Forensic Disk Differencing
Forensic Disk Differencing is the process of taking two or more disk images from the same computer and determining what changes in the first disk image might have resulted in the changes that are observed in the second. One common use of differencing is to determine what an attacker did during a break-in. To be used for this purpose, it is necessary to have a forensic disk image of the computer before the break-in and after the break-in.
idifference.py is part of the Digital Forensics XML Python Toolkit distributed with fiwalk. This tool will compare two different disk images and report changes in files between the first and the second. It also produces a timeline of changes.
For example, using the nps-2009-canon2 series of disk images:
$ python idifference.py /nps-2009-canon2-gen2.raw nps-2009-canon2-gen3.raw >>> Reading nps-2009-canon2-gen2.raw >>> Reading nps-2009-canon2-gen3.raw Disk image:/corp/drives/nps/nps-2009-canon2/nps-2009-canon2-gen3.raw New Files: 2008-12-23 14:26:12 1315993 DCIM/100CANON/IMG_0041.JPG Deleted Files: 2008-12-23 14:12:38 855935 DCIM/100CANON/IMG_0001.JPG 2008-12-23 14:22:38 1347778 DCIM/100CANON/IMG_0037.JPG Files with modified content (but size unchanged): Files with changed file properties: DCIM/CANONMSC/M0100.CTG SHA1 changed 69b30c352ee802f49b1ea25325af9fa05c3ffca1 -> baa42c03a917b01b212fb7e538e5deb525995f31 DCIM/CANONMSC/M0100.CTG crtime changed to 1230070924 -> 1230071142 DCIM/CANONMSC/M0100.CTG mtime changed to 1230070924 -> 1230071142 DCIM/CANONMSC/M0100.CTG resized 180 -> 188 Timeline 2008-12-23 14:25:42 DCIM/CANONMSC/M0100.CTG SHA1 changed 69b30c352ee802f49b1ea25325af9fa05c3ffca1 -> baa42c03a917b01b212fb7e538e5deb525995f31 2008-12-23 14:25:42 DCIM/CANONMSC/M0100.CTG crtime changed 1230070924 -> 1230071142 2008-12-23 14:25:42 DCIM/CANONMSC/M0100.CTG mtime changed 1230070924 -> 1230071142 2008-12-23 14:25:42 DCIM/CANONMSC/M0100.CTG resized 180 -> 188 2008-12-23 14:26:12 DCIM/100CANON/IMG_0041.JPG created $
Here are some more examples: