Wickr. Alright. We’ll Call It A Draw.

WickrPrompt
Ugh.  Not again.

Portions of this blog post appeared in the 6th issue of the INTERPOL Digital 4n6 Pulse newsletter. 

I would like to thank Heather Mahalik and Or Begam, both of Cellebrite, who helped make the Android database portion of this blog post possible, and Mike Williamson of Magnet Forensics for all the help with the underpinnings of the iOS version.

I have been seeing the above pop-up window lately.  A  lot.  Not to pick on any particular tool vendor, but seeing this window (or one simmilar to it) brings a small bit of misery.  Its existence means there is a high probability there is data on a particular mobile device that I am not going to get access to, and this is usually after I have spent a considerable amount of time trying to gain access to the device itself.  Frustrating.

One of my mentors from my time investigating homicides told me early in my career that I was not doing it right unless I had some unsolved homicides on the books; he felt it was some sort of badge of honor and showed a dedication to the craft.  I think there should be a similar mantra for digital forensic examiners.  If you conduct digital forensic examinations for any substantial amount of time you are going to have examinations where there is inaccesible data and nothing you do is going to change that.  You can throw every tool known to civilization at it, try to manually examine it, phone a friend, look on Twitter, search the blog-o-sphere, search the Discord Channel, query a listserv, and conduct your own research and you still strike out.  This is a reality in our discipline.

Not being able to access such data is no judgment of your abilities, it just means you may not win this round.  Keep in mind there is a larger fight, and how you react to this setback is a reflection of your dedication to our craft.  Do you let inaccessible data defeat you and you give up and quit, or do you carry on with that examination, getting what you can, and apply that same tenacity to future examinations?

One needs the latter mindset when it comes to Wickr.  For those that are unfamilar, Wickr is a company that makes a privacy-focused, ephemeral messaging application. Initially available as an iOS-only app, Wickr expanded their app to include Android, Windows, macOS, and Linux, and branched out from personal messaging (Wickr Me) to small teams and businesses (Wickr Pro – similar to Slack), and an enterprise platform (Wickr Enterprise).  Wickr first hit the app market in 2012, and has been quietly hanging around since then.  Personally, I am surpised it is not as popular as Signal,  but I think not having Edward Snowden’s endorsement and initially being secretive about its protocal may have hurt Wickr’s uptake a bit.

Regardless, this app can bring the pain to examinations.

Before I get started, a few things to note.  First, this post encompasses Android, iOS, macOS, and Windows.  Because of some time constraints I did not have time to test this in Linux.  Second, the devices and respective operating system versions/hardware are as follows:

Platform                    Version                 Device                                                   Wickr Version


Android                      9.0                         Pixel 3                                                    5.22


iOS                               12.4                       iPhone XS and iPad Pro 10.5            5.22


macOS                        10.14.6                  Mac Mini (2018)                                  5.28


Windows 10 Pro       1903                      Surface Pro                                           5.28

Third, Wickr Me contains the same encryption scheme and basic functionality as the Pro and Enterprise versions: encrypted messaging, encrypted file transfer, burn-on-read messages, audio calling, and secure “shredding” of data. The user interface of Wickr Me is similar to the other versions, so the following sections will discuss the functionality of Wickr while using the personal version.

Finally, how do you get the data?  Logical extractions, at a minimum, should grab desktop platform Wickr data during an extraction.  For Android devices, the data resides in the /data/data area of the file system, so if your tool can get to this area, you should be able to get Wickr data.  For iOS devices, you will need a jailbroken phone or an extraction tool such as one that is metal, gray, and can unlock a door to get the Wickr database.  I can confirm that a backup nor a logical extraction contains the iOS Wickr database.

Visual Walkaround

Wickr is available on Android, iOS, macOS, and Windows, and while these platforms are different, the Wickr user interface (UI) is relatively the same across these platforms. Figure 1 shows the Windows UI, Figure 2 shows the macOS UI, Figure 3 shows the iPhone, and Figure 4 shows the iPad. The security posture of the Wickr app on Android prevents screenshots from being taken on the device, so no UI figure is available.  Just know that it looks very similar to Figure 3.

Figure 1
Figure 1.  Wickr in Windows.
Figure 2.png
Figure 2.  Wickr in macOS.

 

Figure 3.png
Figure 3.  Wickr on iPhone.
Figure 4
Figure 4.  Wickr on iPad.

Each figure has certain features highlighted. In each figure the red box shows the icons for setting the expiration timer and burn on read (setting that allows the sender of a message to set a self-destruction timer on a message before it is sent – the recipient has no control over this feature), the blue arrow shows the area where a user composes a message, the orange arrow shows the area where conversations are listed, and the purple arrow shows the contents of the highlighted conversation (chosen in the conversations list).  Not highlighted is the phone icon seen in upper right corner of each figure. This initiates an audio call with the conversation participant(s).

The plus sign seen in the screen (red boxes) reveals a menu that has additional options: send a file (including media files), share a user’s location, or use one of the installed quick responses. Visually, the menu will look slightly different per platform, but the functionality is the same.  See Figure 5.

Figure 5
Figure 5.  Additional activity options (Windows UI).

The sending and receiving of messages and files works as other messaging applications with similar capabilities. Figure 6 shows an active conversation within the macOS UI.

Figure 6.png
Figure 6.  A conversation with a text message and picture attachments (macOS UI).

Wickr is similar to Snapchat in that messages “expire” after a set period of time. The default time a message is active is six (6) days, which is the maximum amount of time a message can be available, but a user can set message retention times as short as one second. This setting is device specific; if a user has multiple devices they can choose different retention periods for each device.

Users can also set “burn-on-read” times in which a message will expire (“burn”) after a certain period of time after the message has been read. This setting is controlled by the message sender, regardless of the recipient’s message retention period setting.  The retention period for burn-on-read messages can also be set anywhere between 1 second and 6 days. Figure 7 shows the Windows Wickr UI when a burn-on-read message has been received and opened (bottom of the active conversation window pane), and Figure 8 shows the same UI after the burn-on-read retention period expired.

Figure 7
Figure 7.  A burn-on-read message (timer in red).
Figure 8
Figure 8.  Poof! The message has been burned.

The Secure Shredder function is Wickr’s feature by which data that has been deleted by the app is rendered unrecoverable by overwriting the deleted data.  Secure Shredder is an automated feature that runs in the background but has a manual configuration feature if a user is part of the Wickr Pro Silver or Gold tiers, which allows users to manually initiate the function.  Testing showed this feature automatically runs every +/- one (1) minute while the device is idle.

Encryption.  All Of The Encryptions.

Wickr is designed with total privacy in mind, so all three versions use the same encryption model. The app not only protects messages, media, and files in transit, but it also protects data at rest. The app has been designed with perfect forward secrecy; if a user’s device is compromised, historical communications are still protected unless the attacker has the user’s password and the messages have not expired.

When a new message is received, it arrives in a “locked” state.  See Figure 9.

Figure 9.png
Figure 9.  A new message.

When a message is sent, the sender’s device will encrypt the message using a symmetric key. To generate the symmetric key, internal APIs gather random numbers which are then run through the AES-256 cryptographic algorithm in Galois/Counter Mode (GCM). Each message is encrypted using a new symmetric key, and this operation occurs strictly on the sender’s device. This encryption happens regardless of whether the message contains text, a file, or a combination of the two. The cipher text and the symmetric key (i.e. the package) are encrypted using the signed public key of the recipient’s device (I’ll discuss asymmetric operations in a minute), and then sent to the recipient who then decrypts the package using their private key. The symmetric key is then applied to the cipher text in order to decrypt it.

The takeaway here is that unlocking a received message = decrypting a received message.  A user may set their device to automatically unlock messages, but the default behavior is to leaved them locked on receipt and manually initiate the unlock.

Asymmetric operations are applied to messages in transit.  As previously mentioned, cipher text and the symmetric key used encrypt it are packaged up and encrypted using the public key of the intended recipient’s device.  The public key is signed with components from said device.  The recipient device uses the corresponding private key to decrypt the package, and then the symmetric key is used to decrypt the cipher text  (unlocking the message) so the recipient can read it. If a message is intended for multiple recipients or for a recipient who has multiple devices, a different set of keys is used for each destination device.

Here is where the pain starts to come. The keys used in the asymmetric operations are ephemeral; a different set of public/private key pairs are used each time a message is exchanged between devices. Wickr states in its technical paper that pools of components (not the actual keys themselves) of private-public pairs are created and refreshed by a user’s device while they are connected to Wickr’s servers.  If a device is disconnected from the Wickr servers, it will use what key pairs it has, and will then refresh its pool once it has re-established the connection.

Even if a private key is compromised, the only message that can be decrypted is the one that corresponds to that specific private/public key pair; the rest of the messages are still safe since they use different pairs.

But wait, it gets worse.  Just to turn the knife a bit more, Wickr has a different encryption scheme for on-device storage that is separate from message transfers.  When Wickr is first installed on a device a Node Storage Root Key (Knsr) is generated. The Knsr is then applied to certain device data (described as “device specific data and/or identifiers derived from installed hardware or operating system resources that are unique, constant across application installs but not necessary secret“) to generate the Local Device Storage Key (Klds). The Klds is used to encrypt Wickr data stored locally on the device, including files necessary for Wickr to operate.

The Klds is itself encrypted using a key derived from the user’s password being passed through scrypt. When a user successfully logs in to the Wickr app, the Klds is decrypted and placed into the device’s memory, allowing for successful exposure of the locally stored Wickr data through the app UI. When the app is terminated, placed in an inactive state, or a user logs out, the Klds is removed from memory, and the Wickr data is no longer available.

For those who have legal processes at their disposal (court orders, search warrants, & subpoenas), the news is equally dire.  Wickr does keep undelivered messages on their servers for up to six (6) days, but, as I previously mentioned, the messages (which are in transit) are encrypted.  Wickr states they do not have acess to any keys that would decrypt what messages are stored.  There is some generic account and device information, but no message content.  For more information on what little they do have, please read their legal process guide.

So, Is There Anything I Can Actually Get?

The answer to this question is the standard digital forensics answer:  “It depends.” The encryption scheme combined with the on-device security measures makes it extremely difficult to recover any useful data from either the app or Wickr, but there is some data that can be retrieved, the value of which depends on the goal of the examination.

Testing has shown a manual examination is the only way, as of the time of this post, to recover message content from iOS, macOS, and Windows (files not included). This requires unfettered access to the device along with the user’s Wickr password. Due to a change in its encryption scheme (when this happened is unknown), Wickr is not supported by any tool I tested on any platform, which included the current versions of Cellebrite, Axiom, and XRY. This included the Android virtualization options offered by two mobile vendors.  Along those same lines, I also tried Alexis Brignoni’s virtualization walkthrough using Nox Player, Virtual Box, and Genymotion, with no luck on all three platforms.

Things can be slightly different for those of you who have Wickr deployed in an enterprise environment.  The enterprise flavor of Wickr does have compliance (think FOIA requests and statutory/regulatory requirements) and eDiscovery features, which means message content may be retained so as long as the feature is enabled (I didn’t have access to this version so I could not ascertain if this was the case).  Just be aware that if the environment includes Wickr, this may be an option for you.

The type and amount of data an examiner can possibly get is dependant upon which platform is being examined. The nice thing is there is some consistency, so this can help examiners determine, rather quickly, if there is anything to be recovered.  The consistencey can be broken up in to two categories:  iOS and Android/macOS/Windows. One thing is consistent across ALL platforms, though: an examiner should not expect to find any message content beyond six (6) days from the time of examination.

Android/macOS/Windows

The most important thing to remember for Android, macOS, and Windows platforms is that order matters when doing a manual examination. That is, the order in which you examine the device for Wickr content is important. Failure to keep this mind may result in recoverable data being deleted unnecessarily.  Android can be slightly different, which I will discuss shortly.

I will go ahead and get one thing out of the way with all three platforms: the databases containing account information, conversation information, contacts, and message content are all encrypted.  The  database is protected with SQL Cipher 3, and the Wickr user password is not the password to the database (I tried to apply the correct Wickr password in DB Browser for SQLite, and none would open – you’ll see why below). Figure 10 shows the macOS database in hexadecimal view and Figure 11 shows the Windows database.  While not shown here, just know the Android database looks the same.

Figure 10.png
Figure 10.  Wickr database in macOS
Figure 11.PNG
Figure 11.  Wickr database in Windows.

You may have noticed the file name for both macOS and Windows is the same:  wickr_db.sqlite.  The similarities do not stop there.  Figure 12 shows the location of the database in macOS, Figure 13 shows the database’s location in Windows.

