Alphanumeric shellcode

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. This type of encoding was created by 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 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

• Writing ia32 alphanumeric shellcodes, an article on how to write alphanumeric shellcode.
• Building IA32 'Unicode-Proof' shellcodes, an article on how to write Unicode proof shellcode.
• 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).
• ALPHA2, an alphanumeric shellcode encoder: Utility to encode normal machine code into alphanumeric (upper-case or mixed-case) ASCII or Unicode text
• Shellcoding for Linux and Windows — Printable Shellcode: Explanation and tutorial