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Re: Security team successfully cracks SSL using 200 PS3's and MD5
From: Brian Keefer <chort () smtps net>
Date: Sun, 4 Jan 2009 13:02:06 -0800

On Jan 4, 2009, at 12:05 PM, Joe Greco wrote:

The opinions on whether or not it is necessary to replace certs seems to vary depending on whose opinion you're listening to, but a relatively safe rule of thumb for this sort of security issue is to take the path that is most likely to avoid risk, which would seem to be replacing certs. To the extent that VeriSign is already doing this, it would seem that there is a
certain level of agreement with that assessment.

I would attribute that much more to desire to avoid the risk of bad PR, rather than the risk that it's possible to clone existing certs.

"SSL is cracked, VeriSign to blame!" was pretty much the top security story for several days. They had to do something to turn around the perception, despite accurate analysis and publications by organizations such as Microsoft. Perception is reality, and regardless of the technical merits, a significant amount of people seemed to believe that any certificates that mentioned MD5 anywhere in them are at risk of some unknown, but really scary Badness(tm).

I agree with VeriSign that offering to reissue certs is the smartest business decision they can make, considering their tagline is "The Value of Trust". I disagree that it was technically necessary.

Reissuing existing certificates signed by MD5 accomplishes nothing. Participation is voluntary, so if someone had managed to create a rogue CA, they certainly would not voluntarily destroy it by having their cert reissued! Technically the only thing necessary to prevent this attack has already been done, and that is to stop issuing certs signed with MD5 so that no one else can create a rogue CA via this means.

If they truly believed that there was a risk anyone else had done this already, they would need to revoke the CA cert, i.e. every vendor who shipped their CA cert in the default trusted issuer bundle would need to remove or invalidate it with a software update, but that would break _all_ the valid certificates signed by the CA. In order to do that, they would need to proactively contact every customer with a valid cert to make sure they were updated. What percentage of their customers do you think they would be able to reach (haven't changed contact information, etc)? How many application vendors would actually remove the old CA and add the new one in a timely manner? How many of those vendors' customers would actually upgrade to the new version?

So they've done what they need to in order to prevent future exploits, and obviously they aren't that worried that the exploit has actually been performed maliciously in the past. Offering to reissue existing certs is a PR smokescreen (although a necessary one).

I think there's a huge fundamental misunderstanding. It seems that the popular belief is that it's possible to use an existing MD5 signature for any evil bits that you choose, which is not the case. The actual exploit in this case is the ability to "unlock" a normal certificate to make it a CA certificate. Of course phrasing it that way wouldn't be quite so sensational (and wouldn't have accomplished the researcher's goal of raising awareness to the weakness of MD5), so now we have mass misperception, which has become reality since anything that is published is automatically true.

I'm not saying it's bad that people are shying aware from MD5, I just like to be accurate.

In any case, it has spawned some healthy discussions so I would say it was worthwhile.

CA cert:  http://www.smtps.net/pub/smtps-dot-net-ca-2.pem

Attachment: smime.p7s

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