Figure 12
Figure 12.  Home in macOS.  ~/Users/%UserName%/Library/ApplicationSupport/Wickr, LLC/WickrMe/
Figure 13
Figure 13.  Home in Windows.  C:\Users\%UserName%\AppData\Local\Wickr, LLC\WickrMe\

As you can see, most of the file names in each home directory are the same.  Note that the last folder in the path, “WickrMe,” may be different depending on what version is installed on the device (Wickr Me, Wickr Pro, Enterprise), so just know the last hop in the path may not be exactly the same.

Interesting note about the “preferences” file in Windows:  it is not encrypted.  It can be opened, and doing so reveals quite a bit of octet data.  The field “auid” caught my attention, and while I have a theory about its value, I’ll save it for another blog post.

For Android, the directory and layout should look familar to those who examine Android devices.  The database file, wickr_db, sits in the databases folder.  See Figure 14.

Figure 14
Figure 14.  Home in Android.  /data/data/com.mywickr.wickr2

If you will recall, when a user unlocks a message it is actually decrypting it.  This also applies to files that are sent through Wickr.  Unlike messages, which are stored within the database, files, both encrypted and decrypted, reside in the Wickr portion of the file system.  When a message with a file unlocked, an encrypted version is created within the Wickr portion of the file system.  When the file is opened (not just unlocked), it is decrypted, and a decrypted version of that file is created within a different path within the Wickr portion of the file system.  Figure 15 shows the Android files, Figure 16 shows the macOS files, and Figure 17 shows the Windows files.  The top portion of each figure shows the files in encrypted format and the bottom portion of the figure shows the files in decrypted format.

Figure 15.png
Figure 15.  Encrypted/decrypted files in Android.
Figure 16
Figure 16.  Encrypted/decrypted files in macOS.
Figure 17
Figure 17.  Encrypted/decrypted files in Windows.

When a file is sent through Wickr it is given a GUID, and that GUID is consistent across devices for both the sender and the recipient(s).  In the figures above, Android represents Test Account 1 and macOS/Windows represents Test Account 2, so you will notice that the same GUIDs are seen on both accounts (all three platforms).

The fact an encrypted version of a file exists indicates a device received the file and the message was unlocked, but doesn’t necessarily indicate the file was opened.  It isn’t until the user chooses to open the file within the Wickr UI that a decrypted version is deposited onto the device as seen above.  An example of the open dialogue is seen in Figure 18.  The triple dots in the upper righthand corner of the message bubble invokes the menu.

Figure 18.png
Figure 18.  Open dialogue example (Windows UI).

If a picture is received and the message is unlocked, then a thumbnail is rendered within the Wickr UI message screen, as seen in Figure 18, but this doesn’t deposit a decrypted version of that picture; the user must open the file.  Any other file type, including vidoes, merely display the original file name in the Wickr UI.  A user will have to open the file in order to view its contents.

The directories for files on each platform is as follows (path starts in the Wickr home directory):

Platform                                   Encrypted Files                                    Decrypted Files


Android                                    ~/files/enc                                             ~/cache/dec

macOS                                      ~/temp/attachments                           ~/temp/preview

Windows                                 ~/temp/attachments                           ~/temp/preview

This behavior applies to files both sent and received.  Also keep in mind there is a probability that you may find encrypted files with no corresponding decrypted version.  This may be due to the message retention time expiring, which is why the order of examination is important, or it may mean the user never opened the file.

For both macOS and Windows, the only way to recover message content is via a manual examination using the Wickr UI, which means that a logical image should contain the sought after data.  However, the order of your examination can impact your ability to recover any decrypted files that may be present on the device.  Since the Wickr application is keeping track of what files may have passed their message retention period, it is extremely important to check for decrypted files prior to initiating Wickr on the device for a manual examination.  Failure to do so will result in any decrypted file whose message retention time has expired being deleted.

The Android database.  Slightly different

While the databases for macOS and Windows are inaccessible, the story is better for Android.  While conducting research for this post I discovered Cellebrite Physical Analyzer was not able to decrypt the wickr_db database even though it was prompting for a password.  Cellebrite confirmed Wickr had, in fact, changed their encryption scheme and Physical Analyzer was not able to decrypt the data.  A short time later they had a solution, which allowed me to proceed with this part of the post.  While not currently available to the public, this solution will be rolled out in a future version of Physical Analyzer.  Fortunately, I was granted pre-release access to this feature.

Again, thank you Heather and Or.  🙂

While there is still a good deal of data within the wickr_db file that is obfuscated, the important parts are available to the examiner, once decrypted.  The first table of interest is “Wickr_Message.”  See Figure 19.

