Merge pull request #869 from RandomRoot/feature-yandexotp

Feature: Add Yandex OTP support

app/src/main/java/com/beemdevelopment/aegis/crypto/otp/HOTP.java

@@ -14,18 +14,7 @@ public class HOTP {
 
     public static OTP generateOTP(byte[] secret, String algo, int digits, long counter)
             throws NoSuchAlgorithmException, InvalidKeyException {
-        SecretKeySpec key = new SecretKeySpec(secret, "RAW");
-
-        // encode counter in big endian
-        byte[] counterBytes = ByteBuffer.allocate(8)
-                .order(ByteOrder.BIG_ENDIAN)
-                .putLong(counter)
-                .array();
-
-        // calculate the hash of the counter
-        Mac mac = Mac.getInstance(algo);
-        mac.init(key);
-        byte[] hash = mac.doFinal(counterBytes);
+        byte[] hash = getHash(secret, algo, counter);
 
         // truncate hash to get the HTOP value
         // http://tools.ietf.org/html/rfc4226#section-5.4
@@ -37,4 +26,20 @@ public class HOTP {
 
         return new OTP(otp, digits);
     }
+
+    public static byte[] getHash(byte[] secret, String algo, long counter)
+            throws NoSuchAlgorithmException, InvalidKeyException {
+        SecretKeySpec key = new SecretKeySpec(secret, "RAW");
+
+        // encode counter in big endian
+        byte[] counterBytes = ByteBuffer.allocate(8)
+                .order(ByteOrder.BIG_ENDIAN)
+                .putLong(counter)
+                .array();
+
+        // calculate the hash of the counter
+        Mac mac = Mac.getInstance(algo);
+        mac.init(key);
+        return mac.doFinal(counterBytes);
+    }
 }

app/src/main/java/com/beemdevelopment/aegis/crypto/otp/YAOTP.java

@@ -0,0 +1,83 @@
+package com.beemdevelopment.aegis.crypto.otp;
+
+import androidx.annotation.NonNull;
+
+import com.beemdevelopment.aegis.util.YandexUtils;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.security.InvalidKeyException;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.Arrays;
+
+public class YAOTP {
+    private static final int EN_ALPHABET_LENGTH = 26;
+    private final long _code;
+    private final int _digits;
+
+    private YAOTP(long code, int digits) {
+        _code = code;
+        _digits = digits;
+    }
+
+    public static YAOTP generateOTP(byte[] secret, byte[] pin, int digits, String otpAlgo, long period)
+            throws NoSuchAlgorithmException, InvalidKeyException, IOException {
+        long seconds = System.currentTimeMillis() / 1000;
+        return generateOTP(secret, pin, digits, otpAlgo, seconds, period);
+    }
+
+    public static YAOTP generateOTP(byte[] secret, byte[] pin, int digits, String otpAlgo, long seconds, long period)
+            throws NoSuchAlgorithmException, InvalidKeyException, IOException {
+
+        long counter = (long) Math.floor((double) seconds / period);
+
+        try (ByteArrayOutputStream pinWithHashStream =
+                     new ByteArrayOutputStream(pin.length + secret.length)) {
+
+            pinWithHashStream.write(pin);
+            pinWithHashStream.write(secret, 0, YandexUtils.APPROVED_SECRET_LENGTH);
+
+            MessageDigest md = MessageDigest.getInstance("SHA-256");
+            byte[] keyHash = md.digest(pinWithHashStream.toByteArray());
+
+            if (keyHash[0] == 0) {
+                keyHash = Arrays.copyOfRange(keyHash, 1, keyHash.length);
+            }
+
+            byte[] periodHash = HOTP.getHash(keyHash, otpAlgo, counter);
+            int offset = periodHash[periodHash.length - 1] & 0xf;
+
+            periodHash[offset] &= 0x7f;
+            long otp = ByteBuffer.wrap(periodHash)
+                    .order(ByteOrder.BIG_ENDIAN)
+                    .getLong(offset);
+
+            return new YAOTP(otp, digits);
+        }
+    }
+
+    public long getCode() {
+        return _code;
+    }
+
+    public int getDigits() {
+        return _digits;
+    }
+
+    @NonNull
+    @Override
+    public String toString() {
+        long code = _code % (long) Math.pow(EN_ALPHABET_LENGTH, _digits);
+        char[] chars = new char[_digits];
+
+        for (int i = _digits - 1; i >= 0; i--) {
+            chars[i] = (char) ('a' + (code % EN_ALPHABET_LENGTH));
+            code /= EN_ALPHABET_LENGTH;
+        }
+
+        return new String(chars);
+    }
+}

