WINDOWS FORENSIC

Registry Examination

The Windows Registry is a hierarchical database that stores configuration settings and options on Microsoft Windows operating systems. It contains settings for low-level operating system components and for applications running on the platform that have opted to use the registry. The kernel, device drivers, services, SAM, user interface and third party applications can all make use of the registry. The registry also provides a means to access counters for profiling system performance.

Structure

Keys and values

The registry contains two basic elements: keys and values. Registry keys are container objects similar to folders. Registry values are non-container objects similar to files. Keys may contain values or further keys. Keys are referenced with a syntax similar to Windows' path names, using backslashes to indicate levels of hierarchy. Keys must have a case insensitive name without backslashes.


The hierarchy of registry keys can only be accessed from a known root key handle (which is anonymous but whose effective value is a constant numeric handle) that is mapped to the content of a registry key preloaded by the kernel from a stored "hive", or to the content of a subkey within another root key, or mapped to a registered service or DLL that provides access to its contained subkeys and values.

E.g. HKEY_LOCAL_MACHINE\Software\Microsoft\Windows refers to the subkey "Windows" of the subkey "Microsoft" of the subkey "Software" of the HKEY_LOCAL_MACHINE root key.


There are seven predefined root keys, traditionally named according to their constant handles defined in the Win32 API, or by synonymous abbreviations (depending on applications):


    HKEY_LOCAL_MACHINE or HKLM
    HKEY_CURRENT_CONFIG or HKCC (only in Windows 9x/Me and NT-based versions of Windows)
    HKEY_CLASSES_ROOT or HKCR
    HKEY_CURRENT_USER or HKCU
    HKEY_USERS or HKU
    HKEY_PERFORMANCE_DATA (only in NT-based versions of Windows, but invisible in the Windows Registry Editor)
    HKEY_DYN_DATA (only in Windows 9x/Me, and visible in the Windows Registry Editor)


Like other files and services in Windows, all registry keys may be restricted by access control lists (ACLs), depending on user privileges, or on security tokens acquired by applications, or on system security policies enforced by the system (these restrictions may be predefined by the system itself, and configured by local system administrators or by domain administrators). Different users, programs, services or remote systems may only see some parts of the hierarchy or distinct hierarchies from the same root keys.

Registry values are name/data pairs stored within keys. Registry values are referenced separately from registry keys. Each registry value stored in a registry key has a unique name whose letter case is not significant. The Windows API functions that query and manipulate registry values take value names separately from the key path and/or handle that identifies the parent key. Registry values may contain backslashes in their names, but doing so makes them difficult to distinguish from their key paths when using some legacy Windows Registry API functions (whose usage is deprecated in Win32).


The terminology is somewhat misleading, as each registry key is similar to an associative array, where standard terminology would refer to the name part of each registry value as a "key". The terms are a holdout from the 16-bit registry in Windows 3, in which registry keys could not contain arbitrary name/data pairs, but rather contained only one unnamed value (which had to be a string). In this sense, the entire registry was like a single associative array where the registry keys (in both the registry sense and dictionary sense) formed a hierarchy, and the registry values were all strings. When the 32-bit registry was created, so was the additional capability of creating multiple named values per key, and the meanings of the names were somewhat distorted.[4] For compatibility with the previous behavior, each registry key may have a "default" value, whose name is the empty string.


Each value can store arbitrary data with variable length and encoding, but which is associated with a symbolic type (defined as a numeric constant) defining how to parse this data.


Service provider logs

Although not technically part of mobile device forensics, the call detail records (and occasionally, text messages) from wireless carriers often serve as "back up" evidence obtained after the mobile phone has been seized. These are useful when the call history and/or text messages have been deleted from the phone, or when location-based services are not turned on. Call detail records and cell site (tower) dumps can show the phone owner's location, and whether they were stationary or moving (i.e., whether the phone's signal bounced off the same side of a single tower, or different sides of multiple towers along a particular path of travel).[7] Carrier data and device data together can be used to corroborate information from other sources, for instance, video surveillance footage or eyewitness accounts; or to determine the general location where a non-geotagged image or video was taken.


The European Union requires its member countries to retain certain telecommunications data for use in investigations. This includes data on calls made and retrieved. The location of a mobile phone can be determined and this geographical data must also be retained. In the United States, however, no such requirement exists, and no standards govern how long carriers should retain data or even what they must retain. For example, text messages may be retained only for a week or two, while call logs may be retained anywhere from a few weeks to several months. To reduce the risk of evidence being lost, law enforcement agents must submit a preservation letter to the carrier, which they then must back up with a search warrant.


Forensic process

The forensics process for mobile devices broadly matches other branches of digital forensics; however, some particular concerns apply. Generally, the process can be broken down into three main categories: seizure, acquisition, and examination/analysis. Other aspects of the computer forensic process, such as intake, validation, documentation/reporting, and archiving still apply.


