On Wednesday 03 March 2010, Mike McCarty wrote: >Tim wrote: >> On Tue, 2010-03-02 at 20:24 -0500, Andre Robatino wrote: >>> I use the rawread script from >>> >>> http://www.troubleshooters.com/linux/coasterless.htm#rawread >>> >>> which automatically reads the correct size of the ISO, and runs a dd >>> command reading exactly that much off the disc. >> >> I have to ask: Why doesn't the installer's self test routine work that >> way? This problem has been around for *years*. > >How would you embed the checksum in the image, without knowing what >the image's checksum is? To put it another way, when you put the >checksum in the image, the checksum of the image changes due to >the embedding. Usually, with a ROM, say, one writes an image, and >computes the checksum in such a manner that by putting it into >the location reserved for it (which was originally filled with >all zeroes), the checksum of the whole image is zero. However, >this is only reasonable for small, not cryptographically secure, >checksums. It won't work for MD5 or SHA1, for example, because >there is no reasonable way to do it. That's what we mean by >"cryptographically secure". It isn't feasible. > >A smaller, and less robust checksum isn't adequate for checking >an image which is GB in size. A 16 bit CRC is ok for a 1MB ROM. >It isn't robust enough for a 5GB ISO image. > >Mike > Who said anything about embedding the checksum? What you do is note the size of the iso as it exists on your hard drive, divide that by the size of a cd or dvd blocksize, normally 2048 bytes, then divide the size of the iso using kcalc or whatever to tell you how many blocks to read from the optical disk, of size (bs=2048) and feed to sha(1|256)sum, or to md5sum, then cat the checksum file to the same window and see if they properly match. I have gone through 3 optical drives since I started using that method, and it works 100% of the time. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) "Are you sure you're not an encyclopedia salesman?" No, Ma'am. Just a burglar, come to ransack the flat." -- Monty Python -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines
