diff --git a/F-Droid/src/javax/jmdns/impl/FDroidServiceInfo.java b/F-Droid/src/javax/jmdns/impl/FDroidServiceInfo.java
index c4fba32f3..111354994 100644
--- a/F-Droid/src/javax/jmdns/impl/FDroidServiceInfo.java
+++ b/F-Droid/src/javax/jmdns/impl/FDroidServiceInfo.java
@@ -2,6 +2,7 @@ package javax.jmdns.impl;
 
 import android.os.Parcel;
 import android.os.Parcelable;
+import android.text.TextUtils;
 
 import java.net.Inet4Address;
 import java.net.Inet6Address;
@@ -21,8 +22,21 @@ public class FDroidServiceInfo extends ServiceInfoImpl implements Parcelable {
         super(info);
     }
 
+    /**
+     * Return the fingerprint of the signing key, or {@code null} if it is not set.
+     */
     public String getFingerprint() {
-        return getPropertyString("fingerprint");
+        // getPropertyString() will return "true" if the value is a zero-length byte array
+        // so we just do a custom version using getPropertyBytes()
+        byte[] data = getPropertyBytes("fingerprint");
+        if (data == null || data.length == 0) {
+            return null;
+        }
+        String fingerprint = this.readUTF(data, 0, data.length);
+        if (TextUtils.isEmpty(fingerprint)) {
+            return null;
+        }
+        return fingerprint;
     }
 
     public String getRepoAddress() {
diff --git a/F-Droid/src/org/fdroid/fdroid/RepoUpdater.java b/F-Droid/src/org/fdroid/fdroid/RepoUpdater.java
index 17b964e52..b23d28f7e 100644
--- a/F-Droid/src/org/fdroid/fdroid/RepoUpdater.java
+++ b/F-Droid/src/org/fdroid/fdroid/RepoUpdater.java
@@ -36,6 +36,14 @@ import javax.xml.parsers.ParserConfigurationException;
 import javax.xml.parsers.SAXParser;
 import javax.xml.parsers.SAXParserFactory;
 
+/**
+ * Handles getting the index metadata for an app repo, then verifying the
+ * signature on the index metdata, implementing as a JAR signature.
+ * <p/>
+ * <b>WARNING</b>: this class is the central piece of the entire security model of
+ * FDroid!  Avoid modifying it when possible, if you absolutely must, be very,
+ * very careful with the changes that you are making!
+ */
 public class RepoUpdater {
 
     private static final String TAG = "RepoUpdater";
@@ -280,7 +288,8 @@ public class RepoUpdater {
          * actually in the index.jar itself.  If no fingerprint, just store the
          * signing certificate */
         boolean trustNewSigningCertificate = false;
-        if (TextUtils.isEmpty(repo.fingerprint)) {
+        // If the fingerprint has never been set, it will be null (never "" or something else)
+        if (repo.fingerprint == null) {
             // no info to check things are valid, so just Trust On First Use
             trustNewSigningCertificate = true;
         } else {
@@ -290,7 +299,8 @@ public class RepoUpdater {
                     && repo.fingerprint.equalsIgnoreCase(fingerprintFromJar)) {
                 trustNewSigningCertificate = true;
             } else {
-                throw new UpdateException(repo, "Supplied certificate fingerprint does not match!");
+                throw new UpdateException(repo, "Supplied certificate fingerprint does not match: '"
+                            + repo.fingerprint + "' '" + fingerprintFromIndexXml + "' '" + fingerprintFromJar + "'");
             }
         }
 
diff --git a/F-Droid/src/org/fdroid/fdroid/data/Repo.java b/F-Droid/src/org/fdroid/fdroid/data/Repo.java
index fb4cbdd06..28979ec6c 100644
--- a/F-Droid/src/org/fdroid/fdroid/data/Repo.java
+++ b/F-Droid/src/org/fdroid/fdroid/data/Repo.java
@@ -19,13 +19,21 @@ public class Repo extends ValueObject {
     public String address;
     public String name;
     public String description;
-    public int version; // index version, i.e. what fdroidserver built it - 0 if not specified
+    /** index version, i.e. what fdroidserver built it - 0 if not specified */
+    public int version;
     public boolean inuse;
     public int priority;
-    public String pubkey; // null for an unsigned repo
-    public String fingerprint; // always null for an unsigned repo
-    public int maxage; // maximum age of index that will be accepted - 0 for any
-    public String lastetag; // last etag we updated from, null forces update
+    /** The signing certificate, {@code null} for a newly added repo */
+    public String pubkey;
+    /**
+     * The SHA1 fingerprint of {@link #pubkey}, set to {@code null} when a
+     * newly added repo did not include fingerprint. It should never be an
+     * empty {@link String}, i.e. {@code ""} */
+    public String fingerprint;
+    /** maximum age of index that will be accepted - 0 for any */
+    public int maxage;
+    /** last etag we updated from, null forces update */
+    public String lastetag;
     public Date lastUpdated;
     public boolean isSwap;
 
diff --git a/F-Droid/src/org/fdroid/fdroid/localrepo/LocalRepoManager.java b/F-Droid/src/org/fdroid/fdroid/localrepo/LocalRepoManager.java
index ad23254c8..58b64ef9a 100644
--- a/F-Droid/src/org/fdroid/fdroid/localrepo/LocalRepoManager.java
+++ b/F-Droid/src/org/fdroid/fdroid/localrepo/LocalRepoManager.java
@@ -345,11 +345,13 @@ public class LocalRepoManager {
             serializer = XmlPullParserFactory.newInstance().newSerializer();
         }
 