app/src/main/java/com/beemdevelopment/aegis/otp/GoogleAuthInfo.java

@@ -26,42 +26,6 @@ public class GoogleAuthInfo implements Serializable {
         _issuer = issuer;
     }
 
-    public OtpInfo getOtpInfo() {
-        return _info;
-    }
-
-    public Uri getUri() {
-        Uri.Builder builder = new Uri.Builder();
-        builder.scheme(SCHEME);
-
-        if (_info instanceof TotpInfo) {
-            if (_info instanceof SteamInfo) {
-                builder.authority("steam");
-            } else {
-                builder.authority("totp");
-            }
-            builder.appendQueryParameter("period", Integer.toString(((TotpInfo)_info).getPeriod()));
-        } else if (_info instanceof HotpInfo) {
-            builder.authority("hotp");
-            builder.appendQueryParameter("counter", Long.toString(((HotpInfo)_info).getCounter()));
-        } else {
-            throw new RuntimeException(String.format("Unsupported OtpInfo type: %s", _info.getClass()));
-        }
-
-        builder.appendQueryParameter("digits", Integer.toString(_info.getDigits()));
-        builder.appendQueryParameter("algorithm", _info.getAlgorithm(false));
-        builder.appendQueryParameter("secret", Base32.encode(_info.getSecret()));
-
-        if (_issuer != null && !_issuer.equals("")) {
-            builder.path(String.format("%s:%s", _issuer, _accountName));
-            builder.appendQueryParameter("issuer", _issuer);
-        } else {
-            builder.path(_accountName);
-        }
-
-        return builder.build();
-    }
-
     public static GoogleAuthInfo parseUri(String s) throws GoogleAuthInfoException {
         Uri uri = Uri.parse(s);
         if (uri == null) {
@@ -84,12 +48,13 @@ public class GoogleAuthInfo implements Serializable {
 
         byte[] secret;
         try {
-            secret = parseSecret(encodedSecret);
+            secret = uri.getHost().equals(YandexInfo.OTP_SCHEMA_ID) ? parseYandexSecret(encodedSecret) : parseSecret(encodedSecret);
         } catch (EncodingException e) {
             throw new GoogleAuthInfoException(uri, "Bad secret", e);
         }
 
         OtpInfo info;
+        String issuer = "";
         try {
             String type = uri.getHost();
             if (type == null) {
@@ -122,10 +87,15 @@ public class GoogleAuthInfo implements Serializable {
                     hotpInfo.setCounter(Long.parseLong(counter));
                     info = hotpInfo;
                     break;
+                case YandexInfo.OTP_SCHEMA_ID:
+                    String pinValue = uri.getQueryParameter("pin");
+                    info = pinValue != null ? new YandexInfo(secret, parseSecret(pinValue)) : new YandexInfo(secret);
+                    issuer = info.getType();
+                    break;
                 default:
                     throw new GoogleAuthInfoException(uri, String.format("Unsupported OTP type: %s", type));
             }
-        } catch (OtpInfoException | NumberFormatException e) {
+        } catch (OtpInfoException | NumberFormatException | EncodingException e) {
             throw new GoogleAuthInfoException(uri, e);
         }
 
