvider(Constants.BOUNCY_CASTLE_PROVIDER_NAME).build(
-                            cryptoInput.getCryptoData()
-                    );
+            return new CachingDataDecryptorFactory(
+                    Constants.BOUNCY_CASTLE_PROVIDER_NAME,
+                    cryptoInput.getCryptoData());
         } else {
-            return new JcePublicKeyDataDecryptorFactoryBuilder()
-                    .setProvider(Constants.BOUNCY_CASTLE_PROVIDER_NAME).build(mPrivateKey);
+            return new CachingDataDecryptorFactory(
+                    new JcePublicKeyDataDecryptorFactoryBuilder()
+                            .setProvider(Constants.BOUNCY_CASTLE_PROVIDER_NAME).build(mPrivateKey),
+                    cryptoInput.getCryptoData());
         }
     }
 
diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/PgpDecryptVerify.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/PgpDecryptVerify.java
index 4382c9fae..235b0a671 100644
--- a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/PgpDecryptVerify.java
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/PgpDecryptVerify.java
@@ -24,6 +24,7 @@ import android.webkit.MimeTypeMap;
 import org.openintents.openpgp.OpenPgpMetadata;
 import org.openintents.openpgp.OpenPgpSignatureResult;
 import org.spongycastle.bcpg.ArmoredInputStream;
+import org.spongycastle.bcpg.PublicKeyEncSessionPacket;
 import org.spongycastle.openpgp.PGPCompressedData;
 import org.spongycastle.openpgp.PGPEncryptedData;
 import org.spongycastle.openpgp.PGPEncryptedDataList;
@@ -40,11 +41,10 @@ import org.spongycastle.openpgp.PGPUtil;
 import org.spongycastle.openpgp.jcajce.JcaPGPObjectFactory;
 import org.spongycastle.openpgp.operator.PBEDataDecryptorFactory;
 import org.spongycastle.openpgp.operator.PGPDigestCalculatorProvider;
-import org.spongycastle.openpgp.operator.PublicKeyDataDecryptorFactory;
+import org.spongycastle.openpgp.operator.jcajce.CachingDataDecryptorFactory;
 import org.spongycastle.openpgp.operator.jcajce.JcaPGPContentVerifierBuilderProvider;
 import org.spongycastle.openpgp.operator.jcajce.JcaPGPDigestCalculatorProviderBuilder;
 import org.spongycastle.openpgp.operator.jcajce.JcePBEDataDecryptorFactoryBuilder;
-import org.spongycastle.openpgp.operator.jcajce.NfcSyncPublicKeyDataDecryptorFactoryBuilder;
 import org.sufficientlysecure.keychain.Constants;
 import org.sufficientlysecure.keychain.R;
 import org.sufficientlysecure.keychain.operations.BaseOperation;
@@ -541,24 +541,33 @@ public class PgpDecryptVerify extends BaseOperation {
             currentProgress += 2;
             updateProgress(R.string.progress_preparing_streams, currentProgress, 100);
 
-            try {
-                PublicKeyDataDecryptorFactory decryptorFactory
-                        = secretEncryptionKey.getDecryptorFactory(cryptoInput);
-                try {
-                    clear = encryptedDataAsymmetric.getDataStream(decryptorFactory);
-                } catch (PGPKeyValidationException | ArrayIndexOutOfBoundsException e) {
-                    log.add(LogType.MSG_DC_ERROR_CORRUPT_DATA, indent + 1);
-                    return new DecryptVerifyResult(DecryptVerifyResult.RESULT_ERROR, log);
-                }
+            CachingDataDecryptorFactory decryptorFactory
+                    = secretEncryptionKey.getCachingDecryptorFactory(cryptoInput);
+
+            // special case: if the decryptor does not have a session key cached for this encrypted
+            // data, and can't actually decrypt on its own, return a pending intent
+            if (!decryptorFactory.canDecrypt()
+                    && !decryptorFactory.hasCachedSessionData(encryptedDataAsymmetric)) {
 
-                symmetricEncryptionAlgo = encryptedDataAsymmetric.getSymmetricAlgorithm(decryptorFactory);
-            } catch (NfcSyncPublicKeyDataDecryptorFactoryBuilder.NfcInteractionNeeded e) {
                 log.add(LogType.MSG_DC_PENDING_NFC, indent + 1);
                 return new DecryptVerifyResult(log, RequiredInputParcel.createNfcDecryptOperation(
                         secretEncryptionKey.getRing().getMasterKeyId(),
-                        secretEncryptionKey.getKeyId(), e.encryptedSessionKey
+                        secretEncryptionKey.getKeyId(), encryptedDataAsymmetric.getSessionKey()[0]
                 ));
+
             }
+
+            try {
+                clear = encryptedDataAsymmetric.getDataStream(decryptorFactory);
+            } catch (PGPKeyValidationException | ArrayIndexOutOfBoundsException e) {
+                log.add(LogType.MSG_DC_ERROR_CORRUPT_DATA, indent + 1);
+                return new DecryptVerifyResult(DecryptVerifyResult.RESULT_ERROR, log);
+            }
+
+            symmetricEncryptionAlgo = encryptedDataAsymmetric.getSymmetricAlgorithm(decryptorFactory);
+
+            cryptoInput.addCryptoData(decryptorFactory.getCachedSessionKeys());
+
             encryptedData = encryptedDataAsymmetric;
         } else {
             // there wasn't even any useful data
@@ -821,6 +830,7 @@ public class PgpDecryptVerify extends BaseOperation {
         // Return a positive result, with metadata and verification info
         DecryptVerifyResult result =
                 new DecryptVerifyResult(DecryptVerifyResult.RESULT_OK, log);
+        result.setCachedCryptoInputParcel(cryptoInput);
         result.setDecryptMetadata(metadata);
         result.setSignatureResult(signatureResultBuilder.build());
         result.setCharset(charset);
diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/service/input/CryptoInputParcel.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/service/input/CryptoInputParcel.java
index 3d1ccaca1..ee7caf2d8 100644
--- a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/service/input/CryptoInputParcel.java
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/service/input/CryptoInputParcel.java
@@ -97,8 +97,12 @@ public class CryptoInputParcel implements Parcelable {
         mCryptoData.put(ByteBuffer.wrap(hash), signedHash);
     }
 
