Prevent the creation of 'weak' PINs.

Simple checks to prevent the same number, or sequentially
increasing/decreasing PINs. e.g. 1111, 1234, 54321, etc.

app/src/main/java/org/thoughtcrime/securesms/lock/v2/CreateKbsPinFragment.java

@@ -1,15 +1,20 @@
 package org.thoughtcrime.securesms.lock.v2;
 
-import android.view.View;
+import android.view.animation.Animation;
+import android.view.animation.TranslateAnimation;
+import android.widget.EditText;
+import android.widget.Toast;
 
 import androidx.annotation.NonNull;
 import androidx.annotation.PluralsRes;
 import androidx.autofill.HintConstants;
+import androidx.core.content.ContextCompat;
 import androidx.core.view.ViewCompat;
 import androidx.lifecycle.ViewModelProviders;
 import androidx.navigation.Navigation;
 
 import org.thoughtcrime.securesms.R;
+import org.thoughtcrime.securesms.util.SpanUtil;
 
 public class CreateKbsPinFragment extends BaseKbsPinFragment<CreateKbsPinViewModel> {
 
@@ -47,6 +52,15 @@ public class CreateKbsPinFragment extends BaseKbsPinFragment<CreateKbsPinViewMod
     CreateKbsPinFragmentArgs args      = CreateKbsPinFragmentArgs.fromBundle(requireArguments());
 
     viewModel.getNavigationEvents().observe(getViewLifecycleOwner(), e -> onConfirmPin(e.getUserEntry(), e.getKeyboard(), args.getIsPinChange()));
+    viewModel.getErrorEvents().observe(getViewLifecycleOwner(), e -> {
+      if (e == CreateKbsPinViewModel.PinErrorEvent.WEAK_PIN) {
+        getLabel().setText(SpanUtil.color(ContextCompat.getColor(requireContext(), R.color.red),
+                                          getString(R.string.CreateKbsPinFragment__choose_a_stronger_pin)));
+        shake(getInput(), () -> getInput().getText().clear());
+      } else {
+        throw new AssertionError("Unexpected PIN error!");
+      }
+    });
     viewModel.getKeyboard().observe(getViewLifecycleOwner(), k -> {
       getLabel().setText(getLabelText(k));
       getInput().getText().clear();
@@ -76,4 +90,23 @@ public class CreateKbsPinFragment extends BaseKbsPinFragment<CreateKbsPinViewMod
   private String getPinLengthRestrictionText(@PluralsRes int plurals) {
     return requireContext().getResources().getQuantityString(plurals, KbsConstants.MINIMUM_PIN_LENGTH, KbsConstants.MINIMUM_PIN_LENGTH);
   }
+
+  private static void shake(@NonNull EditText view, @NonNull Runnable afterwards) {
+    TranslateAnimation shake = new TranslateAnimation(0, 30, 0, 0);
+    shake.setDuration(50);
+    shake.setRepeatCount(7);
+    shake.setAnimationListener(new Animation.AnimationListener() {
+      @Override
+      public void onAnimationStart(Animation animation) {}
+
+      @Override
+      public void onAnimationEnd(Animation animation) {
+        afterwards.run();
+      }
+
+      @Override
+      public void onAnimationRepeat(Animation animation) {}
+    });
+    view.startAnimation(shake);
+  }
 }

app/src/main/java/org/thoughtcrime/securesms/lock/v2/CreateKbsPinViewModel.java

@@ -2,18 +2,22 @@ package org.thoughtcrime.securesms.lock.v2;
 
 import androidx.annotation.MainThread;
 import androidx.annotation.NonNull;
+import androidx.annotation.StringRes;
 import androidx.core.util.Preconditions;
 import androidx.lifecycle.LiveData;
 import androidx.lifecycle.MutableLiveData;
 import androidx.lifecycle.ViewModel;
 
+import org.thoughtcrime.securesms.R;
 import org.thoughtcrime.securesms.util.SingleLiveEvent;
+import org.whispersystems.signalservice.internal.registrationpin.PinValidityChecker;
 
 public final class CreateKbsPinViewModel extends ViewModel implements BaseKbsPinViewModel {
 
   private final MutableLiveData<KbsPin>          userEntry = new MutableLiveData<>(KbsPin.EMPTY);
   private final MutableLiveData<PinKeyboardType> keyboard  = new MutableLiveData<>(PinKeyboardType.NUMERIC);
   private final SingleLiveEvent<NavigationEvent> events    = new SingleLiveEvent<>();
+  private final SingleLiveEvent<PinErrorEvent>   errors    = new SingleLiveEvent<>();
 
   @Override
   public LiveData<KbsPin> getUserEntry() {
@@ -27,6 +31,8 @@ public final class CreateKbsPinViewModel extends ViewModel implements BaseKbsPin
 
   LiveData<NavigationEvent> getNavigationEvents() { return events; }
 
+  LiveData<PinErrorEvent> getErrorEvents() { return errors; }
+
   @Override
   @MainThread
   public void setUserEntry(String userEntry) {
@@ -42,8 +48,14 @@ public final class CreateKbsPinViewModel extends ViewModel implements BaseKbsPin
   @Override
   @MainThread
   public void confirm() {
-    events.setValue(new NavigationEvent(Preconditions.checkNotNull(this.getUserEntry().getValue()),
-                                        Preconditions.checkNotNull(this.getKeyboard().getValue())));
+    KbsPin          pin      = Preconditions.checkNotNull(this.getUserEntry().getValue());
+    PinKeyboardType keyboard = Preconditions.checkNotNull(this.getKeyboard().getValue());
+
+    if (PinValidityChecker.valid(pin.toString())) {
+      events.setValue(new NavigationEvent(pin, keyboard));
+    } else {
+      errors.setValue(PinErrorEvent.WEAK_PIN);
+    }
   }
 
   static final class NavigationEvent {
@@ -63,4 +75,8 @@ public final class CreateKbsPinViewModel extends ViewModel implements BaseKbsPin
       return keyboard;
     }
   }
+
+  enum PinErrorEvent {
+    WEAK_PIN
+  }
 }

app/src/main/res/values/strings.xml

@@ -1930,6 +1930,7 @@
     <string name="CreateKbsPinFragment__you_can_choose_a_new_pin_as_long_as_this_device_is_registered">You can change your PIN as long as this device is registered.</string>
     <string name="CreateKbsPinFragment__create_your_pin">Create your PIN</string>
     <string name="CreateKbsPinFragment__pins_keep_information_stored_with_signal_encrypted">PINs keep information stored with Signal encrypted so only you can access it. Your profile, settings, and contacts will restore when you reinstall Signal.</string>
+    <string name="CreateKbsPinFragment__choose_a_stronger_pin">Choose a stronger PIN</string>
 
     <!-- ConfirmKbsPinFragment -->
     <string name="ConfirmKbsPinFragment__pins_dont_match">PINs don\'t match. Try again.</string>

app/src/test/java/org/thoughtcrime/securesms/registration/v2/PinValidityChecker_validity_Test.java

@@ -0,0 +1,38 @@
+package org.thoughtcrime.securesms.registration.v2;
+
+import org.junit.Test;
+import org.thoughtcrime.securesms.registration.v2.testdata.PinValidityVector;
+import org.thoughtcrime.securesms.util.Util;
+import org.whispersystems.signalservice.internal.registrationpin.PinValidityChecker;
+import org.whispersystems.signalservice.internal.util.JsonUtil;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+public final class PinValidityChecker_validity_Test {
+
+  @Test
+  public void vectors_valid() throws IOException {
+    for (PinValidityVector vector : getKbsPinValidityTestVectorList()) {
+      boolean valid = PinValidityChecker.valid(vector.getPin());
+
+      assertEquals(String.format("%s [%s]", vector.getName(), vector.getPin()),
+                   vector.isValid(),
+                   valid);
+    }
+  }
+
+  private static PinValidityVector[] getKbsPinValidityTestVectorList() throws IOException {
+    try (InputStream resourceAsStream = ClassLoader.getSystemClassLoader().getResourceAsStream("data/kbs_pin_validity_vectors.json")) {
+
+      PinValidityVector[] data = JsonUtil.fromJson(Util.readFullyAsString(resourceAsStream), PinValidityVector[].class);
+
+      assertTrue(data.length > 0);
+
+      return data;
+    }
+  }
+}

app/src/test/java/org/thoughtcrime/securesms/registration/v2/testdata/PinValidityVector.java

@@ -0,0 +1,27 @@
+package org.thoughtcrime.securesms.registration.v2.testdata;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+public class PinValidityVector {
+
+  @JsonProperty("name")
+  private String name;
+
+  @JsonProperty("pin")
+  private String pin;
+
+  @JsonProperty("valid")
+  private boolean valid;
+
+  public String getName() {
+    return name;
+  }
+
+  public String getPin() {
+    return pin;
+  }
+
+  public boolean isValid() {
+    return valid;
+  }
+}

