Betrayed Spouses Club: July 2012

I hope you've read the Skype primer I posted a while back... Because now it is time to roll up our sleeves and get dirty!

Main.db

The main.db SQLite 3 file is the heart of Skype. The file is located in Windows 7 at C:\Users\WindowsUserName\AppData\Roaming\Skype\SkypeUserName and in Windows XP at C:\Documents and Settings\WindowsUserName\Application Data\Skype\SkypeUserName.

In my Computer Psuedo-Forensics & Tools post, I pointed out some helpful software; a SQLite database browser called, appropriately, SQLite Database Browser and a raw hexadecimal file editor called HxD Hex Editor. Both are free. The discussion below utilizes these tools.

SQLite is cool

The Skype tool (also Firefox and Chrome) utilize a lightweight SQL engine called SQLite 3. This enables the software to have a back-end platform which is light enough to be used on mobile devices. The PC based tools are using the same engine as the software is relatively standardized on the back-end to reduce the cost of maintenance and reducing development cost and time across platforms.

SQLite is an open standard and has extensive documentation. All SQLite formatted files have a header beginning "SQLite format 3".

From my earlier post on Skype:

"According to the SQLite3 documentation at www.sqlite.org:

A database file might contain one or more pages that are not in active use. Unused pages can come about, for example, when information is deleted from the database. Unused pages are stored on the freelist and are reused when additional pages are required.
This means when the user deletes records, they're marked inactive. NOT removed from the main.db file. The deleted records sit in unallocated memory. They are, however, overwritten with new data. This means you should copy that file ***now*** before any old data is truly gone. Once overwritten, it cannot be retrieved.

Using the HxD Hex Editor, you will be able to open that main.db file and translate the machine code to text. There will be plenty of garbage characters and the data will be in a somewhat random order. If you're lucky enough you will have been able to catch a good bit of data that the user believes they've deleted for good."

That's why SQLite is cool :)

Using Main.db

The main.db file is a SQLite database. Using SQLite Database Browser (or any other SQLite tools), you can open the "official" memory of the Skype program. The information you can retrieve from this file represent the data that has not been deleted or removed by the user.

Schema

The schema is the set of tables and indexes within the database file. It provides the structure of the database, the names of the tables, the fields (data items) within each table and a description of the field indicating what type of data is stored and whether it is a primary key (a unique, mandatory value). The indexes for the database are provided. These indexes are tools used by SQLite to speed up the execution of queries used to retrieve data.

Just because I like you here is a link to a spreadsheet containing the tables and indexes and a link to a spreadsheet containing the tables and data fields.

Tables

The following tables appear in the main.db schema. Each table on this list is linked to a spreadsheet with a description of the table's fields and data types.

So what?

The following tables are where you will find useful data...

Contacts

You'll find all of the user's contacts with their SkypeName, their DisplayName and any other details they've provided in their Skype profile (location, mobile #, etc)

Videos

You'll find a list of the user's video chats and a Convo_ID.
The Convo_ID will map to the Convo_ID in the Conversations and Participants tables.

SMSes

I have no experience with this table but I believe it is used to store SMS texts sent via Skype to a cell phone (a paid feature for Skype users)

CallMembers

Provides a list of all parties to a call (grouped by Call_Name).
Duration is provided per participant and a Video_Status is provided (I believe 3 = video call)

ChatMembers

Provides a list of members taking part in a chat (grouped by Chat_Name).
The Adder field provides the SkypeName of the user who added the participant to the chat.

Conversations

Provides a list of the conversations in which the user participated.
The Identity column provides the SkypeName of the participant or the Chat_Name for group chats/rooms.
The DisplayName field provides the participant's displayed name in Skype or the displayed title of the group chat/room.
The Creator column notes the creator of the group chat/room.
Timestamps are provided for Last_Activity, Inbox_Timestamp, Creation_Timestamp and more.

Participants

Provides a list of conversation participants grouped by the Convo_ID
The Adder field notes the SkypeName of the user who added the participant to the conversation
The Identity column provides the SkypeName of the participant.
Text, Voice and Video status fields are provided.

Calls

Provides the calls in which the user has participated.
Call_Name is provided and maps to the Call_Name column in the CallMembers table.
Timestamps for the calls and the Host of the call are provided.

Transfers

Provides the details of files shared and downloaded by the user.
Partner_Handle is the SkypeName of the other party, Partner_DisplayName is their DisplayName.
FileName and FileSize is provided along with the FilePath (uploads only I believe).
Convo_ID is provided which maps to the Participants and Conversations tables.
Timestamps are provided.