+    public void addCryptoData(Map<ByteBuffer, byte[]> cachedSessionKeys) {
+        mCryptoData.putAll(cachedSessionKeys);
+    }
+
     public Map<ByteBuffer, byte[]> getCryptoData() {
-        return Collections.unmodifiableMap(mCryptoData);
+        return mCryptoData;
     }
 
     public Date getSignatureTime() {
@@ -138,4 +142,5 @@ public class CryptoInputParcel implements Parcelable {
         b.append("}");
         return b.toString();
     }
+
 }
diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/DecryptFilesFragment.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/DecryptFilesInputFragment.java
index 254b926d4..3f15376cb 100644
--- a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/DecryptFilesFragment.java
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/DecryptFilesInputFragment.java
@@ -48,7 +48,7 @@ import org.sufficientlysecure.keychain.util.Log;
 
 import java.io.File;
 
-public class DecryptFilesFragment extends DecryptFragment {
+public class DecryptFilesInputFragment extends DecryptFragment {
     public static final String ARG_URI = "uri";
     public static final String ARG_OPEN_DIRECTLY = "open_directly";
 
@@ -69,8 +69,8 @@ public class DecryptFilesFragment extends DecryptFragment {
     /**
      * Creates new instance of this fragment
      */
-    public static DecryptFilesFragment newInstance(Uri uri, boolean openDirectly) {
-        DecryptFilesFragment frag = new DecryptFilesFragment();
+    public static DecryptFilesInputFragment newInstance(Uri uri, boolean openDirectly) {
+        DecryptFilesInputFragment frag = new DecryptFilesInputFragment();
 
         Bundle args = new Bundle();
         args.putParcelable(ARG_URI, uri);
@@ -94,9 +94,9 @@ public class DecryptFilesFragment extends DecryptFragment {
         view.findViewById(R.id.decrypt_files_browse).setOnClickListener(new View.OnClickListener() {
             public void onClick(View v) {
                 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
-                    FileHelper.openDocument(DecryptFilesFragment.this, "*/*", REQUEST_CODE_INPUT);
+                    FileHelper.openDocument(DecryptFilesInputFragment.this, "*/*", REQUEST_CODE_INPUT);
                 } else {
-                    FileHelper.openFile(DecryptFilesFragment.this, mInputUri, "*/*",
+                    FileHelper.openFile(DecryptFilesInputFragment.this, mInputUri, "*/*",
                             REQUEST_CODE_INPUT);
                 }
             }
@@ -128,9 +128,9 @@ public class DecryptFilesFragment extends DecryptFragment {
         // should only come from args
         if (state.getBoolean(ARG_OPEN_DIRECTLY, false)) {
             if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
-                FileHelper.openDocument(DecryptFilesFragment.this, "*/*", REQUEST_CODE_INPUT);
+                FileHelper.openDocument(DecryptFilesInputFragment.this, "*/*", REQUEST_CODE_INPUT);
             } else {
-                FileHelper.openFile(DecryptFilesFragment.this, mInputUri, "*/*", REQUEST_CODE_INPUT);
+                FileHelper.openFile(DecryptFilesInputFragment.this, mInputUri, "*/*", REQUEST_CODE_INPUT);
             }
         }
     }
@@ -180,6 +180,10 @@ public class DecryptFilesFragment extends DecryptFragment {
         }
     }
 
+    private void displayMetadata(DecryptVerifyResult result) {
+
+    }
+
     private void startDecrypt() {
         mCurrentCryptoOperation = KeychainIntentService.ACTION_DECRYPT_VERIFY;
         cryptoOperation(new CryptoInputParcel());
@@ -233,18 +237,19 @@ public class DecryptFilesFragment extends DecryptFragment {
                     // get returned data bundle
                     Bundle returnData = message.getData();
 
-                    DecryptVerifyResult pgpResult =
+                    DecryptVerifyResult result =
                             returnData.getParcelable(DecryptVerifyResult.EXTRA_RESULT);
 
-                    if (pgpResult.success()) {
+                    if (result.success()) {
                         switch (mCurrentCryptoOperation) {
                             case KeychainIntentService.ACTION_DECRYPT_METADATA: {
-                                askForOutputFilename(pgpResult.getDecryptMetadata().getFilename());
+                                displayMetadata(result);
+                                // askForOutputFilename(pgpResult.getDecryptMetadata().getFilename());
                                 break;
                             }
                             case KeychainIntentService.ACTION_DECRYPT_VERIFY: {
                                 // display signature result in activity
-                                loadVerifyResult(pgpResult);
+                                loadVerifyResult(result);
 
                                 if (mDeleteAfter.isChecked()) {
                                     // Create and show dialog to delete original file
@@ -269,7 +274,7 @@ public class DecryptFilesFragment extends DecryptFragment {
                             }
                         }
                     }
-                    pgpResult.createNotify(getActivity()).show(DecryptFilesFragment.this);
+                    result.createNotify(getActivity()).show(DecryptFilesInputFragment.this);
                 }
 
             }