DISQUS

Creeva's World 2.0: Why I Hate MD5 or: How I Learned to Start Worrying and Hate the Misconceptions | Creeva's World 2.0

  • fung-li · 1 year ago
    there is a difference between md5 and the common practice to use only the contents of a file as input. i guess this is because the tool md5sum takes a filename as argument, which is like a shortcut of "cat file | md5sum". you could echo the filename and its contents and pipe it into md5sum, you would have it.

    so the better title would be "why i hate the practice of only using file-contents as input for md5 hashes and not taking the filename itself into account"
  • creeva · 1 year ago
    Well there was alot of people ignorant like me - so i thought the misconception title was best. But yes i hate the fact it ignores the file name
  • grin · 10 months ago
    It takes, say, 2 minutes to write a program which actually uses file metadata (name, creation and modification date, or even inode data [position on the disk]) for generating hashes, be it md5 (which in fact harder to spoof than you suggest) or some other algos (sha2 comes to mind). Takes half an hour if you want it a bit faster. :-)

    But your problem is that you fail to know the goal of the method you use: it's for detecting changes in the files (or, actually, the falsification of the data) and not to have a hash unique to the (actually any random) file. Downloaders aren't intersted whether the file is called "kernel-latest.tar.bz2" or "linux-2.6.31rc2.tar.bz2" as long as it's the same.

    Actual security tools (like tripwire, integrit, etc) use file metadata hashing as well, so they detect not just data or filename change, but moving the file or having it changed by any unknown means (which changes, say, inode numbers).

    Use tools what they're for. Don't try to screw in a screw with a sledgehammer. ;-)
  • creeva · 10 months ago
    btw the script I ended up writing with md5 did use some file metadata so yes you are write and it does take less then 2 minutes.
  • creeva · 10 months ago
    I was just pointing out the fallacy where some people take with MD5 - I'm well aware these days not to trust it too much . It has it's flaws and I know it is difficult to spoof - but MD5 collisions caused the new SSL vulnerability issue because people put trust in it and didn't think md5 collisions would be an issue at. It was considered good enough - if you find something you consider a problem raise awareness - in security "good enough" is never good enough - the bad guys always work past it.