Steganography

OutGuess

• OutGuess is a steganography tool developed by Niels Provos.
• Quite secure, although some attacks exist.
• Package available for Windows, Linux, Cygwin...
• OutGuess works by storing information in the LSB of non-zero DCT coefficient, while preserving first-order statistics.

Patch on OutGuess 0.2

• There is a small bug in OutGuess 0.2 that makes estimate of the correctable message size to be negative for big images. Here's a patch that correct this.

--- outguess-0.2/jpg.c       2001-02-13 01:29:07.000000000 +0100
+++ outguess-0.2/jpg.c       2009-08-25 16:06:05.242378300 +0200
@@ -176,7 +176,7 @@
                        fprintf(stderr, "Can not calculate estimate\n");
                        res = -1;
                } else
-                       res = 2*bitmap->bits*b/(a + b);
+                       res = 2*(long long)bitmap->bits*b/(a + b);         /* Fixed: multiply was overflowing for big images */

                /* Pending threshold based on frequencies */
                for (i = 0; i < DCTENTRIES; i++) {

• To apply the patch on Cygwin, first fetch Outguess-0.2

$ /setup.exe&                               #Select Outguess-0.2 sources
$ cd /usr/src
$ cat > outguess-0.2.patch                  #Copy patch above in patch file
$ ./outguess-0.2-1.sh -v -c prep conf
$ patch -lNp0<outguess-0.2.patch            #Apply the patch
$ ./outguess-0.2-1.sh -v -c make install
$ cp -rv outguess-0.2/.inst/* /             #Install