@@ -134,7 +104,6 @@ public class GoogleAuthInfo implements Serializable {
         String label = path != null && path.length() > 0 ? path.substring(1) : "";
 
         String accountName = "";
-        String issuer = "";
 
         if (label.contains(":")) {
             // a label can only contain one colon
@@ -151,7 +120,9 @@ public class GoogleAuthInfo implements Serializable {
             // label only contains the account name
             // grab the issuer's info from the 'issuer' parameter if it's present
             String issuerParam = uri.getQueryParameter("issuer");
-            issuer = issuerParam != null ? issuerParam : "";
+            if (issuer.isEmpty()) {
+                issuer = issuerParam != null ? issuerParam : "";
+            }
             accountName = label;
         }
 
@@ -180,6 +151,19 @@ public class GoogleAuthInfo implements Serializable {
         return Base32.decode(s);
     }
 
+    /**
+     * When arrives from Yandex site QR code - there will always be 26 symbols (secret only)
+     * If it arrives from Aegis Export - it can be 42 (if was manually created)
+     * Just to be sure, let's check secret length (until final RFC comes up)
+     */
+    public static byte[] parseYandexSecret(String s) throws EncodingException {
+        if (s.length() == YandexInfo.SECRET_LENGTH || s.length() == YandexInfo.SECRET_FULL_LENGTH) {
+            return parseSecret(s);
+        } else {
+            throw new EncodingException(new Throwable("Length differs from expected"));
+        }
+    }
+
     public static Export parseExportUri(String s) throws GoogleAuthInfoException {
         Uri uri = Uri.parse(s);
         if (uri == null) {
@@ -260,7 +244,7 @@ public class GoogleAuthInfo implements Serializable {
                     default:
                         throw new GoogleAuthInfoException(uri, String.format("Unsupported algorithm: %d", params.getType().ordinal()));
                 }
-            } catch (OtpInfoException e){
+            } catch (OtpInfoException e) {
                 throw new GoogleAuthInfoException(uri, e);
             }
 
@@ -279,6 +263,48 @@ public class GoogleAuthInfo implements Serializable {
         return new Export(infos, payload.getBatchId(), payload.getBatchIndex(), payload.getBatchSize());
     }
 
+    public OtpInfo getOtpInfo() {
+        return _info;
+    }
+
+    public Uri getUri() {
+        Uri.Builder builder = new Uri.Builder();
+        builder.scheme(SCHEME);
+
+        if (_info instanceof TotpInfo) {
+            if (_info instanceof SteamInfo) {
+                builder.authority("steam");
+            } else if (_info instanceof YandexInfo) {
+                builder.authority(YandexInfo.OTP_SCHEMA_ID);
+            } else {
+                builder.authority("totp");
+            }
+            builder.appendQueryParameter("period", Integer.toString(((TotpInfo) _info).getPeriod()));
+        } else if (_info instanceof HotpInfo) {
+            builder.authority("hotp");
+            builder.appendQueryParameter("counter", Long.toString(((HotpInfo) _info).getCounter()));
+        } else {
+            throw new RuntimeException(String.format("Unsupported OtpInfo type: %s", _info.getClass()));
+        }
+
+        builder.appendQueryParameter("digits", Integer.toString(_info.getDigits()));
+        builder.appendQueryParameter("algorithm", _info.getAlgorithm(false));
+        builder.appendQueryParameter("secret", Base32.encode(_info.getSecret()));
+
+        if (_info instanceof YandexInfo) {
+            builder.appendQueryParameter("pin", Base32.encode(((YandexInfo) _info).getPinBytes()));
+        }
+
+        if (_issuer != null && !_issuer.equals("")) {
+            builder.path(String.format("%s:%s", _issuer, _accountName));
+            builder.appendQueryParameter("issuer", _issuer);
+        } else {
+            builder.path(_accountName);
+        }
+
+        return builder.build();
+    }
+
     public String getIssuer() {
         return _issuer;
     }

