The RAM disk maintains data when there is power and on warm boots.
On cold boots, the data in the RAM is completely wiped. EPOC is versatile in both its usage and licensing. Thus, when referring to EPOC features one must often do so in reference to a particular implementation. Hardware resources such as the system RAM are isolated from applications via a privilege boundary. The CPU will only perform privileged instructions for the kernel. All other user-mode applications that need access to hardware resources must access them via the kernel.
Kernel APIs allow such applications to remain on the unprivileged side of the boundary, while the kernel performs the necessary privileged commands. Finally, executables on Psion devices can be divided into two categories, applications and servers. Applications contain a user interface and, when executed, run in a separate process space. Thus, the system creates a virtual address space for each executed application.
In this way, traditional applications cannot accidentally overwrite data area of another application. The MMU, Memory Management Unit, manages the separate process spaces so writable memory of one application is not accessible by an another process. A server is an executable without a user interface. Servers generally provide APIs for clients clients can be applications or other servers. Some servers actually use the same process. It was designed by to be an operating system that contained a subset of the Win32 API.
The requirements were the operating system should be for small ROM-based systems. Thus, the resultant executable may actually differ depend-ing on the target CPU. Windows CE programming can be considered similar to Windows programming just with a subset of APIs and potentially reduced hardware resources no hard disk, and available RAM. Since Windows malware is possible, Windows CE malware is, of course, also possible.
However,current Windows malware is often specific to the particular Windows operating system. For example, many viruses take advantage of specific undocumented kernel features of Windows NT, which do not exist in Windows CE. In addition, Trojan horses often make Registry key changes, which also do not exist under Windows CE. Unfortunately, analogous features can all be found in Windows CE. For example, malware often utilizes the Run Registry keys of Windows 9x. Following is a brief description of the potential vectors of delivery foreach device.
All three operating systems have associated syncing applications. Syncing functionality is used primarily to synchronize data stored on the device with data stored on the desktop computer, back up data to the desktop computer, manage files, and install new device applications that are located on the desktop computer. Currently, this provides the easiest means of introducing malicious code.
For example, to install a new program on the Palm, one may download the new program from the Internet and save it to their desktop computer. Then, using the HotSync functionality, the program is transferred from their desktop computer to the Palm. Now saved to the Palm, the user can run the new program. In addition, the syncing functionality allows custom applications on a desktop PC to connect and manipulate data on PDAs. Such programmability provides the ability of malware to potentially send mail and manipulate files on the device from the desktop computer and vice versa.
Fortu-nately, this is not only advantageous for malware, but for potentially anti-virus solutions as well, both of which will be discussed later. Such capabilities are generally compliant with IrDA Infrared Data Association specifications and thus, one can easily interface with the IR capabilities of the device. However, the majority of devices utilize an associated application to allow the transfer of data via the IR port. For example, the PalmOS Exchange Manager provides a simple interface for PalmOS applications to send and receive data from a remote device using standard protocols.
In addition, low level access is obtained through the use of document APIs. With IR capabilities, devices are able to receive and send applications and thus, potentially malicious code. Currently, devices are designed to trigger an incoming data alert message how-ever, this message can be disabled. Disabling such a message requires specific agent code on the receiving device. Via IR, malicious programs could potentially speak to other infected devices exchanging information and code, all unbeknownst to users.
By adding optional modem hardware to the device or utilizing newer wireless models, one has access to standard Internet protocols.
Power of Capturing the Moment in Mobile Devices
In general, email access with attachments is available as is Web browsing. One can easily receive emails with executables attached, save those attachments, and run them. Such applications can easily contain malicious code. Devices generally contain pre-installed mail clients, which are also programmable.
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So, malicious software writers may only need to interface with existing mail clients rather than creating their own network-capable agent. A third party program can interact with the programs through a standard application-programming interface. Psion devices contain a client-server architecture, which allows one applications to speak to another, Windows CE applications generally utilize common APIs such as MAPI, and Palm applications can send launch codes to each other.
Using launch codes an application can direct another application to perform some action or modify its data. For example, in PalmOS, a malicious program could send a launch code to query all the email addresses in the Address List application. Then, the same program could send a launch code instructing the email application to queue and send email messages with itself as an attachment.
Threats to PDAs
How far and how fast such threats may spread is discussed later. The file streaming functions allow one to read, write, seek to a specified offset, truncate, and do everything else you would expect to do with a desktop-style file. Such functionality is all that is needed for a viral threat to spread.
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In all three operating systems, viral threats may find other applications on the device, append themselves to those applications, and change the entry point of the program to ensure future execution and continued replication. The Palm and some Windows CE and Psion implementations do not employ any inherent access control to applications and data files. System applications are easily modified as regular user applications.
This allows malicious code to not only modify some system files, but also destroy some system files. With a single click, one could wipe out all the applications and data on their device. Luckily, most devices contain sensitive information on the ROM, which is not writable. How-ever, the amount of middleware or built-in applications that exist on the ROM vary with each operating system and further depending on OEMs for each device. Since, sensitive system information is generally stored on the ROM, uses can reset or cold boot their devices losing applications and data, but still containing a functional PDA.
Then, potentially the user can re-store their applications and data via synchronization. All provide communica-tion libraries, which pose the greatest risk. Such libraries make programming high-level threats very easily. Without low-level knowledge of IR communications, one can easily create an agent to monitor incoming IR data requests. Net-work libraries allow programmers to create Berkeley-style sockets network programs. Such programs could range from a small SMTP engine, creating email capabilities on a device that may not even have a mail client, to a server listening for incoming commands acting as a remote access Trojan.
In addition, script languages are available on the Psion and some Windows CE devices. Creating programs in script languages is traditionally easier. A were both coded in script languages. By default, Psion for example, offers a script language known as OPL and Windows CE, depending on applications installed, can host a range of other potential script languages for creations of malware. One should not be surprised if a malicious threat is discovered tomorrow; however, one should be surprised if such a threat posed an immediate widespread threat.
In addition, at this moment the number of net-work connected PDA users is also magnitudes lower than the number of people with access to email. Secondly, if the number of PDA users increases, the number of different operating systems and their customizations still decreases the ability for a threat to spread effectively to anything other than a smaller subset of PDA users. Thus, a malicious personal digital worm would not spread nearly as fast as a Windows worm. Finally, the model of data exchange for PDAs is still asymmetric. Users still download applica-tion and data from a few primary sources rather than all PDA users exchanging information with all other PDA users.
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It is this symmetric nature of code exchange that can dramatically increase the threat of viral spread as seen with macro viruses. In addition, some OSes contain further hurdles, which may limit spread. These UIDs must be obtained from Symbian and thus could potentially be traceable to a particular individual or computer. So, in order for PDA malware to spread, the cost of PDAs will need to continue to decrease and become standard productivity devices issued in the corporate space. Also, vendors will need to standardize protocols, be cannibalized by market competition, or a clear market leader will need to emerge.
Only then does the threat increase dramatically.
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