don't allow to purge keys. offer distrut instead

src/main/java/eu/siacs/conversations/crypto/axolotl/AxolotlService.java

@@ -439,8 +439,10 @@ public class AxolotlService implements OnAdvancedStreamFeaturesLoaded {
 		mXmppConnectionService.sendIqPacket(account, publish, null);
 	}
 
-	public void purgeKey(final String fingerprint) {
-		axolotlStore.setFingerprintStatus(fingerprint.replaceAll("\\s", ""), FingerprintStatus.createCompromised());
+	public void distrustFingerprint(final String fingerprint) {
+		final String fp = fingerprint.replaceAll("\\s", "");
+		final FingerprintStatus fingerprintStatus = axolotlStore.getFingerprintStatus(fp);
+		axolotlStore.setFingerprintStatus(fp,fingerprintStatus.toUntrusted());
 	}
 
 	public void publishOwnDeviceIdIfNeeded() {

src/main/java/eu/siacs/conversations/crypto/axolotl/FingerprintStatus.java

@@ -126,13 +126,6 @@ public class FingerprintStatus implements Comparable<FingerprintStatus> {
         return trust;
     }
 
-    public static FingerprintStatus createCompromised() {
-        FingerprintStatus status = new FingerprintStatus();
-        status.active = false;
-        status.trust = Trust.COMPROMISED;
-        return status;
-    }
-
     public FingerprintStatus toVerified() {
         FingerprintStatus status = new FingerprintStatus();
         status.active = active;
@@ -140,6 +133,13 @@ public class FingerprintStatus implements Comparable<FingerprintStatus> {
         return status;
     }
 
+    public FingerprintStatus toUntrusted() {
+        FingerprintStatus status = new FingerprintStatus();
+        status.active = active;
+        status.trust = Trust.UNTRUSTED;
+        return status;
+    }
+
     public static FingerprintStatus createInactiveVerified() {
         final FingerprintStatus status = new FingerprintStatus();
         status.trust = Trust.VERIFIED;

src/main/java/eu/siacs/conversations/crypto/axolotl/XmppAxolotlSession.java

@@ -118,6 +118,8 @@ public class XmppAxolotlSession implements Comparable<XmppAxolotlSession> {
 					setTrust(status.toActive());
 				}
 			}
+		} else {
+			Log.d(Config.LOGTAG,account.getJid().toBareJid()+" not encrypting omemo message from fingerprint "+getFingerprint()+" because it was marked as compromised");
 		}
 		return plaintext;
 	}

src/main/java/eu/siacs/conversations/ui/OmemoActivity.java

@@ -24,8 +24,6 @@ import eu.siacs.conversations.R;
 import eu.siacs.conversations.crypto.axolotl.FingerprintStatus;
 import eu.siacs.conversations.crypto.axolotl.XmppAxolotlSession;
 import eu.siacs.conversations.entities.Account;
-import eu.siacs.conversations.ui.TrustKeysActivity;
-import eu.siacs.conversations.ui.XmppActivity;
 import eu.siacs.conversations.ui.widget.Switch;
 import eu.siacs.conversations.utils.CryptoHelper;
 import eu.siacs.conversations.utils.XmppUri;
@@ -51,16 +49,17 @@ public abstract class OmemoActivity extends XmppActivity {
                 && fingerprint instanceof String
                 && fingerprintStatus instanceof FingerprintStatus) {
             getMenuInflater().inflate(R.menu.omemo_key_context, menu);
-            MenuItem purgeItem = menu.findItem(R.id.purge_omemo_key);
+            MenuItem distrust = menu.findItem(R.id.distrust_key);
             MenuItem verifyScan = menu.findItem(R.id.verify_scan);
             if (this instanceof TrustKeysActivity) {
-                purgeItem.setVisible(false);
+                distrust.setVisible(false);
                 verifyScan.setVisible(false);
             } else {
                 FingerprintStatus status = (FingerprintStatus) fingerprintStatus;
                 if (!status.isActive() || status.isVerified()) {
                     verifyScan.setVisible(false);
                 }
+                distrust.setVisible(status.isVerified());
             }
             this.mSelectedAccount = (Account) account;
             this.mSelectedFingerprint = (String) fingerprint;
@@ -70,7 +69,7 @@ public abstract class OmemoActivity extends XmppActivity {
     @Override
     public boolean onContextItemSelected(MenuItem item) {
         switch (item.getItemId()) {
-            case R.id.purge_omemo_key:
+            case R.id.distrust_key:
                 showPurgeKeyDialog(mSelectedAccount,mSelectedFingerprint);
                 break;
             case R.id.copy_omemo_key:
@@ -242,17 +241,14 @@ public abstract class OmemoActivity extends XmppActivity {
 