Figure 19.png
Figure 19.  Wickr_Message table.

The blue box is the timestamp for sent and received message (Unix Epoch) and the orange box contains the text of the message or the original file name that was either sent or received by the device.  The timestamp in the red box is the time the message will be deleted from the Wickr UI and database.  The values in the purple box are inteteresting.  Based on testing, each file I sent or received had a value of 6000 in the messageType column.  While not that important here, these values are important when discussing iOS.

The blobs in the messagePayload column are interesting in that they contain a lot of information about file transfers between devices.  See Figure 20.

Figure 20.png
Figure 20.  Message payload.

The file sender can be seen next to the red arrow, the file type (e.g., picture, document, etc.) is next to the blue arrow, the GUID assigned to the file is seen in green box.  The GUID values can be matched up to the GUIDs of the files found in the /enc and /dec folders.  Here, the GUID in the green box in Figure 20 can be seen in both folders in Figure 21.  Finally, you can see the original name of the file next to the purple arrow (iOS_screenshot).  The original file name also appears in the cachedText colum in Figure 19.

Figure 21
Figure 21.  Matching GUIDs

The orange box in Figure 20 contains the recipients username along with the hash value of the recipient’s Wickr User ID.  That value can be matched up to the value in the senderUserIDHash column in the same table (see the red box in Figure 22).  The title of this column is deceptive, because it isn’t actually the userID that is represented.

Figure 21
Figure 22.  Sender’s hashed ID

Figure 23 shows the same hash in the serverIDHash column in the table Wickr_ConvoUser table.

Figure 23
Figure 23.  Same IDs.

Also of note in this table and the one seen in Figure 22 is the column vGroupID.  Based on testing, it appears every conversation is considered to be a “group,” even if that group only has two people.  For example, in my testing I only had my two test accounts that were conversing with each other.  This is considered a “group,” and is assigned a GUID (seen in the blue box).  The good thing about this value is that it is consistent across devices and platforms, which could come in handy when trying to track down conversation participants or deleted conversations (by recovering it from another device).  An example of this cross-platform-ing is seen in Figure 24, which shows the table ZSECEX_CONVO from the Wickr database in iOS.  Note the same GroupID.

Figure 24
Figure 24.  Same group ID.

Figure 25 shows, again, the serverIDHash, but this time in the table Wickr_User.  It is associated with the value userIDHash.  The value userAliasHash (the same table) is seen in Figure 26.

Figure 25
Figure 25.  serverIDHash and the userIDHash.
Figure 26
Figure 26.  userIDHash (Part 2).

Figure 27 shows some telemetry for the users listed in this table.

Figure 27
Figure 27.  User telemetry.

The columns isHidden (purple box) and lastMessaged (red box) are self-explanatory.  The value of 1 in the isHidden column means the user does not appear in the Conversations section of the UI.  That value coupled with the value of 0 in the lastMessaged column indicates this row in the table probably belongs to the logged in account.

The lastRefreshTime column (blue box) has the same value in both cells.  The timestamp in the cell for row 1 is when I opened the Wickr app, which, undoubtedly, caused the app to pull down information from the server about my two accounts.  Whether this is what this value actually represents requires more testing.  The same goes for the values in lastActivityTime column (orange box).  The value seen in the cell in row 1 is, based on my notes, the last time I pushed the app to the background.  The interesting thing here is there was activity within the app the after the timestamp (the following day around lunch time PDT).  More testing is required in order to determine what these values actually represent.  For now, I would not trust lastActivityTime at face value.

The table Wickr_Settings contains data of its namesake.  The first column of interest is appConfiguration (red box).  See Figure 28.

Figure 28.PNG
Figure 28.  Wick_Settings

The data in this cell is in JSON format.  Figure 29 shows the first part of the contents.

Figure 29
Figure 29.  JSON, Part 1.

There are two notable values here.  The first, in the blue box, is self explanatory:  locationEnabled (Wickr can use location services).  I let Wickr have access to location services during initial setup, so this value is set to ‘true.’  The value in the red box, alwaysReauthenticate, refers to the setting that determines whether or not a user has to login into Wicker each time the app is accessed.  It corresponds to the switch in the Wickr settings seen in Figure 30 (red box).

Figure 30.PNG
Figure 30.  Login each time?  No thanks.