app/src/main/java/com/beemdevelopment/aegis/otp/OtpInfo.java

@@ -115,6 +115,10 @@ public abstract class OtpInfo implements Serializable {
                 case HotpInfo.ID:
                     info = new HotpInfo(secret, algo, digits, obj.getLong("counter"));
                     break;
+                case YandexInfo.ID:
+                    byte[] pin = Base32.decode(obj.getString("pin"));
+                    info = new YandexInfo(secret, pin);
+                    break;
                 default:
                     throw new OtpInfoException("unsupported otp type: " + type);
             }

app/src/main/java/com/beemdevelopment/aegis/otp/YandexInfo.java

@@ -0,0 +1,89 @@
+package com.beemdevelopment.aegis.otp;
+
+import com.beemdevelopment.aegis.crypto.otp.YAOTP;
+import com.beemdevelopment.aegis.encoding.Base32;
+
+import org.json.JSONException;
+import org.json.JSONObject;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+import java.util.Arrays;
+import java.util.Locale;
+
+public class YandexInfo extends TotpInfo {
+    public static final String DEFAULT_ALGORITHM = "SHA256";
+    public static final int DIGITS = 8;
+
+    public static final int SECRET_LENGTH = 26;
+    public static final int SECRET_FULL_LENGTH = 42;
+    public static final String ID = "yandex";
+    public static final String OTP_SCHEMA_ID = "yaotp";
+
+    private byte[] _pin;
+
+    public YandexInfo(byte[] secret) throws OtpInfoException {
+        super(secret, DEFAULT_ALGORITHM, DIGITS, TotpInfo.DEFAULT_PERIOD);
+    }
+
+    public YandexInfo(byte[] secret, byte[] pin) throws OtpInfoException {
+        super(secret, DEFAULT_ALGORITHM, DIGITS, TotpInfo.DEFAULT_PERIOD);
+        this._pin = pin;
+    }
+
+    @Override
+    public String getOtp() {
+        try {
+            YAOTP otp = YAOTP.generateOTP(getSecret(), _pin, getDigits(), getAlgorithm(true), getPeriod());
+            return otp.toString();
+        } catch (InvalidKeyException | NoSuchAlgorithmException | IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    public String getPin() {
+        return _pin != null ? new String(_pin, StandardCharsets.UTF_8) : "";
+    }
+
+    public byte[] getPinBytes() {
+        return _pin;
+    }
+
+    @Override
+    public String getTypeId() {
+        return ID;
+    }
+
+    @Override
+    public String getType() {
+        String id = getTypeId();
+        return id.substring(0, 1).toUpperCase(Locale.ROOT) + id.substring(1);
+    }
+
+    @Override
+    public JSONObject toJson() {
+        JSONObject result = super.toJson();
+        try {
+            result.put("pin", Base32.encode(getPinBytes()));
+        } catch (JSONException e) {
+            throw new RuntimeException(e);
+        }
+        return result;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (!(o instanceof YandexInfo)) return false;
+
+        YandexInfo that = (YandexInfo) o;
+        return super.equals(o) && Arrays.equals(_pin, that._pin);
+    }
+
+    @Override
+    public int hashCode() {
+        return super.hashCode() + Arrays.hashCode(_pin);
+    }
+}