Voicemails

Lists voicemails sent to the user
Partner_Handle is the SkypeName of the other party, Partner_DisplayName is their DisplayName.
Path column displays a ".dat" file which is located in the ...\Skype\SkypeUserName\Voicemail folder

Chats

Provides the chats in which the user participated.
The Name field follows this structure; #SkypeUserNameOfInitiator/$SkypeUserNameOfPartner;ChatIDString

The ChatIDString is a 16-digit alphanumeric string that is unique to the Chat
The SkypeNameOfPartner is replaced with the ChatIDString when the chat is a group chat/room. Ex: #SkypeUserNameOfInitiator/$ChatIDString

The Friendly_Name column provides the display name of the partner or group chat/room.
The Adder field notes the SkypeName of the user who added the participant
Timestamps are provided
The Posters field is a concatenated list of SkypeUserNames that posted to the chat
The Participants field is a concatenated list of SkypeUserNames that received messages from the chat
The ActiveMembers field is a concatenated list of SkypeUserNames of those who have recently posted
The dbPath field displays a ".dat" file which is located in the ...\Skype\SkypeUserName\Chatsync folder

The name of the ".dat" file is a 16-digit alphanumeric
The first two characters indicate the subfolder where the ".dat" file is located under the Chatsync folder. Ex- if the dbPath field has the value of 01abc2345def6789.dat; the file is located at ...\Skype\SkypeUserName\Chatsync\01\

Messages

Provides a Convo_ID to map to Conversations table, Videos table and others.
Provides ChatName to map to the Name field in the Chats table.
Notes the SkypeName of the Author of the message.
Provides the message detail in the Body_XML field. This is the most important field... this is the message sent from one party to another!

Timestamps

The timestamps in main.db follow a format based on UNIX. You will need to convert these timestamps into a human-readable values. For example, the value '1325900664' represents January 6, 2012 8:44pm. I use the following equation in Excel to convert the dates (assuming the Timestamp value is in cell B3):

=IF(B3="","",(B3/86400)+25569+(-5/24))

The IF statement states that if there is no value for Timestamp, then no value should be returned. If there is a value in the Timestamp field, the equation should be executed.

In SQL queries the date is converted using the datetime function. The format of the function is as follows:

datetime(timestamp_field,'unixepoch')

A query to start off with

Not everyone can write SQL queries, but they should! Here is a simple sample query to get you on your way. This retrieves all contacts sorted by the number of times they appear in the participants table:

select c.skypename
         ,c.fullname
         ,c.country
         ,c.province
         ,c.city
         ,c.phone_home
         ,c.phone_office
         ,c.phone_mobile
         ,c.main_phone
         ,c.emails
         ,c.verified_email
         ,datetime(c.lastused_timestamp,'unixepoch') lastused_timestamp
         ,count(p.identity)
from contacts c
    ,participants p
where c.skypename = p.identity
group by c.skypename
         ,c.fullname
         ,c.country
         ,c.province
         ,c.city
         ,c.phone_home
         ,c.phone_office
         ,c.phone_mobile
         ,c.main_phone
         ,c.emails
         ,c.verified_email
         ,datetime(c.lastused_timestamp,'unixepoch')
order by count(p.identity) desc

What's the deal with Chatsync?

The Chatsync folders also contribute a great deal. The main.db database includes pointers to the ".dat" files in the Chat table. I believe that these folders within Chatsync are used to store nodes of information which is retrieved by the Skype application when the chat data is needed. It's sort of like an extended memory to save information about the chat. I do know the Chatsync files are not inclusive of all the information presented in the main.db Chat table and I have found data present in the Chatsync files not present in the main.db tables.

Forensics

Reading the Main.db file with a SQLite utility and the Chatsync files are of limited use when trying to recover data that has been deleted. As I stated in this earlier article, the best approach is to read Main.db with a hexadecimal reader to recover partial records of deleted messages, video calls, voice calls, chats and other data. The Chatsync files are of limited worth as these appeared, in my experience, to have been deleted with more regularity than the old data in main.db was overwritten by new data.

Other Tools

The other helpful tools to user are SkypeLogView and SkypeChatsyncReader. I discussed these in my earlier post:

SkypeLogView
The good people at NirSoft have provided a tool for analyzing the Skype database files for call logs, chats, etc. It is a very handy tool but much more data can be gathered using HxD.

SkypeChatsyncReader
A utility created by Rasmus Riis Kristensen from the Computer Crime Unit of Danish National Police. This tool reverse engineered the location of data in the .dat files of Skype.

Conclusion

The Main.db file is a useful source of data IF a deletion of data has not occurred. The presentation of files from a SQLite database browsing utility can provide a well-formatted view into Skype usage. Please remember that carving the Main.db file with a hex editor will yield data that has been deleted by the user. However the presentation of this deleted data is nowhere near the organized output of the Main.db file.

-- DNS

Betrayed Spouses Club

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Friday, July 20, 2012

Skype Main.db