remove tiny dependency to spongycastle/bouncycastle

build.gradle

@@ -75,6 +75,7 @@ dependencies {
     compile 'com.google.android.exoplayer:exoplayer:r2.3.1'
 
     compile 'org.whispersystems:signal-service-android:2.7.6'
+    //compile 'com.fasterxml.jackson.core:jackson-databind:2.9.5'
 
     compile 'com.journeyapps:zxing-android-embedded:3.4.0'
 

src/org/thoughtcrime/securesms/attachments/AttachmentServer.java

@@ -6,9 +6,9 @@ import android.net.Uri;
 import android.support.annotation.NonNull;
 import android.util.Log;
 
-import org.spongycastle.util.encoders.Hex;
 import org.thoughtcrime.securesms.mms.PartAuthority;
 import org.thoughtcrime.securesms.util.Util;
+import org.thoughtcrime.securesms.util.Hex;
 
 import java.io.BufferedOutputStream;
 import java.io.BufferedReader;
@@ -52,7 +52,7 @@ public class AttachmentServer implements Runnable {
       this.attachment   = attachment;
       this.socket       = new ServerSocket(0, 0, InetAddress.getByAddress(new byte[]{127, 0, 0, 1}));
       this.port         = socket.getLocalPort();
-      this.auth         = new String(Hex.encode(Util.getSecretBytes(16)));
+      this.auth         = Hex.toStringCondensed(Util.getSecretBytes(16));
 
       this.socket.setSoTimeout(5000);
     } catch (UnknownHostException e) {