-        public void build(Writer output) throws IOException, LocalRepoKeyStore.InitException {
+        public void build(File file) throws IOException, LocalRepoKeyStore.InitException {
+            Writer output = new FileWriter(file);
             serializer.setOutput(output);
             serializer.startDocument(null, null);
             tagFdroid();
             serializer.endDocument();
+            output.close();
         }
 
         private void tagFdroid() throws IOException, LocalRepoKeyStore.InitException {
@@ -485,16 +487,12 @@ public class LocalRepoManager {
 
     public void writeIndexJar() throws IOException {
 
-        FileWriter writer = null;
         try {
-            writer = new FileWriter(xmlIndex);
-            new IndexXmlBuilder(context, apps).build(writer);
+            new IndexXmlBuilder(context, apps).build(xmlIndex);
         } catch (Exception e) {
             Log.e(TAG, "Could not write index jar", e);
             Toast.makeText(context, R.string.failed_to_create_index, Toast.LENGTH_LONG).show();
             return;
-        } finally {
-            Utils.closeQuietly(writer);
         }
 
         BufferedOutputStream bo = new BufferedOutputStream(new FileOutputStream(xmlIndexJarUnsigned));
diff --git a/F-Droid/src/org/fdroid/fdroid/localrepo/SwapService.java b/F-Droid/src/org/fdroid/fdroid/localrepo/SwapService.java
index 1e5f9b708..09e9e9998 100644
--- a/F-Droid/src/org/fdroid/fdroid/localrepo/SwapService.java
+++ b/F-Droid/src/org/fdroid/fdroid/localrepo/SwapService.java
@@ -259,7 +259,9 @@ public class SwapService extends Service {
             values.put(RepoProvider.DataColumns.NAME, peer.getName());
             values.put(RepoProvider.DataColumns.ADDRESS, peer.getRepoAddress());
             values.put(RepoProvider.DataColumns.DESCRIPTION, "");
-            values.put(RepoProvider.DataColumns.FINGERPRINT, peer.getFingerprint());
+            String fingerprint = peer.getFingerprint();
+            if (!TextUtils.isEmpty(fingerprint))
+                values.put(RepoProvider.DataColumns.FINGERPRINT, peer.getFingerprint());
             values.put(RepoProvider.DataColumns.IN_USE, true);
             values.put(RepoProvider.DataColumns.IS_SWAP, true);
             Uri uri = RepoProvider.Helper.insert(this, values);
diff --git a/F-Droid/src/org/fdroid/fdroid/localrepo/peers/BluetoothPeer.java b/F-Droid/src/org/fdroid/fdroid/localrepo/peers/BluetoothPeer.java
index 45261d6d5..4f29b31ec 100644
--- a/F-Droid/src/org/fdroid/fdroid/localrepo/peers/BluetoothPeer.java
+++ b/F-Droid/src/org/fdroid/fdroid/localrepo/peers/BluetoothPeer.java
@@ -7,6 +7,7 @@ import org.fdroid.fdroid.R;
 import org.fdroid.fdroid.localrepo.type.BluetoothSwap;
 
 public class BluetoothPeer implements Peer {
+    private static final String TAG = "BluetoothPeer";
 
     private BluetoothDevice device;
 
@@ -40,13 +41,15 @@ public class BluetoothPeer implements Peer {
     }
 
     /**
-     * Bluetooth will exclusively be TOFU. Once a device is connected to a bluetooth socket,
-     * if we trust it enough to accept a fingerprint from it somehow, then we may as well trust it
-     * enough to receive an index from it that contains a fingerprint we can use.
+     * Return the fingerprint of the signing key, or {@code null} if it is not set.
+     * <p/>
+     * This is not yet stored for Bluetooth connections. Once a device is connected to a bluetooth
+     * socket, if we trust it enough to accept a fingerprint from it somehow, then we may as well
+     * trust it enough to receive an index from it that contains a fingerprint we can use.
      */
     @Override
     public String getFingerprint() {
-        return "";
+        return null;
     }
 
     @Override
diff --git a/F-Droid/src/org/fdroid/fdroid/localrepo/peers/BonjourPeer.java b/F-Droid/src/org/fdroid/fdroid/localrepo/peers/BonjourPeer.java
index def234be7..0da35cc0e 100644
--- a/F-Droid/src/org/fdroid/fdroid/localrepo/peers/BonjourPeer.java
+++ b/F-Droid/src/org/fdroid/fdroid/localrepo/peers/BonjourPeer.java
@@ -41,6 +41,9 @@ public class BonjourPeer extends WifiPeer {
         return serviceInfo.getRepoAddress();
     }
 
