Add Numeric9x4PassphraseUtils

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/util/Numeric9x4PassphraseUtil.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2017 Schürmann & Breitmoser GbR
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.sufficientlysecure.keychain.util;
+
+
+import java.nio.CharBuffer;
+import java.security.SecureRandom;
+import java.util.Random;
+import java.util.regex.Pattern;
+
+import android.support.annotation.VisibleForTesting;
+
+// see https://autocrypt.org/level1.html#setup-code
+public class Numeric9x4PassphraseUtil {
+    public static Passphrase generateNumeric9x4Passphrase() {
+        return generateNumeric9x4Passphrase(new SecureRandom());
+    }
+
+    @VisibleForTesting
+    static Passphrase generateNumeric9x4Passphrase(Random r) {
+        StringBuilder code = new StringBuilder(36);
+        for (int i = 0; i < 36; i++) {
+            boolean isBeginningOfBlock = i > 0 && (i % 4) == 0;
+            if (isBeginningOfBlock) {
+                code.append('-');
+            }
+
+            String digit = Integer.toString(r.nextInt(10));
+            code.append(digit);
+        }
+
+        return new Passphrase(code.toString());
+    }
+
+    private static final Pattern AUTOCRYPT_TRANSFER_CODE = Pattern.compile("(\\d{4}-){8}\\d{4}");
+
+    public static boolean isNumeric9x4Passphrase(Passphrase transferCodeChars) {
+        return isNumeric9x4Passphrase(CharBuffer.wrap(transferCodeChars.getCharArray()));
+    }
+
+    public static boolean isNumeric9x4Passphrase(CharSequence code) {
+        return AUTOCRYPT_TRANSFER_CODE.matcher(code).matches();
+    }
+}