app/src/main/java/com/beemdevelopment/aegis/ui/EditEntryActivity.java

@@ -32,6 +32,7 @@ import androidx.documentfile.provider.DocumentFile;
 import com.amulyakhare.textdrawable.TextDrawable;
 import com.avito.android.krop.KropView;
 import com.beemdevelopment.aegis.R;
+import com.beemdevelopment.aegis.crypto.CryptoUtils;
 import com.beemdevelopment.aegis.encoding.Base32;
 import com.beemdevelopment.aegis.encoding.EncodingException;
 import com.beemdevelopment.aegis.helpers.DropdownHelper;
@@ -46,6 +47,7 @@ import com.beemdevelopment.aegis.otp.OtpInfo;
 import com.beemdevelopment.aegis.otp.OtpInfoException;
 import com.beemdevelopment.aegis.otp.SteamInfo;
 import com.beemdevelopment.aegis.otp.TotpInfo;
+import com.beemdevelopment.aegis.otp.YandexInfo;
 import com.beemdevelopment.aegis.ui.dialogs.Dialogs;
 import com.beemdevelopment.aegis.ui.dialogs.IconPickerDialog;
 import com.beemdevelopment.aegis.ui.glide.IconLoader;
@@ -53,6 +55,7 @@ import com.beemdevelopment.aegis.ui.tasks.ImportFileTask;
 import com.beemdevelopment.aegis.ui.views.IconAdapter;
 import com.beemdevelopment.aegis.util.Cloner;
 import com.beemdevelopment.aegis.util.IOUtils;
+import com.beemdevelopment.aegis.util.YandexUtils;
 import com.beemdevelopment.aegis.vault.VaultEntry;
 import com.beemdevelopment.aegis.vault.VaultManager;
 import com.bumptech.glide.Glide;
@@ -101,6 +104,8 @@ public class EditEntryActivity extends AegisActivity {
     private TextInputEditText _textDigits;
     private TextInputLayout _textDigitsLayout;
     private TextInputEditText _textSecret;
+    private TextInputEditText _textYandexPin;
+    private LinearLayout _textYandexPinLayout;
     private TextInputEditText _textUsageCount;
     private TextInputEditText _textNote;
 
@@ -153,6 +158,8 @@ public class EditEntryActivity extends AegisActivity {
         _textDigits = findViewById(R.id.text_digits);
         _textDigitsLayout = findViewById(R.id.text_digits_layout);
         _textSecret = findViewById(R.id.text_secret);
+        _textYandexPin = findViewById(R.id.text_yandex_pin);
+        _textYandexPinLayout = findViewById(R.id.layout_yandex_pin);
         _textUsageCount = findViewById(R.id.text_usage_count);
         _textNote = findViewById(R.id.text_note);
         _dropdownType = findViewById(R.id.dropdown_type);
@@ -166,12 +173,20 @@ public class EditEntryActivity extends AegisActivity {
 
         // if this is NOT a manually entered entry, move the "Secret" field from basic to advanced settings
         if (!_isNew || (_isNew && !_isManual)) {
+            int secretIndex = 0;
             LinearLayout layoutSecret = findViewById(R.id.layout_secret);
             LinearLayout layoutBasic = findViewById(R.id.layout_basic);
             LinearLayout layoutAdvanced = findViewById(R.id.layout_advanced);
             layoutBasic.removeView(layoutSecret);
-            layoutAdvanced.addView(layoutSecret, 0);
-            ((LinearLayout.LayoutParams) layoutSecret.getLayoutParams()).topMargin = 0;
+            if (!_isNew) {
+                secretIndex = 1;
+                layoutBasic.removeView(_textYandexPinLayout);
+                layoutAdvanced.addView(_textYandexPinLayout, 0);
+                ((LinearLayout.LayoutParams) _textYandexPinLayout.getLayoutParams()).topMargin = 0;
+            } else {
+                ((LinearLayout.LayoutParams) layoutSecret.getLayoutParams()).topMargin = 0;
+            }
+            layoutAdvanced.addView(layoutSecret, secretIndex);
 
             if (_isNew && !_isManual) {
                 setViewEnabled(layoutAdvanced, false);
@@ -206,6 +221,7 @@ public class EditEntryActivity extends AegisActivity {
         _textNote.setText(_origEntry.getNote());
 
         OtpInfo info = _origEntry.getInfo();
+
         if (info instanceof TotpInfo) {
             _textPeriodCounterLayout.setHint(R.string.period_hint);
             _textPeriodCounter.setText(Integer.toString(((TotpInfo) info).getPeriod()));
@@ -225,7 +241,13 @@ public class EditEntryActivity extends AegisActivity {
 