app/src/test/resources/data/kbs_pin_validity_vectors.json

@@ -0,0 +1,62 @@
+[
+  {
+    "name": "Empty",
+    "pin": "",
+    "valid": false
+  },
+  {
+    "name": "Alpha",
+    "pin": "abcd",
+    "valid": true
+  },
+  {
+    "name": "Sequential",
+    "pin": "1234",
+    "valid": false
+  },
+  {
+    "name": "Non-sequential",
+    "pin": "6485",
+    "valid": true
+  },
+  {
+    "name": "Sequential descending",
+    "pin": "43210",
+    "valid": false
+  },
+  {
+    "name": "Sequential with space",
+    "pin": "1234 ",
+    "valid": false
+  },
+  {
+    "name": "Non-sequential with space",
+    "pin": "1236 ",
+    "valid": true
+  },
+  {
+    "name": "Sequential Non-arabic digits",
+    "pin": "١٢٣٤٥",
+    "valid": false
+  },
+  {
+    "name": "Sequential descending Non-arabic digits",
+    "pin": "٥٤٣٢١",
+    "valid": false
+  },
+  {
+    "name": "Non-sequential Non-arabic digits",
+    "pin": "١٢٣٥٤",
+    "valid": true
+  },
+  {
+    "name": "All digits the same",
+    "pin": "9999",
+    "valid": false
+  },
+  {
+    "name": "All Non-arabic digits the same",
+    "pin": "٢٢٢٢",
+    "valid": false
+  }
+]

libsignal/service/src/main/java/org/whispersystems/signalservice/internal/registrationpin/PinHasher.java

@@ -10,8 +10,8 @@ public final class PinHasher {
   public static byte[] normalize(String pin) {
     pin = pin.trim();
 
-    if (allNumeric(pin)) {
-      pin = new String(toArabic(pin));
+    if (PinString.allNumeric(pin)) {
+      pin = PinString.toArabic(pin);
     }
 
     pin = Normalizer.normalize(pin, Normalizer.Form.NFKD);
@@ -26,27 +26,4 @@ public final class PinHasher {
   public interface Argon2 {
     byte[] hash(byte[] password);
   }
-
-  private static boolean allNumeric(CharSequence pin) {
-    for (int i = 0; i < pin.length(); i++) {
-      if (!Character.isDigit(pin.charAt(i))) return false;
-    }
-    return true;
-  }
-
-  /**
-   * Converts a string of not necessarily Arabic numerals to Arabic 0..9 characters.
-   */
-  private static char[] toArabic(CharSequence numerals) {
-    int length = numerals.length();
-    char[] arabic = new char[length];
-
-    for (int i = 0; i < length; i++) {
-      int digit = Character.digit(numerals.charAt(i), 10);
-
-      arabic[i] = (char) ('0' + digit);
-    }
-
-    return arabic;
-  }
 }

libsignal/service/src/main/java/org/whispersystems/signalservice/internal/registrationpin/PinString.java

@@ -0,0 +1,32 @@
+package org.whispersystems.signalservice.internal.registrationpin;
+
+import org.whispersystems.signalservice.api.kbs.HashedPin;
+
+import java.nio.charset.StandardCharsets;
+import java.text.Normalizer;
+
+final class PinString {
+
+  static boolean allNumeric(CharSequence pin) {
+    for (int i = 0; i < pin.length(); i++) {
+      if (!Character.isDigit(pin.charAt(i))) return false;
+    }
+    return true;
+  }
+
+  /**
+   * Converts a string of not necessarily Arabic numerals to Arabic 0..9 characters.
+   */
+  static String toArabic(CharSequence numerals) {
+    int length = numerals.length();
+    char[] arabic = new char[length];
+
+    for (int i = 0; i < length; i++) {
+      int digit = Character.digit(numerals.charAt(i), 10);
+
+      arabic[i] = (char) ('0' + digit);
+    }
+
+    return new String(arabic);
+  }
+}

libsignal/service/src/main/java/org/whispersystems/signalservice/internal/registrationpin/PinValidityChecker.java

@@ -0,0 +1,73 @@
+package org.whispersystems.signalservice.internal.registrationpin;
+
+public final class PinValidityChecker {
+
+  public static boolean valid(String pin) {
+    pin = pin.trim();
+
+    if (pin.isEmpty()) {
+      return false;
+    }
+
+    if (PinString.allNumeric(pin)) {
+      pin = PinString.toArabic(pin);
+
+      return !sequential(pin) &&
+             !sequential(reverse(pin)) &&
+             !allTheSame(pin);
+    } else {
+      return true;
+    }
+  }
+
+  private static String reverse(String string) {
+    char[] chars = string.toCharArray();
+
+    for (int i = 0; i < chars.length / 2; i++) {
+      char temp = chars[i];
+      chars[i] = chars[chars.length - i - 1];
+      chars[chars.length - i - 1] = temp;
+    }
+
+    return new String(chars);
+  }
+
+  private static boolean sequential(String pin) {
+    int length = pin.length();
+
+    if (length == 0) {
+      return false;
+    }
+
+    char c = pin.charAt(0);
+
+    for (int i = 1; i < length; i++) {
+      char n = pin.charAt(i);
+      if (n != c + 1) {
+        return false;
+      }
+      c = n;
+    }
+
+    return true;
+  }
+
+  private static boolean allTheSame(String pin) {
+    int length = pin.length();
+
+    if (length == 0) {
+      return false;
+    }
+
+    char c = pin.charAt(0);
+
+    for (int i = 1; i < length; i++) {
+      char n = pin.charAt(i);
+      if (n != c) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+}