     public void showPurgeKeyDialog(final Account account, final String fingerprint) {
         AlertDialog.Builder builder = new AlertDialog.Builder(this);
-        builder.setTitle(getString(R.string.purge_key));
-        builder.setIconAttribute(android.R.attr.alertDialogIcon);
-        builder.setMessage(getString(R.string.purge_key_desc_part1)
-                + "\n\n" + CryptoHelper.prettifyFingerprint(fingerprint.substring(2))
-                + "\n\n" + getString(R.string.purge_key_desc_part2));
+        builder.setTitle(R.string.distrust_omemo_key);
+        builder.setMessage(R.string.distrust_omemo_key_text);
         builder.setNegativeButton(getString(R.string.cancel), null);
-        builder.setPositiveButton(getString(R.string.purge_key),
+        builder.setPositiveButton(R.string.confirm,
                 new DialogInterface.OnClickListener() {
                     @Override
                     public void onClick(DialogInterface dialog, int which) {
-                        account.getAxolotlService().purgeKey(fingerprint);
+                        account.getAxolotlService().distrustFingerprint(fingerprint);
                         refreshUi();
                     }
                 });

src/main/res/menu/omemo_key_context.xml

@@ -5,8 +5,8 @@
         android:title="@string/scan_qr_code"
         />
     <item
-        android:id="@+id/purge_omemo_key"
-        android:title="@string/purge_key"/>
+        android:id="@+id/distrust_key"
+        android:title="@string/distrust_omemo_key"/>
     <item
         android:id="@+id/copy_omemo_key"
         android:title="@string/copy_fingerprint"/>

src/main/res/values/strings.xml

@@ -429,9 +429,6 @@
 	<string name="wipe_omemo_pep">Wipe other devices from PEP</string>
 	<string name="clear_other_devices">Clear devices</string>
 	<string name="clear_other_devices_desc">Are you sure you want to clear all other devices from the OMEMO announcement? The next time your devices connect, they will reannounce themselves, but they might not receive messages sent in the meantime.</string>
-	<string name="purge_key">Purge key</string>
-	<string name="purge_key_desc_part1">Are you sure you want to purge this key?</string>
-	<string name="purge_key_desc_part2">It will irreversibly be considered compromised, and you can never build a session with it again.</string>
 	<string name="error_no_keys_to_trust_server_error">There are no usable keys available for this contact.\nFetching new keys from the server has been unsuccessful. Maybe there is something wrong with your contacts server.</string>
 	<string name="error_no_keys_to_trust">There are no usable keys available for this contact. If you have purged any of their keys, they need to generate new ones.</string>
 	<string name="error_trustkeys_title">Error</string>
@@ -725,4 +722,6 @@
 	<string name="verify_omemo_keys">Verify OMEMO keys</string>
 	<string name="show_inactive_devices">Show inactive devices</string>
 	<string name="hide_inactive_devices">Hide inactive devices</string>
+	<string name="distrust_omemo_key">Distrust device</string>
+	<string name="distrust_omemo_key_text">Are you sure you want to remove the verification for this device?\nThis device and messages coming from that device will be marked as untrusted.</string>
 </resources>