         _dropdownType.setText(_origEntry.getInfo().getType(), false);
         _dropdownAlgo.setText(_origEntry.getInfo().getAlgorithm(false), false);
+
+        if (info instanceof YandexInfo) {
+            _textYandexPin.setText(((YandexInfo) info).getPin());
+        }
+
         updateAdvancedFieldStatus(_origEntry.getInfo().getTypeId());
+        updatePinFieldVisibility(_origEntry.getInfo().getTypeId());
 
         String group = _origEntry.getGroup();
         setGroup(group);
@@ -254,11 +276,18 @@ public class EditEntryActivity extends AegisActivity {
                     _textPeriodCounter.setText(String.valueOf(HotpInfo.DEFAULT_COUNTER));
                     _textDigits.setText(String.valueOf(OtpInfo.DEFAULT_DIGITS));
                     break;
+                case YandexInfo.ID:
+                    _dropdownAlgo.setText(YandexInfo.DEFAULT_ALGORITHM, false);
+                    _textPeriodCounterLayout.setHint(R.string.period_hint);
+                    _textPeriodCounter.setText(String.valueOf(TotpInfo.DEFAULT_PERIOD));
+                    _textDigits.setText(String.valueOf(YandexInfo.DIGITS));
+                    break;
                 default:
                     throw new RuntimeException(String.format("Unsupported OTP type: %s", type));
             }
 
             updateAdvancedFieldStatus(type);
+            updatePinFieldVisibility(type);
         });
 
         _iconView.setOnClickListener(v -> {
@@ -290,12 +319,17 @@ public class EditEntryActivity extends AegisActivity {
     }
 
     private void updateAdvancedFieldStatus(String otpType) {
-        boolean enabled = !otpType.equals(SteamInfo.ID) && (!_isNew || _isManual);
+        boolean enabled = !otpType.equals(SteamInfo.ID) && !otpType.equals(YandexInfo.ID) && (!_isNew || _isManual);
         _textDigitsLayout.setEnabled(enabled);
         _textPeriodCounterLayout.setEnabled(enabled);
         _dropdownAlgoLayout.setEnabled(enabled);
     }
 
+    private void updatePinFieldVisibility(String otpType) {
+        boolean visible = otpType.equals(YandexInfo.ID);
+        _textYandexPinLayout.setVisibility(visible ? View.VISIBLE : View.GONE);
+    }
+
     private void setGroup(String groupName) {
         int pos = 0;
         if (groupName != null) {
@@ -627,6 +661,14 @@ public class EditEntryActivity extends AegisActivity {
 
         String type = _dropdownType.getText().toString();
         String algo = _dropdownAlgo.getText().toString();
+        String lowerCasedType = type.toLowerCase(Locale.ROOT);
+
+        if (lowerCasedType.equals(YandexInfo.ID)) {
+            int pinLength = _textYandexPin.length();
+            if (pinLength < 4) {
+                throw new ParseException("PIN is a required field. Min 4 digits.");
+            }
+        }
 
         int digits;
         try {
@@ -664,6 +706,12 @@ public class EditEntryActivity extends AegisActivity {
                     }
                     info = new HotpInfo(secret, algo, digits, counter);
                     break;
+                case YandexInfo.OTP_SCHEMA_ID:
+                case YandexInfo.ID:
+                    YandexUtils.validateSecret(secret);
+                    byte[] pin = CryptoUtils.toBytes(_textYandexPin.getText().toString().toCharArray());
+                    info = new YandexInfo(secret, pin);
+                    break;
                 default:
                     throw new RuntimeException(String.format("Unsupported OTP type: %s", type));
             }

app/src/main/java/com/beemdevelopment/aegis/ui/views/EntryHolder.java

@@ -22,6 +22,7 @@ import com.beemdevelopment.aegis.otp.HotpInfo;
 import com.beemdevelopment.aegis.otp.OtpInfo;
 import com.beemdevelopment.aegis.otp.SteamInfo;
 import com.beemdevelopment.aegis.otp.TotpInfo;
+import com.beemdevelopment.aegis.otp.YandexInfo;
 import com.beemdevelopment.aegis.ui.glide.IconLoader;
 import com.beemdevelopment.aegis.vault.VaultEntry;
 import com.bumptech.glide.Glide;
@@ -238,7 +239,7 @@ public class EntryHolder extends RecyclerView.ViewHolder {
         OtpInfo info = _entry.getInfo();
 
         String otp = info.getOtp();
-        if (!(info instanceof SteamInfo)) {
+        if (!(info instanceof SteamInfo || info instanceof YandexInfo)) {
             otp = formatCode(otp);
         }
 

app/src/main/java/com/beemdevelopment/aegis/util/YandexUtils.java

@@ -0,0 +1,89 @@
+package com.beemdevelopment.aegis.util;
+
+import com.beemdevelopment.aegis.otp.OtpInfoException;
+import com.beemdevelopment.aegis.otp.YandexInfo;
+
+public class YandexUtils {
+    private static final char CHECKSUM_POLY = 0b1_1000_1111_0011;
+    public static final int APPROVED_SECRET_LENGTH = 16;
+
+    private YandexUtils() {
+    }
+
+    private static int getNumberOfLeadingZeros(char value) {
+        if (value == 0) return 16;
+
+        int n = 0;
+        if ((value & 0xFF00) == 0) {
+            n += 8;
+            value <<= 8;
+        }
+        if ((value & 0xF000) == 0) {
+            n += 4;
+            value <<= 4;
+        }
+        if ((value & 0xC000) == 0) {
+            n += 2;
+            value <<= 2;
+        }
+        if ((value & 0x8000) == 0) {
+            n++;
+        }
+
+        return n;
+    }
+
+    /**
+     * Java implementation of ChecksumIsValid
+     * from https://github.com/norblik/KeeYaOtp/blob/dev/KeeYaOtp/Core/Secret.cs
+     */
+    public static void validateSecret(byte[] secret) throws OtpInfoException {
+        /*
+            When secret comes from QR code - we can't test it,
+            cause it's only 16 byte long.
+         */
+        if (secret.length == APPROVED_SECRET_LENGTH) return;
+
+        if (secret.length != YandexInfo.SECRET_LENGTH)
+            throw new OtpInfoException("Wrong secret size");
+
+        char originalChecksum = (char) ((secret[secret.length - 2] & 0x0F) << 8 | secret[secret.length - 1] & 0xff);
+
+        char accum = 0;
+        int accumBits = 0;
+
+        int inputTotalBitsAvailable = secret.length * 8 - 12;
+        int inputIndex = 0;
+        int inputBitsAvailable = 8;
+
+        while (inputTotalBitsAvailable > 0) {
+            int requiredBits = 13 - accumBits;
+            if (inputTotalBitsAvailable < requiredBits) requiredBits = inputTotalBitsAvailable;
+
+            while (requiredBits > 0) {
+                int curInput = (secret[inputIndex] & (1 << inputBitsAvailable) - 1) & 0xff;
+                int bitsToRead = Math.min(requiredBits, inputBitsAvailable);
+
+                curInput >>= inputBitsAvailable - bitsToRead;
+                accum = (char) (accum << bitsToRead | curInput);
+
+                inputTotalBitsAvailable -= bitsToRead;
+                requiredBits -= bitsToRead;
+                inputBitsAvailable -= bitsToRead;
+                accumBits += bitsToRead;
+
+                if (inputBitsAvailable == 0) {
+                    inputIndex += 1;
+                    inputBitsAvailable = 8;
+                }
+            }
+
+            if (accumBits == 13) accum ^= CHECKSUM_POLY;
+            accumBits = 16 - getNumberOfLeadingZeros(accum);
+        }
+
+        if (accum != originalChecksum) {
+            throw new OtpInfoException("Secret is corrupted. Checksum is not valid");
+        }
+    }
+}