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#REDIRECT [[Shellcode#Alphanumeric]]
{{Original research|date=February 2008}}
{{R from merge}}
:''You may be looking for [[Character encoding]].''
:''or [[SYNOP]] and [[CLIMAT]] (alphanumeric codes used for meteorological and climatological data transmission)
In general, in [[computing]], an '''alphanumeric code''' is a series of letters and numbers (hence the name) which are written in a form that can be processed by a computer.
Specifically, in computer underground terminology, alphanumeric code is [[machine code]] that is written so that it assembles into entirely alphanumeric [[ASCII]] characters such as 0-9, A-Z and a-z<ref>{{cite web |last=SkyLined |url=http://skypher.com/wiki/index.php?title=X86_alphanumeric_opcodes |title=List of x86 Alphanumeric opcodes |publisher=Skypher.com}}</ref><ref>{{cite web |last=SkyLined |url=http://skypher.com/wiki/index.php?title=X64_alphanumeric_opcodes |title=List of x64 alphanumeric opcodes |publisher=Skypher.com}}</ref>. This type of encoding was created by [[Hacker (computer security)|hackers]] to be able to pass machine code through a filter that removes any non-alphanumeric character and still be able to have it perform its intended tasks successfully. (Because normal machine code frequently uses non-alphanumeric characters, these would get removed by such a filter and the code would not be able to pass the filter without being modified to the point where it no longer works). A slightly less restrictive form of this type of encoding is printable code, which uses all [[Control character|printable]] characters such as 0-9, A-Z, a-z, !@#%^&*() etc...
Writing alphanumeric or printable codes require good understanding [[instruction set architecture]] of the machine on which the code is to be executed.
==See also==
*[[EICAR test file]] - a test pattern used to test the installation of the anti virus software, which is written in printable code.
==External links==
* [http://www.phrack.org/issues.html?issue=57&id=15#article Writing ia32 alphanumeric shellcodes], an article on how to write alphanumeric shellcode.
* [http://www.phrack.org/issues.html?issue=61&id=11#article Building IA32 'Unicode-Proof' shellcodes], an article on how to write Unicode proof shellcode.
* [http://skypher.com/wiki/index.php?title=Www.edup.tudelft.nl/~bjwever/whitepaper_shellcode.html.php Writing IA32 restricted instruction set shellcodes], an article on how to write code that is very limited in the number of characters it can use (such as alphanumeric code).
* [http://skypher.com/wiki/index.php?title=Www.edup.tudelft.nl/~bjwever/documentation_alpha2.html.php ALPHA2], an alphanumeric shellcode encoder: Utility to encode normal machine code into alphanumeric (upper-case or mixed-case) ASCII or Unicode text
* [http://www.vividmachines.com/shellcode/shellcode.html#ps Shellcoding for Linux and Windows — Printable Shellcode]: Explanation and tutorial
== References ==
{{reflist}}
[[Category:Computer security exploits]]
[[ca:Alfanumèric]]
[[es:Códigos alfanuméricos]]
[[pl:Kod alfanumeryczny]]
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