From d09ad45e112bf5ce5e50ab4bb0ed651dccdc8775 Mon Sep 17 00:00:00 2001
From: Albert Vaca Cintora <albertvaka@gmail.com>
Date: Thu, 26 Nov 2020 11:30:46 +0100
Subject: [PATCH] Add a verification key that's displayed when pairing

The key is a sha256 of both devices' certificates. Both should generate the
same key, so hey user can check they are pairing against the right device.

Thanks Matthias Gerstner <mgerstner@suse.de> for reporting this.
---
 res/drawable/ic_key.xml                       | 10 +++++++
 res/layout/activity_device.xml                | 12 ++++++++
 res/values/strings.xml                        |  3 +-
 src/org/kde/kdeconnect/Device.java            |  5 ++--
 .../Helpers/SecurityHelpers/SslHelper.java    | 30 ++++++++++++++++++-
 .../UserInterface/DeviceFragment.java         |  7 +++++
 6 files changed, 63 insertions(+), 4 deletions(-)
 create mode 100644 res/drawable/ic_key.xml

diff --git a/res/drawable/ic_key.xml b/res/drawable/ic_key.xml
new file mode 100644
index 00000000..2316df20
--- /dev/null
+++ b/res/drawable/ic_key.xml
@@ -0,0 +1,10 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24"
+    android:tint="?attr/colorControlNormal">
+  <path
+      android:fillColor="@android:color/white"
+      android:pathData="M12.65,10C11.83,7.67 9.61,6 7,6c-3.31,0 -6,2.69 -6,6s2.69,6 6,6c2.61,0 4.83,-1.67 5.65,-4H17v4h4v-4h2v-4H12.65zM7,14c-1.1,0 -2,-0.9 -2,-2s0.9,-2 2,-2 2,0.9 2,2 -0.9,2 -2,2z"/>
+</vector>
diff --git a/res/layout/activity_device.xml b/res/layout/activity_device.xml
index 2e6debab..f9d6cf6a 100644
--- a/res/layout/activity_device.xml
+++ b/res/layout/activity_device.xml
@@ -30,6 +30,18 @@
             android:text="@string/device_not_paired"
             android:textAppearance="?android:attr/textAppearanceMedium"/>
 
+        <TextView
+            android:id="@+id/pair_verification"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:drawablePadding="5dp"
+            android:drawableLeft="@drawable/ic_key"
+            android:drawableStart="@drawable/ic_key"
+            android:layout_marginBottom="8dip"
+            android:visibility="gone"
+            android:text=""
+            android:textAppearance="?android:attr/textAppearanceMedium"/>
+
         <Button
             android:id="@+id/pair_button"
             android:layout_width="match_parent"
diff --git a/res/values/strings.xml b/res/values/strings.xml
index 0503030a..446bb62c 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -126,9 +126,10 @@
     <string name="encryption_info_title">Encryption Info</string>
     <string name="encryption_info_msg_no_ssl">The other device doesn\'t use a recent version of KDE Connect, using the legacy encryption method.</string>
     <string name="my_device_fingerprint">SHA1 fingerprint of your device certificate is:</string>
-    <string name="remote_device_fingerprint">SHA1 fingerprint of remote device certificate is:</string>
+    <string name="remote_device_fingerprint">SHA256 fingerprint of remote device certificate is:</string>
     <string name="pair_requested">Pair requested</string>
     <string name="pairing_request_from">Pairing request from %1s</string>
+    <string name="pairing_verification_code" translatable="false">🔑%1s...</string>
     <plurals name="incoming_file_title">Receiving file from %1s>
         <item quantity="one">Receiving %1$d file from %2$s</item>
         <item quantity="other">Receiving %1$d files from %2$s</item>
diff --git a/src/org/kde/kdeconnect/Device.java b/src/org/kde/kdeconnect/Device.java
index 6f75520f..b5a0cb9d 100644
--- a/src/org/kde/kdeconnect/Device.java
+++ b/src/org/kde/kdeconnect/Device.java
@@ -391,10 +391,11 @@ public class Device implements BaseLink.PacketReceiver {
 
         final NotificationManager notificationManager = ContextCompat.getSystemService(getContext(), NotificationManager.class);
 
+        String verificationKeyShort = SslHelper.getVerificationKey(SslHelper.certificate, certificate).substring(8);
+
         Notification noti = new NotificationCompat.Builder(getContext(), NotificationHelper.Channels.DEFAULT)
                 .setContentTitle(res.getString(R.string.pairing_request_from, getName()))
-                .setContentText(res.getString(R.string.tap_to_answer))
-                .setContentIntent(pendingIntent)
+                .setContentText(res.getString(R.string.pairing_verification_code, verificationKeyShort))
                 .setTicker(res.getString(R.string.pair_requested))
                 .setSmallIcon(R.drawable.ic_notification)
                 .addAction(R.drawable.ic_accept_pairing_24dp, res.getString(R.string.pairing_accept), acceptedPendingIntent)
diff --git a/src/org/kde/kdeconnect/Helpers/SecurityHelpers/SslHelper.java b/src/org/kde/kdeconnect/Helpers/SecurityHelpers/SslHelper.java
index b0462e36..a7a3cc35 100644
--- a/src/org/kde/kdeconnect/Helpers/SecurityHelpers/SslHelper.java
+++ b/src/org/kde/kdeconnect/Helpers/SecurityHelpers/SslHelper.java
@@ -30,6 +30,7 @@ import org.spongycastle.cert.jcajce.JcaX509v3CertificateBuilder;
 import org.spongycastle.jce.provider.BouncyCastleProvider;
 import org.spongycastle.operator.ContentSigner;
 import org.spongycastle.operator.jcajce.JcaContentSignerBuilder;
+import org.spongycastle.util.Arrays;
 
