Thursday, February 5, 2009

Strings and update

Its been a while since I posted anything so I wanted to get something up here.

First, in my last post I mentioned how I use the strings utility when analyzing binaries. The utility will allow you to view embedded strings within a binary. By default, it only shows ASCII strings. The problem with this is that in Windows binaries, there are usually embedded strings encoded in UNICODE, and by default, strings will not show them. To get around this, I was using SysInternal's strings utility with wine on my Linux system.

However, in a comment craigb stated that you can change the encoding strings looks for with the -e option. Here is a snippet from the strings man page:
-e encoding
Select the character encoding of the strings that are to be found.
Possible values for encoding are: s = single-7-bit-byte characters
(ASCII, ISO 8859, etc., default), S = single-8-bit-byte characters,
b = 16-bit bigendian, l = 16-bit littleendian, B = 32-bit bigen-
dian, L = 32-bit littleendian. Useful for finding wide character
By running strings using different encodings both ASCII and UNICODE strings in a Windows binary can be found. To do so, I whipped up a little Bash script which I now use whenever I want to pull strings from a binary:


(strings -a -t x $1; strings -a -e l -t x $1) | sort
The script, which I named mystrings, takes the file to scan as a command line option. It then runs strings against it two times - the first time looking for ASCII strings and the second looking for UNICODE (16-bit little endian actually) strings. The -t x options prints the hex offset of the string within the file. After the strings commands run, they are run through the sort program and displayed.

My concern with this was the Linux strings would miss something that the SysInternal's strings would pick up. So, I ran a test where both programs were run against the same file. The output was the same! Woohoo!

In other news, I'd like to announce I got a new job starting at the beginning of the year (which is pretty much the reason I have not been posting). Those who know me know where I went to, so I won't go into details here. However, I've gotten into my groove and should be posting more soon.

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