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Tuesday, November 27, 2018

Skype Hype/Gripe

Hello again readers and welcome back! Based off the title of this blog post, I am pretty sure that you already know that we will be covering Skype in this post. As with any good story, it is best to start at the beginning of this magical journey....

Chapter 1: Data generation

As some of you may know, I have been involved with the Cyber Sleuth Science Lab since this summer, working on bringing STEM (specifically digital forensics) to high school aged students. This project requires a tremendous amount of behind the scenes work, especially in the scenario data generation realm. For the next phase of the project, we decided that utilizing Skype would be the best chat application to use, because not only could we generate data across several platforms, but we can also extract it in a reliable method from mobile devices. So, I created some Skype conversations on my test device (a Samsung Galaxy S6 Edge, specifically SM-G925F (remember the model number, you will see it again)), made a full image of it, and loaded it into Magnet AXIOM, which the folks at Magnet Forensics have generously made available to the Cyber Sleuth participants. And, surprisingly, I was met with this:
Processing in AXIOM found the "main.db" file, but nothing else

Obviously I knew something wasn't right, as I definitely populated data in the application, which I could easily see. But it was not detected in AXIOM, so I had to dig into this a bit more.

Chapter 2: A sorta "new" discovery. Kinda-ish

Obviously one of the main aspects in our career field is that we trust tools to extract known data from known places, but at any time that can change and we have to update our methods (and tools) accordingly. I told Jessica about a possible new discovery when I found this at the beginning of November, which I had to put aside for a few weeks as I took part in an incident response case. This week I was able to jump back into it again, and worked on trying to figure out exactly "what" was happening here. Initially, the thought was that Skype had changed a whole bunch of stuff. As it turns out (thankfully) that is not quite the case, but it does bring up a couple of issues to keep in mind if you are looking at mobile devices with Skype usage.

The first item to note is the presence of the file "main.db". Historically this was located under the "databases" folder, but now it is located under the "files" folder, specifically under the subfolder "live#<username>". 

The main.db file, historically, was not in this location

Contents of "main.db". Notice the lack of data in the tables

There is a "databases" folder though, so naturally the next step was to look there. Sure enough, this contained what looks like the database(s) we are looking for

The "new" contents of the "databases" folder
Naturally I was drawn to the "live:iamsarahthompson1990.db" database, as the other two databases have fairly mundane names, plus the file size was considerably larger. 

Chapter 3: Parsing the data

Now that I had identified my database, it was a question of figuring out what table was going to contain what I was looking for. Fortunately most of the tables follow an easy to recognize naming conventions, so I focused my efforts on the "chatItem" table

The table "chatItem" from the user database

I need to do some more testing on what the flags actually mean, but for now this particular SQLite query should work quite well if you also come across it (please keep reading though, as there are caveats on WHEN to use this query)

SELECT DATETIME(chatItem.time / 1000, 'unixepoch') as "Date/Time (UTC)", person_id as Sender, content as Message, CASE type WHEN 9 THEN "Received" WHEN 10 THEN "Sent" WHEN 12 THEN "Multimedia Sent" WHEN 1 THEN "Unknown" END as "Type", status as "Status", CASE deleted WHEN 1 THEN "Yes" WHEN 0 Then "" END as "Deleted", edited as "Edited", retry as "Retry", file_name as "Multimedia File Name", device_gallery_path as "Multimedia Path On Device" FROM chatItem

Once you input the above SQLite query, you can end up with a nicely formatted output which is easy to look at, like this (the output was pasted from SQLite Spy to a tsv file, then opened and formatted in Excel)

Cleaned up Skype chats

Chapter 4: What the heck is going on here??

After much discussion on exactly "what" was happening here with Jessica, it turns out that it is actually a couple of things that all combined to have the data stored like this.

First of all, remember the model number that I listed? Well, this is the Global version of the Galaxy S6 Edge. That means that some apps are pre-bundled, and in this case Microsoft apps (including Skype) were included by default. After I updated the app to what looked like the latest version on the Play Store, I did my data pull (I chose to do this, rather than pull from APK Mirror, because I wanted to see if the latest app version was supported with my tools). However, one important caveat to note, is that this device is running Android 5.1.1 (because it is super easy to root an older version of Android and get a full image of the device, which is what is needed for the data analysis portion of the Cyber Sleuth workshop). Android 5 currently accounts for almost 18% of all Android devices on the market (kinda surprising, I know). 

Android market saturation as of October 26, 2018, retrieved on November 27, 2018 from

The issue here is that although according to the Google Play Store I was updating to the latest version of Skype, in reality because the "new" versions of Skype are not compatible with older Android versions (by default the SM-G925F (told you that you would see it again) ships with Android 5), it was actually installing "Skype Lite". Even though, as you can clearly see from the screenshots, the Google Play Store was telling me that "Skype" was indeed installed, and "Skype Lite" was not. 

"Skype" application information from the S6 Edge

According to this, Skype is installed

This screen suggests that "Skype Lite" is a different application

This confirms that, according to the Play Store, "Skype Lite" is indeed a different application on my Galaxy S6 Edge running Android 5.1.1

Chapter 5: Whew. No changes. But support is needed

As you may have guessed, Skype Lite actually stores data in a different fashion than traditional Skype itself. Most of the tools on the market today are set to handle Skype data, but not Skype Lite. This is the reason that AXIOM did not detect Skype data, because it does not (yet) have the support for Skype Lite, it only has support for Skype itself. And although it was initially suspected, Skype itself did not undergo a drastic change, it was just a combination of things that resulted in Android/Google Play/Skype doing something that was totally unexpected, because of the the base installation of Android that was running.

NOTE: If I was running Android 6 or later on the device, the aforementioned tools should parse the data, but we will have to hold onto that thought for testing for another day :)

Chapter 6: The Grand Finale

If you made it all the way down here, congratulations for sticking with this adventure. It has definitely been a fun one! 

Always remember that, at the end of the day, tools are just tools, and they have limitations and shortcomings. In a perfect world every tool could handle all the data from every application from every device. But we all know that is not going to happen. Don't be afraid to dig into the data itself, because you might find that an entire data structure is not being parsed properly. Or that the formats have changed. Or, you may find through a series of events that your device is running a different application, with a different storage structure, than what the device is "telling" you what is really running!