 import java.io.IOException;
 import java.math.BigInteger;
@@ -254,7 +255,7 @@ public class SslHelper {
 
     public static String getCertificateHash(Certificate certificate) {
         try {
-            byte[] hash = MessageDigest.getInstance("SHA-1").digest(certificate.getEncoded());
+            byte[] hash = MessageDigest.getInstance("SHA-256").digest(certificate.getEncoded());
             Formatter formatter = new Formatter();
             int i;
             for (i = 0; i < hash.length - 1; i++) {
@@ -279,4 +280,31 @@ public class SslHelper {
         return IETFUtils.valueToString(rdn.getFirst().getValue());
     }
 
+    public static String getVerificationKey(X509Certificate certificateA, Certificate certificateB) {
+        try {
+            byte[] a = certificateA.getPublicKey().getEncoded();
+            byte[] b = certificateB.getPublicKey().getEncoded();
+
+            if (Arrays.compareUnsigned(a, b) < 0) {
+                // Swap them so on both devices they are in the same order
+                byte[] aux = a;
+                a = b;
+                b = aux;
+            }
+
+            byte[] concat = new byte[a.length + b.length];
+            System.arraycopy(a, 0, concat, 0, a.length);
+            System.arraycopy(b, 0, concat, a.length, b.length);
+
+            byte[] hash = MessageDigest.getInstance("SHA-256").digest(concat);
+            Formatter formatter = new Formatter();
+            for (int i = 0; i < hash.length - 1; i++) {
+                formatter.format("%02x", hash[i]);
+            }
+            return formatter.toString();
+        } catch(Exception e) {
+            e.printStackTrace();
+            return "error";
+        }
+    }
 }
diff --git a/src/org/kde/kdeconnect/UserInterface/DeviceFragment.java b/src/org/kde/kdeconnect/UserInterface/DeviceFragment.java
index 5f0f61fb..e28bf1e4 100644
--- a/src/org/kde/kdeconnect/UserInterface/DeviceFragment.java
+++ b/src/org/kde/kdeconnect/UserInterface/DeviceFragment.java
@@ -104,6 +104,8 @@ public class DeviceFragment extends Fragment {
         binding.pairButton.setOnClickListener(v -> {
             binding.pairButton.setVisibility(View.GONE);
             binding.pairMessage.setText("");
+            binding.pairVerification.setVisibility(View.VISIBLE);
+            binding.pairVerification.setText(SslHelper.getVerificationKey(SslHelper.certificate, device.certificate));
             binding.pairProgress.setVisibility(View.VISIBLE);
             BackgroundService.RunCommand(mActivity, service -> {
                 device = service.getDevice(mDeviceId);
@@ -259,6 +261,8 @@ public class DeviceFragment extends Fragment {
             public void run() {
                 if (device.isPairRequestedByPeer()) {
                     binding.pairMessage.setText(R.string.pair_requested);
+                    binding.pairVerification.setVisibility(View.VISIBLE);
+                    binding.pairVerification.setText(SslHelper.getVerificationKey(SslHelper.certificate, device.certificate));
                     binding.pairingButtons.setVisibility(View.VISIBLE);
                     binding.pairProgress.setVisibility(View.GONE);
                     binding.pairButton.setVisibility(View.GONE);
@@ -333,6 +337,8 @@ public class DeviceFragment extends Fragment {
             mActivity.runOnUiThread(() -> {
                 if (binding.getRoot() == null) return;
                 binding.pairMessage.setText(error);
+                binding.pairVerification.setText("");
+                binding.pairVerification.setVisibility(View.GONE);
                 binding.pairProgress.setVisibility(View.GONE);
                 binding.pairButton.setVisibility(View.VISIBLE);
                 binding.pairRequestButtons.setVisibility(View.GONE);
@@ -345,6 +351,7 @@ public class DeviceFragment extends Fragment {
             mActivity.runOnUiThread(() -> {
                 if (binding.getRoot() == null) return;
                 binding.pairMessage.setText(R.string.device_not_paired);
+                binding.pairVerification.setVisibility(View.GONE);
                 binding.pairProgress.setVisibility(View.GONE);
                 binding.pairButton.setVisibility(View.VISIBLE);
                 binding.pairRequestButtons.setVisibility(View.GONE);