honour the pass phrase cache TTL by running a timer and removing expired cached pass phrases

src/org/thialfihar/android/apg/Apg.java

@@ -41,6 +41,7 @@ import java.util.Date;
 import java.util.GregorianCalendar;
 import java.util.HashMap;
 import java.util.Iterator;
+import java.util.Map;
 import java.util.Vector;
 import java.util.regex.Pattern;
 
@@ -293,9 +294,26 @@ public class Apg {
         if (cpp == null) {
             return null;
         }
+        // set it again to reset the cache life cycle
+        setCachedPassPhrase(realId, cpp.passPhrase);
         return cpp.passPhrase;
     }
 
+    public static void cleanUpCache(int ttl) {
+        long now = new Date().getTime();
+
+        Vector<Long> oldKeys = new Vector<Long>();
+        for (Map.Entry<Long, CachedPassPhrase> pair : mPassPhraseCache.entrySet()) {
+            if ((now - pair.getValue().timestamp) >= 1000 * ttl) {
+                oldKeys.add(pair.getKey());
+            }
+        }
+
+        for (long keyId : oldKeys) {
+            mPassPhraseCache.remove(keyId);
+        }
+    }
+
     public static PGPSecretKey createKey(Context context,
                                          int algorithmChoice, int keySize, String passPhrase,
                                          PGPSecretKey masterKey)
@@ -1266,7 +1284,7 @@ public class Apg {
 
         PGPSignatureGenerator signatureGenerator = null;
         progress.setProgress(R.string.progress_preparingStreams, 5, 100);
-        // encryptFile and compress input file content
+        // encrypt and compress input file content
         PGPEncryptedDataGenerator cPk =
                 new PGPEncryptedDataGenerator(symmetricAlgorithm, true, new SecureRandom(),
                                               new BouncyCastleProvider());

src/org/thialfihar/android/apg/BaseActivity.java

@@ -17,6 +17,8 @@
 package org.thialfihar.android.apg;
 
 import java.io.File;
+import java.util.Timer;
+import java.util.TimerTask;
 
 import org.bouncycastle2.bcpg.HashAlgorithmTags;
 import org.bouncycastle2.openpgp.PGPEncryptedData;
@@ -50,6 +52,8 @@ public class BaseActivity extends Activity
     private String mDeleteFile = null;
     protected static SharedPreferences mPreferences = null;
 
+    private static Timer mCacheTimer = new Timer();
+
     private Handler mHandler = new Handler() {
         @Override
         public void handleMessage(Message msg) {
@@ -65,6 +69,29 @@ public class BaseActivity extends Activity
             mPreferences = getPreferences(MODE_PRIVATE);
         }
         Apg.initialize(this);
+        if (mCacheTimer == null) {
+            setPassPhraseCacheTimer();
+        }
+    }
+
+    private void setPassPhraseCacheTimer() {
+        if (mCacheTimer != null) {
+            mCacheTimer.cancel();
+            mCacheTimer = null;
+        }
+        int ttl = getPassPhraseCacheTtl();
+        if (ttl == 0) {
+            // no timer needed
+            return;
+        }
+        // check every ttl/2 seconds, which shouldn't be heavy on the device (even if ttl = 15),
+        // and makes sure the longest a pass phrase survives int the cache is 1.5 * ttl
+        mCacheTimer = new Timer();
+        mCacheTimer.scheduleAtFixedRate(new TimerTask() {
+            public void run() {
+                Apg.cleanUpCache(BaseActivity.this.getPassPhraseCacheTtl());
+            }
+        }, 0, ttl * 1000 / 2);
     }
 
     @Override
@@ -98,7 +125,6 @@ public class BaseActivity extends Activity
 
     @Override
     protected Dialog onCreateDialog(int id) {
-
         // in case it is a progress dialog
         mProgressDialog = new ProgressDialog(this);
         mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
@@ -354,14 +380,16 @@ public class BaseActivity extends Activity
         return mSecretKeyId;
     }
 
-    public int getPassPhraseCache() {
-        return mPreferences.getInt(Constants.pref.pass_phrase_cache_length, 300);
+    public int getPassPhraseCacheTtl() {
+        return mPreferences.getInt(Constants.pref.pass_phrase_cache_ttl, 300);
     }
 
-    public void setPassPhraseCache(int value) {
+    public void setPassPhraseCacheTtl(int value) {
         SharedPreferences.Editor editor = mPreferences.edit();
-        editor.putInt(Constants.pref.pass_phrase_cache_length, value);
+        editor.putInt(Constants.pref.pass_phrase_cache_ttl, value);
         editor.commit();
+
+        setPassPhraseCacheTimer();
     }
 
     public int getDefaultEncryptionAlgorithm() {

src/org/thialfihar/android/apg/Constants.java

@@ -28,6 +28,6 @@ public final class Constants {
         public static final String default_encryption_algorithm = "defaultEncryptionAlgorithm";
         public static final String default_hash_algorithm = "defaultHashAlgorithm";
         public static final String default_ascii_armour = "defaultAsciiArmour";
-        public static final String pass_phrase_cache_length = "passPhraseCacheLength";
+        public static final String pass_phrase_cache_ttl = "passPhraseCacheTtl";
     }
 }

src/org/thialfihar/android/apg/PreferencesActivity.java

@@ -55,7 +55,7 @@ public class PreferencesActivity extends BaseActivity {
         adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
         mPassPhraseCache.setAdapter(adapter);
 
-        int passPhraseCache = getPassPhraseCache();
+        int passPhraseCache = getPassPhraseCacheTtl();
         for (int i = 0; i < choices.length; ++i) {
             if (choices[i].getId() == passPhraseCache) {
                 mPassPhraseCache.setSelection(i);
@@ -66,7 +66,7 @@ public class PreferencesActivity extends BaseActivity {
         mPassPhraseCache.setOnItemSelectedListener(new OnItemSelectedListener() {
             @Override
             public void onItemSelected(AdapterView<?> adapter, View view, int index, long id) {
-                setPassPhraseCache(((Choice) mPassPhraseCache.getSelectedItem()).getId());
+                setPassPhraseCacheTtl(((Choice) mPassPhraseCache.getSelectedItem()).getId());
             }
 
             @Override