Because I didn’t want to be bothered with logging in each time, I opted to just have Wickr save my password and login automatically each time, thus this value is set to ‘false.’  If a user has this set and does not provide the Wickr password, a manual examination will be impossible.

The rest of the contents of the JSON data are unremarkable, and is seen in Figure 31.

Figure 31
Figure 31.  JSON, Part 2.  Nothing much.

There are three additional columns that are notable in this table.  The first is the setting for the Secure Shredder, autoShredderEnabled.  This value is set to 1, which means that it is enabled.  I would not expect to see any other value in this cell as Secure Shredder runs automatically in Wickr Me and some tiers of the Wickr Pro versions; there is no way to disable it unless the Silver, Gold, or Enterprise versions of Wickr is present.  See Figure 32.

Figure 32
Figure 32.  Anonymous Notifications, Secure Shredder, and Auto Unlock.

The second notable column is unlockMessagesEnabled (red box).  As its name implies, this setting dictates whether a message is unlocked on receipt, or if a user has to manually initiate the unlock.  I took the default setting, which is not to unlock a received message (database value of 0).  Figure 33 shows the setting in the Wickr Settings UI.

Figure 33
Figure 33.  Message Auto Unlock switch.

Figure 32 also shows anonymousNotificationsEnabled (orange box).  This setting dictates whether Wickr notifications provide any specific information about a received message/file (e.g., sender’s user name, text of a message, file name), or if the notification is generic (e.g., “You have a new message”).  Again, the default is to show generic notifications (database value of 1).  Figure 34 shows the setting in the Wickr Settings UI.  Note the switch is off, but since I have Auto Unlocks disabled, this switch is not used because my messages are not automatically unlocked on receipt.

Figure 34.PNG
Figure 34.  Anonymous Notification setting.

I want to address one last table;  Wickr_Convo.  Using the conversation GUIDs, you can determine the last activity within each conversation that is stored on the device.  In Figure 35, this conversation GUID is the same as the ones seen in Figure 23 and 25.

Figure 35
Figure 35.  Conversations listed by GUID.

There are two values that are notable.  The first is is the lastOutgoingMessageTimestamp (red box). That is a pretty self-explanatory label, right?  Not quite, and examiners should be careful interpreting this value.  That same timestamp appears in the Wickr_Message table seen in Figure 37, but with a different label.

Figure 36
Figure 36.  Wickr_Convo table timestamps.
Figure 37.png
Figure 37.  Wickr_Message table timestamps.

It appears that the lastOutgoingMessageTimestamp from Wickr_Convo applies to the last message that did not involve a file transfer (value timestamp seen in the Wickr_Message table) .  The value lastUpdatedTimestamp (blue box in Figure 36) actually represents the last communication (message or file transfer) in the conversation, which is seen in the blue-boxed timestamp value in the Wickr_Message table (blue box in Figure 37).

The value messageReadTimestamp (orange box in Figure 36) represents the time the last message was unlocked.  Notice that the value is just about the same as that seen in lastUpdatedTimestamp, but with more granularity.

A couple more things

There are two more files I’d like to touch on with regards to the Android version.  The first is com.google.android.gms.measurement.prefs.xml found in the /shared_prefs folder.  See Figure 38.

Figure 38
Figure 38.  Measurement data for the app.

This file keeps track of certain data about app usage.  The most obvious data points are the install time for the app itself (orange box) and the first time the app was opened (red box).  The next two data poins are app_backgrounded (yellow box) and last_pause_time (green box).  The app_backgrounded value, as you can see, is a boolean value that indicates whether the app is active on the device screen or if the app is running in the background (i.e. not front-and-center on the device).  The value last_pause_time is the last time the app was pushed to the background by the user (“paused”).  If an examiner is pulling this data from a seized device is highly likely that the app_backgrounded value will be true, unless the device is seized and imaged while Wickr is actively being used.

The value in the blue box, last_upload, is a deceiving value, and I have yet to figure out what exactly it represents.  I have a theory that it may be the last time the app uploaded information about its current public key which is used in the asymmetric encryption operations during message transport, but I can not be totally sure at this point.  Just know that last_upload may not necessarily represent the last time a file was uploaded.