Seizure

Seizing mobile devices is covered by the same legal considerations as other digital media. Mobiles will often be recovered switched on; as the aim of seizure is to preserve evidence, the device will often be transported in the same state to avoid a shutdown, which would change files.In addition, the investigator or first responder would risk user lock activation.


However, leaving the phone on carries another risk: the device can still make a network/cellular connection. This may bring in new data, overwriting evidence. To prevent a connection, mobile devices will often be transported and examined from within a Faraday cage (or bag). Even so, there are two disadvantages to this method. First, it renders the device unusable, as its touch screen or keypad cannot be used. Second, a device's search for a network connection will drain its battery more quickly. While devices and their batteries can often be recharged, again, the investigator risks that the phone's user lock will have activated. Therefore, network isolation is advisable either through placing the device in Airplane Mode, or cloning its SIM card (a technique which can also be useful when the device is missing its SIM card entirely).
Acquisition

The second step in the forensic process is acquisition, in this case usually referring to retrieval of material from a device (as compared to the bit-copy imaging used in computer forensics).

Due to the proprietary nature of mobiles it is often not possible to acquire data with it powered down; most mobile device acquisition is performed live. With more advanced smartphones using advanced memory management, connecting it to a recharger and putting it into a faraday cage may not be good practice. The mobile device would recognize the network disconnection and therefore it would change its status information that can trigger the memory manager to write data.

Most acquisition tools for mobile devices are commercial in nature and consist of a hardware and software component, often automated.

Examination and analysis

As an increasing number of mobile devices use high-level file systems, similar to the file systems of computers, methods and tools can be taken over from hard disk forensics or only need slight changes.

The FAT file system is generally used on NAND memory. A difference is the block size used, which is larger than 512 bytes for hard disks and depends on the used memory type, e.g., NOR type 64, 128, 256 and NAND memory 16, 128, 256, or 512 kilobyte.

Different software tools can extract the data from the memory image. One could use specialized and automated forensic software products or generic file viewers such as any hex editor to search for characteristics of file headers. The advantage of the hex editor is the deeper insight into the memory management, but working with a hex editor means a lot of handwork and file system as well as file header knowledge. In contrast, specialized forensic software simplifies the search and extracts the data but may not find everything. AccessData, Sleuthkit, and EnCase, to mention only some, are forensic software products to analyze memory images.Since there is no tool that extracts all possible information, it is advisable to use two or more tools for examination. There is currently (February 2010) no software solution to get all evidences from flash memories.



Data acquisition types

Mobile device data extraction can be classified according to a continuum, along which methods become more technical and "forensically sound," tools become more expensive, analysis takes longer, examiners need more training, and some methods can even become more invasive.



Manual acquisition

The examiner utilizes the user interface to investigate the content of the phone's memory. Therefore the device is used as normal, with the examiner taking pictures of each screen's contents. This method has an advantage in that the operating system makes it unnecessary to use specialized tools or equipment to transform raw data into human interpretable information. In practice this method is applied to cell phones, PDAs and navigation systems.[14] Disadvantages are that only data visible to the operating system can be recovered; that all data are only available in form of pictures; and the process itself is time-consuming.

Logical acquisition

Logical acquisition implies a bit-by-bit copy of logical storage objects (e.g., directories and files) that reside on a logical store (e.g., a file system partition). Logical acquisition has the advantage that system data structures are easier for a tool to extract and organize. Logical extraction acquires information from the device using the original equipment manufacturer application programming interface for synchronizing the phone's contents with a personal computer. A logical extraction is generally easier to work with as it does not produce a large binary blob. However, a skilled forensic examiner will be able to extract far more information from a physical extraction.

File system acquisition

Logical extraction usually does not produce any deleted information, due to it normally being removed from the phone's file system. However, in some cases -- particularly with platforms built on SQLite, such as iOS and Android -- the phone may keep a database file of information which does not overwrite the information but simply marks it as deleted and available for later overwriting. In such cases, if the device allows file system access through its synchronization interface, it is possible to recover deleted information. File system extraction is useful for understanding the file structure, web browsing history, or app usage, as well as providing the examiner with the ability to perform an analysis with traditional computer forensic tools.

Physical acquisition

Physical acquisition implies a bit-for-bit copy of an entire physical store (e.g. flash memory); therefore, it is the method most similar to the examination of a personal computer. A physical acquisition has the advantage of allowing deleted files and data remnants to be examined. Physical extraction acquires information from the device by direct access to the flash memories.

Generally this is harder to achieve because the device original equipment manufacturer needs to secure against arbitrary reading of memory; therefore, a device may be locked to a certain operator. To get around this security, mobile forensics tool vendors often develop their own boot loaders, enabling the forensic tool to access the memory (and often, also to bypass user passcodes or pattern locks).

Generally the physical extraction is split into two steps, the dumping phase and the decoding phase.


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