XORSearch is a program to search for a given string in an XOR or
ROL encoded binary file. An XOR encoded binary file is a file where
some (or all) bytes have been XORed with a constant value (the key).
A ROL (or ROR) encoded file has it bytes rotated by a certain number
of bits (the key). XOR and ROL/ROR encoding is used by malware
programmers to obfuscate strings like URLs.

XORSearch will try all XOR keys (0 to 255) and ROL keys (1 to 7)
when searching. I programmed XORSearch to include key 0, because
this allows to search in an unencoded binary file (X XOR 0 equals
X).

If the search string is found, XORSearch will print it until the 0
(byte zero) is encountered or until 50 characters have been printed,
which ever comes first. 50 is the default value, it can be changed
with option -l. Unprintable characters are replaced by a dot.

WWW: http://blog.didierstevens.com/programs/xorsearch/