+    /**
+     * Return the fingerprint of the signing key, or {@code null} if it is not set.
+     */
     @Override
     public String getFingerprint() {
         return serviceInfo.getFingerprint();
diff --git a/F-Droid/src/org/fdroid/fdroid/localrepo/type/BluetoothSwap.java b/F-Droid/src/org/fdroid/fdroid/localrepo/type/BluetoothSwap.java
index 57563250a..7894ebeb9 100644
--- a/F-Droid/src/org/fdroid/fdroid/localrepo/type/BluetoothSwap.java
+++ b/F-Droid/src/org/fdroid/fdroid/localrepo/type/BluetoothSwap.java
@@ -14,7 +14,7 @@ import org.fdroid.fdroid.net.bluetooth.BluetoothServer;
 
 public class BluetoothSwap extends SwapType {
 
-    private static final String TAG = "BluetoothBroadcastType";
+    private static final String TAG = "BluetoothSwap";
     public final static String BLUETOOTH_NAME_TAG = "FDroid:";
 
     private static BluetoothSwap mInstance = null;
diff --git a/F-Droid/src/org/fdroid/fdroid/localrepo/type/BonjourBroadcast.java b/F-Droid/src/org/fdroid/fdroid/localrepo/type/BonjourBroadcast.java
index bd29ea26a..3d6743858 100644
--- a/F-Droid/src/org/fdroid/fdroid/localrepo/type/BonjourBroadcast.java
+++ b/F-Droid/src/org/fdroid/fdroid/localrepo/type/BonjourBroadcast.java
@@ -20,7 +20,7 @@ import javax.jmdns.ServiceInfo;
  */
 public class BonjourBroadcast extends SwapType {
 
-    private static final String TAG = "BonjourSwapService";
+    private static final String TAG = "BonjourBroadcast";
 
     private JmDNS jmdns;
     private ServiceInfo pairService;
diff --git a/F-Droid/src/org/fdroid/fdroid/localrepo/type/WifiSwap.java b/F-Droid/src/org/fdroid/fdroid/localrepo/type/WifiSwap.java
index 2d6bd629e..33ef06172 100644
--- a/F-Droid/src/org/fdroid/fdroid/localrepo/type/WifiSwap.java
+++ b/F-Droid/src/org/fdroid/fdroid/localrepo/type/WifiSwap.java
@@ -21,7 +21,7 @@ import java.util.Random;
 
 public class WifiSwap extends SwapType {
 
-    private static final String TAG = "WebServerType";
+    private static final String TAG = "WifiSwap";
 
     private Handler webServerThreadHandler = null;
     private LocalHTTPD localHttpd;
diff --git a/F-Droid/src/org/fdroid/fdroid/net/WifiStateChangeService.java b/F-Droid/src/org/fdroid/fdroid/net/WifiStateChangeService.java
index 860371ec8..5befdbaf2 100644
--- a/F-Droid/src/org/fdroid/fdroid/net/WifiStateChangeService.java
+++ b/F-Droid/src/org/fdroid/fdroid/net/WifiStateChangeService.java
@@ -207,7 +207,8 @@ public class WifiStateChangeService extends Service {
                         // the following methods were not added until android-9/Gingerbread
                         for (InterfaceAddress address : netIf.getInterfaceAddresses()) {
                             if (inetAddress.equals(address.getAddress()) && !TextUtils.isEmpty(FDroidApp.ipAddressString)) {
-                                String cidr = String.format("%s/%d", FDroidApp.ipAddressString, address.getNetworkPrefixLength());
+                                String cidr = String.format(Locale.ENGLISH, "%s/%d",
+                                        FDroidApp.ipAddressString, address.getNetworkPrefixLength());
                                 FDroidApp.subnetInfo = (new SubnetUtils(cidr)).getInfo();
                                 break;
                             }
diff --git a/F-Droid/src/org/fdroid/fdroid/views/fragments/AvailableAppsFragment.java b/F-Droid/src/org/fdroid/fdroid/views/fragments/AvailableAppsFragment.java
index 8b907f510..8ce67a395 100644
--- a/F-Droid/src/org/fdroid/fdroid/views/fragments/AvailableAppsFragment.java
+++ b/F-Droid/src/org/fdroid/fdroid/views/fragments/AvailableAppsFragment.java
@@ -84,7 +84,11 @@ public class AvailableAppsFragment extends AppListFragment implements
             // Wanted to just do this update here, but android tells
             // me that "Only the original thread that created a view
             // hierarchy can touch its views."
-            getActivity().runOnUiThread(new Runnable() {
+            final Activity activity = getActivity();
+            // this nullguard is temporary, this Fragment really needs to merged into the Activity
+            if (activity == null)
+                return;
+            activity.runOnUiThread(new Runnable() {
                 @Override
                 public void run() {
                     if (adapter == null) {