Support for full backup/restore to sdcard

src/org/thoughtcrime/securesms/backup/FullBackupBase.java

@@ -0,0 +1,62 @@
+package org.thoughtcrime.securesms.backup;
+
+
+import android.support.annotation.NonNull;
+import android.util.Log;
+
+import org.greenrobot.eventbus.EventBus;
+import org.whispersystems.libsignal.util.ByteUtil;
+
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+
+public abstract class FullBackupBase {
+
+  private static final String TAG = FullBackupBase.class.getSimpleName();
+
+  protected static @NonNull byte[] getBackupKey(@NonNull String passphrase) {
+    try {
+      EventBus.getDefault().post(new BackupEvent(BackupEvent.Type.PROGRESS, 0));
+
+      MessageDigest digest = MessageDigest.getInstance("SHA-512");
+      byte[]        input  = passphrase.replace(" ", "").getBytes();
+      byte[]        hash   = input;
+
+      long start = System.currentTimeMillis();
+      for (int i=0;i<250000;i++) {
+        if (i % 1000 == 0) EventBus.getDefault().post(new BackupEvent(BackupEvent.Type.PROGRESS, 0));
+        digest.update(hash);
+        hash = digest.digest(input);
+      }
+      Log.w(TAG, "Generated: " + (System.currentTimeMillis()- start));
+
+      return ByteUtil.trim(hash, 32);
+    } catch (NoSuchAlgorithmException e) {
+      throw new AssertionError(e);
+    }
+  }
+
+  public static class BackupEvent {
+    public enum Type {
+      PROGRESS,
+      FINISHED
+    }
+
+    private final Type type;
+    private final int count;
+
+    BackupEvent(Type type, int count) {
+      this.type  = type;
+      this.count = count;
+    }
+
+    public Type getType() {
+      return type;
+    }
+
+    public int getCount() {
+      return count;
+    }
+  }
+
+}