The last file is COUNTLY_STORE.xml.  Based on research, it appears this file may be used for analytical purposes in conjunction with the Countly platform.  This file keeps some metrics about the app, including the cell service carrier, platofrm version (SDK version), hardware information, and a unique identifier, which, on Android, is the advertising ID (adid).  The data appears to be broken up into transactions with each transaction containing some or all of the data points I just mentioned. Each transaction appears to be separated by triple colons.  Each also contains a timestamp.

A representitive example can be seen in Figure 39; it does not contain all of the data points I mentioned but it gives you a good idea as what to expect.

Figure 40
Figure 39.  COUNTLY_STORE.xml in Android.

This file is inconsistent.  On some of my extractions the file was empty after app use and on others it was full of data.  Sometimes the timestamps coincided with my being in the app, and others did not.  There does not seem to be enough consistency to definatively say the timestamps seen in this file are of any use to examiners.  If someone has found otherwise please let me know.

There is a iOS equivalent:  County.dat.  This file contains most of the same data points I already described, and while it has a .dat extension, it is a binary plist file.  In lieu of the adid (from Android), a deviceID is present in the form of a GUID.  I think this deviceID serves more than one purpose, but that is speculative on my part.

Speaking of iOS…

iOS is different. Of course it is.

The iOS version of Wickr behaves a little differently, probably due to how data is naturally stored on iOS devices.  The data is already encrypted, and is hard to access.  The two biggest differences, from a forensic standpoint, are the lack of decrypted versions of opened files, and the database is not encrypted.

Before I proceed any further, though, I do want to say thank you again to Mike Williamson for his help in understanding how the iOS app operates under the hood.  🙂

I searched high and low in my iOS extractions, and never found decrypted versions of files on my device.  So there are two possible explanations:  1, they are in a place I didn’t look (highly unlikely but not completely impossible), or 2, they are never created in the first place.  I’m leaning towards the latter.  Regardless, there are no decrypted files to discuss.

Which leaves just the database itself.  While it is not encrypted, a majority of the data writtent to the table cells is encrypted.  I will say I am aware of at least two mobile device forensic vendors, who shall not be named at this time, that will probably have support for Wickr on iOS in the near future.  In the meantime, though, we are left with little data to review.

The first table is ZWICKR_MESSAGE, and, as you can guess, it contains much of the same data as the Wickr_Message table in Android.  Remember when I mentioned the messageType value in Android?  In iOS that value is ZFULLTYPE.  See Figure 40.

Figure 38
Figure 40.  Type 6000.

The value of 6000 is seen here, and, as will be seen shortly, correspond to files that have been sent/received.  Also, note the Z_PK values 8 and 10, respectively, because they will be seen in another table.

Figure 41 shows some additional columns, the titles of which are self-explanatory.  One I do want to highlight, though, is the ZISVISIBLE column.  The two values in red boxes represent messages I deleted while within the Wickr UI.  There is a recall function in Wickr, but I was not able to test this out to see if this would also place a value of 0 in this column.

Figure 39.png
Figure 41.  Deleted message indicators.

Figure 42 shows another set of columns in the same table.  The columns ZCONVO and Z4_CONVO actually come from a different table within the database, ZSECEX_CONVO.  See Figures 42 and 43.

Figure 40.png
Figure 42.  Conversation and Calls.
Figure 41
Figure 43.  ZSECX_CONVO table.

In Figure 42 the two columns highlighted in the orange box, ZLASTCALLCONVO and Z4_LASTCALLCOVO, appear to keep track of calls made via Wickr; in my case these are audio calls.  Here, the value indicates the last call to take place, and what conversation it occured in.  This is interesting since the Android database did not appear to keep track of calls as far as I could tell (the data may have been encrypted).  Remember, this table is equivalent to the Wickr_ConvoUser table in the Android database, so you will be able to see the ZVGROUPID, shortly.

The next bit of the table involves identifying the message sender (ZUSERSENDER), the timestamp of the message (ZTIMESTAMP), the time the message will expire (ZCLEANUPTIME), and the message identifier (ZMESSAGEID).  The timestamps in this table are stored in Core Foundation Absolute Time (CFAbsolute).  See Figure 44.

Figure 42.png
Figure 44.  Messages and their times.

The values in the ZUSERSENDER column can be matched back to the Z_PK column in the ZSECX_USER table.

That’s it for this table!  The rest of the contents, including the ZBODY column, are encrypted.

The ZSECX_CONVO table has some notable data as seen in Figure 45.  The one column I do want to highlight is ZLASTTIMESTAMP, which is the time of the last activity (regardless of what it was) in the conversation (the “group”).  Interestingly, the times here are stored in Unix Epoch.

Figure 43.png
Figure 45.  Last time of activity in a conversation (group).

Figure 46 shows some additional data.  The last conversation in which a call was either placed or received is seen in the column ZLASTCALLMSG (orange box – timestamp can be gotten from the ZWICKR_MESSAGE table), along with the last person that either sent/received anything within the conversation  (ZLASTUSER – red box). The value in the ZLASTCALLMSG column can be matched back to the values in the Z_PK column in the ZWICKR_MESSAGE table.  The value in the ZLASTUSER column can be matched back to the Z_PK column in the ZSECX_USER table. And, finally, as I previously showed in Figure 24, the ZVGROUPID (blue box).

Figure 44
Figure 46.  The last of the ZSECX_CONVO table.

The table ZSECEX_USER, as seen in Figures 47 and 48, contains data about not only the account owner, but also about users who the account holder may be conversing with.  The table contains some of the same information as the Wickr_User table in Android.  In fact, Figure 47 looks very similar to Figure 27.  The values represent the same things as well.

Figure 47
Figure 47.  Hidden status and last activity time.

Figure 48 shows the same items as seen in Figure 26, but, as you can see, the hash values are different, which makes tracking conversation participants using this informaiton impossible.

Figure 48
Figure 48.  Same participants, different hashes.

File transfers in iOS are a bit tricky because some of the data is obfuscated, and in order to figure out which file is which an examiner needs to examine three tables:  Z_11MSG, ZWICKR_MESSAGE, and ZWICKR_FILE.  Figure 49 shows the Z_11MSG table.

Figure 49
Figure 49.  Z_11MSG.

The colum Z_13MSG refers to the ZWICKR_MESSAGE table, with the values 8 and 10 referring to values in the Z_PK column in that table.  See Figure 50.

Figure 50
Figure 50.  Trasferred files.

Obviously, associated timestamps are found in the same row further into the table.  See Figure 51.

Figure 51
Figure 51.  Timestamps for the transferred files.

The column Z_11Files in Figure 49 refers to the ZWICKR_FILE table.  See Figure 52.

Figure 52
Figure 52.  Files with their GUIDs.

The values in Z_11FILES column in Figure 49 refer the values in the Z_PK values seen in Figure 52.  Figure 53 shows the files within the file system.  As I previously mentioned, there are no decrypted versions of these files.

Figure 53
Figure 53.  The file GUIDs from the database table.

Figure 54 shows values ZANONYMOUSNOTIFICATION and ZAUTOUNLOCKMESSAGES values  from the ZSECEX_ACCOUNT table (the Android values were seen in Figure 32).  Both values here are zero meaning I had these features turned off.

Figure 54
Figure 54.  Anonymous Notification and Auto Unlock settings in iOS.

The last table I want to highlight is the ZSECX_APP table.  See Figure 55.

Figure 55
Figure 55.  Users and their associated app installations.

The values in the ZUSER column relate back to the values seen in the Z_PK column in the ZWICKR_USER table.  Each different value in the ZAPPIDHASH represents a different app install on a device.  For example, Test Account 1 appeared on four different devices (iPhone, iPad, Windows, macOS).  This means four different devices each with their own individual installation of Wickr, which translates to a different ZAPPIDHASH value for each individual device.  Knowing a user has multiple devices could be beneficial.  Warning:  be careful, because this isn’t the only way to interpret this data.

As part of the testing, I wanted to see if this value could change on a device, and, as it turns out, it can.  Test Account 2 was only logged in on the Pixel 3.  I installed the app, used it, pulled the data, wiped the Pixel and flashed it with a new install of Android, and then reinstalled Wickr.  I repeated those steps one more time, which means Wickr was installed on the same device three different times, and, as you can see, there are three different hash values for ZUSER 2 (Test Account 2).

The morale of this story is that while this value can possibly represent different devices where a user may be logged in, it actually represents instances of app installation, so be careful in your interpretation.

Conclusion

Wickr is a tough one.  This app presents all sorts of forensic challenges.  At the moment there is very little data that is recoverable, but some insights about communication and app usage can be gleaned from what little data is available.  Sometimes, files can be recovered, and that may be all an examiner/investigator needs.

The good news is, though, there is help on the horizon.