“Alice Falbala is given full access to all confidential and secret information about GAUL. Sincerely, Julius Caesar”
md5sum – a25f7f0b29ee0b3968c860738533a4b9
Comparing files letter_of_rec.ps and ORDER.PS
00000053: 97 17
0000006D: A3 23
0000006E: 78 79
0000007B: 5A DA
00000093: C8 48
000000AD: D8 58
000000BB: 6F EF
This is an interesting attack. You’ll notice that the above bytes differ by only a single bit, and that there are only seven of them….that suggests that it is also concievable that this could easily be expanded to a class of attacks based on the same principle.
It also exploits some conditionality in the .ps format to achieve the switching of the percieved content – anyone examining the actual source of either file would see that something was amiss, but why would you examine the source?
Anyone using MD5 in security critical applications should have stopped a long time ago, this is the final nail in its coffin. And I doubt it would be difficult to expand this attack to SHA1, since they’re quite close relatives (but I don’t yet understand the details of the attack, so thats just a gut feel rather than an informed statement).
Edit: Its worse than that – you can just take the file(s) they’ve made and insert your content where Alices two letters currently live, you don’t even need to be cryptographically clever to exploit this vulnerability.