From 1b5afc32471c5c056acdb1ccdc749eda45f135cf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dominik=20Sch=C3=BCrmann?= <dominik@dominikschuermann.de>
Date: Thu, 27 Aug 2015 21:53:33 +0200
Subject: Experimental word comparison

---
 .../keychain/ui/util/ExperimentalWordConfirm.java  | 126 +++++++++++++++++++++
 1 file changed, 126 insertions(+)
 create mode 100644 OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/util/ExperimentalWordConfirm.java

(limited to 'OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/util')

diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/util/ExperimentalWordConfirm.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/util/ExperimentalWordConfirm.java
new file mode 100644
index 000000000..43ccac24f
--- /dev/null
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/util/ExperimentalWordConfirm.java
@@ -0,0 +1,126 @@
+/*
+ * Copyright (C) 2015 Dominik Schürmann <dominik@dominikschuermann.de>
+ *
+ * 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.ui.util;
+
+import android.content.Context;
+
+import org.spongycastle.util.Arrays;
+import org.sufficientlysecure.keychain.Constants;
+import org.sufficientlysecure.keychain.util.Log;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.ArrayList;
+import java.util.BitSet;
+
+public class ExperimentalWordConfirm {
+
+    public static String getWords(Context context, byte[] fingerprintBlob) {
+        ArrayList<String> words = new ArrayList<>();
+
+        BufferedReader reader = null;
+        try {
+            reader = new BufferedReader(new InputStreamReader(
+                    context.getAssets().open("word_confirm_list.txt"),
+                    "UTF-8"
+            ));
+
+            String line = reader.readLine();
+            while (line != null) {
+                words.add(line);
+
+                line = reader.readLine();
+            }
+        } catch (IOException e) {
+            throw new RuntimeException("IOException", e);
+        } finally {
+            if (reader != null) {
+                try {
+                    reader.close();
+                } catch (IOException ignored) {
+                }
+            }
+        }
+
+        String fingerprint = "";
+
+        // NOTE: 160 bit SHA-1 truncated to 156 bit
+        byte[] fingerprintBlobTruncated = Arrays.copyOfRange(fingerprintBlob, 0, 156 / 8);
+
+        // TODO: implement key stretching to minimize fp length?
+
+        // BitSet bits = BitSet.valueOf(fingerprintBlob);  // min API 19 and little endian!
+        BitSet bits = bitSetToByteArray(fingerprintBlobTruncated);
+        Log.d(Constants.TAG, "bits: " + bits.toString());
+
+        final int CHUNK_SIZE = 13;
+        final int LAST_CHUNK_INDEX = fingerprintBlobTruncated.length * 8 / CHUNK_SIZE; // 12
+        Log.d(Constants.TAG, "LAST_CHUNK_INDEX: " + LAST_CHUNK_INDEX);
+
+        int from = 0;
+        int to = CHUNK_SIZE;
+        for (int i = 0; i < (LAST_CHUNK_INDEX + 1); i++) {
+            Log.d(Constants.TAG, "from: " + from + " to: " + to);
+
+            BitSet setIndex = bits.get(from, to);
+            int wordIndex = (int) bitSetToLong(setIndex);
+            // int wordIndex = (int) setIndex.toLongArray()[0]; // min API 19
+
+            fingerprint += words.get(wordIndex);
+
+            if (i != LAST_CHUNK_INDEX) {
+                // line break every 3 words
+                if (to % (CHUNK_SIZE * 3) == 0) {
+                    fingerprint += "\n";
+                } else {
+                    fingerprint += " ";
+                }
+            }
+
+            from = to;
+            to += CHUNK_SIZE;
+        }
+
+        return fingerprint;
+    }
+
+    /**
+     * Returns a BitSet containing the values in bytes.
+     * BIG ENDIAN!
+     */
+    private static BitSet bitSetToByteArray(byte[] bytes) {
+        int arrayLength = bytes.length * 8;
+        BitSet bits = new BitSet();
+
+        for (int i = 0; i < arrayLength; i++) {
+            if ((bytes[bytes.length - i / 8 - 1] & (1 << (i % 8))) > 0) {
+                bits.set(i);
+            }
+        }
+        return bits;
+    }
+
+    private static long bitSetToLong(BitSet bits) {
+        long value = 0L;
+        for (int i = 0; i < bits.length(); ++i) {
+            value += bits.get(i) ? (1L << i) : 0L;
+        }
+        return value;
+    }
+}
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