Home page logo
/

nanog logo nanog mailing list archives

Re: Security team successfully cracks SSL using 200 PS3's and MD5 flaw.
From: Marshall Eubanks <tme () multicasttech com>
Date: Sat, 3 Jan 2009 15:01:16 -0500


On Jan 3, 2009, at 12:46 PM, Frank Bulk wrote:

For me the MD5 hashes on file downloads are more valuable to ensure the package is accurate to a byte rather than to verify its authenticity or
integrity.

Wouldn't listing both SHA-1 and MD5 hashes for a file download assure almost complete confidence that the file is the original one? I don't think anyone has been able to create a duplicate file that generates the same SHA-1 *and*
MD5 hashes as the original file.

I would not be too sure. MD5 only makes one pass over the data.

Suppose that I find two messages, M1 and M2, that have the same MD5 hash - there are methods out there to do that.

M1 is the good message, M2 is the bad message.

Let "||" be the concatenation operator.

So, for any string S

M1||S and M2||S have the same MD5 hash.

So, if I can find an S such that the SHA-1 hash for M1||S and M2||S
are the same, the MD5 hashes for these messages will still be the same, and you
have your feared condition.

My understanding is that one type of collision search involves using an S
and trying to find collisions of
M1 and M2||S by varying S. Modifying this to a common S does
not seem that different, and I would not want to bet a lot on it being fundamentally much
more difficult. (It might be, it might not be, I have no idea, the
question is, how much are you willing to bet on it ?)

Regards
Marshall


Regards
Marshall



Frank

-----Original Message-----
From: Florian Weimer [mailto:fw () deneb enyo de]
Sent: Saturday, January 03, 2009 10:23 AM
To: Skywing
Cc: NANOG
Subject: Re: Security team successfully cracks SSL using 200 PS3's and MD5
flaw.

Then again, I just got yet another Debian DSA mail which has
plaintext download links for new binaries.  The integrity
verification mechanism for said binaries is, you guessed it:
PGP-signed md5sums.

I can assure you that you will continue to receive these messages for
a while (unless you unsubscribe from the relevant mailing lists).

Our rationale is that in order to carry out currently known attacks on
MD5, you need to create a twin of documents, one evil and one
harmless.  In Debian's case, we prepare the data we sign on our
trusted infrastructure.  If someone can sneak in an evil twin due to a
breach, more direct means of attack are available.

In practice, the download links themselves are the larger problem
because users might use them without checking anything.  Eventually,
they will go away, together with the MD5 hashes.  Newer versions of
APT also use the SHA-256 checksums embedded in the Release and
Packages files.






  By Date           By Thread  

Current thread:
[ Nmap | Sec Tools | Mailing Lists | Site News | About/Contact | Advertising | Privacy ]