On 2013/11/04 17:13, ToddAndMargo wrote: > On 11/04/2013 05:07 PM, Yasha Karant wrote: >> On 11/04/2013 04:53 PM, ToddAndMargo wrote: >>> On 11/04/2013 04:21 PM, Yasha Karant wrote: >>>> I need to do a media comparison between a data DVD and the .iso file >>>> that purportedly contains the image of the exact DVD (including any >>>> bootable or autoload binary files, not for an Intel instruction set >>>> architecture). >>>> >>>> When burning to the DVD, applications such as K3B and Nero (for Linux) >>>> will do a verify of the burned media. My understanding is that these >>>> applications go through the device driver and device controller >>>> hardware/firmware that may be applying error correction to the raw bit >>>> stream; any such detected "hardware media" errors typically are reported >>>> by the driver to a log file, but typically (if corrected) do not cause >>>> the application to fail. >>>> >>>> If one mounts the .iso file, by a command similar to that below, >>>> >>>> # mount -t iso9660 -o ro,loop=/dev/loop0 /files/dvdimage.iso >>>> /media1/virtualdisc >>>> >>>> and likewise has the physical DVD in the DVD drive and mounted from, >>>> say, /dev/sr0 >>>> >>>> will a diff /dev/loop0 /dev/sr0 suffice? >>>> >>>> Is there a utility that will do the same thing that Nero would do as it >>>> verifies after burning, but not requiring the burn -- that is, verify a >>>> DVD against an ISO image file? >>>> >>>> If /dev/sr0 were mounted on, say, /media/someDVD, and the ISO image >>>> file on >>>> /media1/virtualdisk , is there a utility or script to do a "bit by bit" >>>> comparison via the mount points (not just the "raw" mount as /dev/sr0 )? >>>> >>>> Yasha Karant >>>> >>> >>> >>> Hi Yasha, >>> >>> Check the DVD as a raw device. >>> >>> After you burn the ISO, eject the DVD (clears out something, >>> I don't know what, but had to learn the hard way): >>> /usr/bin/eject /dev/sr0 >>> >>> Then inject the DVD (close the door). Can be on the same >>> line. >>> /usr/bin/eject -t /dev/sr0 >>> >>> Then make an MD5SUM of each >>> md5sum /files/dvdimage.iso /dev/sr0 >>> >>> Eyeball the sums. One will be on top of the other. >>> >>> If you like, I have some leftover code I can send you. >>> >>> -T >>> >>> >> >> From http://en.wikipedia.org/wiki/Md5sum >> >> As with all such hashing algorithms, there is theoretically an unlimited >> number of files that will have any given MD5 hash. However, it is very >> unlikely that any two non-identical files in the real world will have >> the same MD5 hash, unless they have been specifically created to have >> the same hash. >> >> End quote. >> >> I explain the above reality to my students, although I do use MD5SUM >> myself. I was hoping for a utility that did a true bit-by-bit >> comparison of the two files. >> >> >> Aside: Note that a (very) clever attacker can embed specific issues >> into a file such that the corrupted (and perhaps infected) file will >> pass a MD5 hash test. Note that USA NSA and other entities often do >> employ such clever persons (do recall the cyber attack on the fissile >> material enrichment facilities of a Middle Eastern nation state not in >> full agreement with USA foreign policy, albeit an attack not >> specifically limited to this mechanism). I am not suggesting that the >> DVD and ISO image file I am using are subject to this sort of clever >> corruption; but, it is important to understand the limitations of >> certain techniques. >> >> Yasha Karant >> > > Hi Yasha, > > The likely hood is pretty low. > > You could always try using the SHA sums. Maybe do > both. > > -T Or use the "cmp" command, "cmp -l infile outfile" if he really wants a byte by byte comparison of the disks. {o.o}