Re: draft paper: "Deploying a New Hash Algorithm"
* Steven M. Bellovin: > I'd have phrased it differently than Perry did. I'd say that the > attackers are often cleverer *about security* than protocol designers, > because insecurity is their specialty. I think this misses the point. Hardly anybody attacks protocols. In fact, I think that those who design protocols easily outnumber those who attack them. What is being attacked aren't protocols, but implementations. More precisely, deployed implementations. (I'm not talking about PR attacks here, which can be powerful and costly as well; these are completely different matters.) I will receive a lot of flak for this from the "faith is a verb", sorry, "security is a process" crowd, but I'm convinced that at the moment, with the technology we have, security is primarily a deployment issue. This becomes becomes even more clear when you give up the misguided and completely unrealistic focus on prevention, which still plagues large parts of the industry, despite continuous failure of this approach. That's why I was shocked when one vocal critic of electronic voting disclosed that he'd never observed an actual electronic procedure. When he did, he suddenly realized that some of the attacks he'd been speculating about couldn't actually work in the field. (Other attacks still seemed realistic, though.) Or another example: Can you criticize the designers of the cookie protocol that the cookies are not sufficient for secure session management in web applications? Or that IPsec XAUTH doesn't prevent gateway impersonation attacks from insiders? There are limits what protocol designers can do, especially if the protocol is a universal building block. Security doesn't compose well, so getting individual protocols right simply isn't the whole story. Usually, it's even possible to deploy insecure protocols and implementations in a reasonably secure manner, and often, this isn't as costly as it sounds. > \item Your enemy is just as smart as you are. If we haven't seen > a given class of attack yet, it's because it hasn't been necessary; > simpler attacks have worked well enough. (Besides, how do you know > if you'll actually notice it?) I think it's also important to realize that new protocols or countermeasures which protect valuable assets (at least in the attackers' eyes) can result in a considerable shift in attack technology, especially on underlying protocols. In the DoS context, this effect is quite well-known. Once the end system's application and TCP/IP stack can withstand the attack, your network components or link bandwidth is attacked. Of course, this increases collateral damage, so it's common practice in a certain class of DoS targets not to protect your hosts as well as you could. I fear that a similar shift could occur at a protocol level. Take mail authentication, for example. We have various proposals to use DNS as a trusted data source. If attackers think that subverting mail authentication is a reasonable goal (which I doubt, but let's assume it for the sake of argument), then it might be feasible to begin large-scale attacks on DNS. Of course, these attacks would have enormous side effects, not just for mail delivery. You make one thing more secure, attacks shift to the underlying protocols which are historically weak, and everybody loses because an old, widely used protocol is suddenly put under significant stress. Maybe this fear is a bit far-fetched, especially in the SPF/DKIM/Sender-ID context, but I think the effect might indeed exist. In general, attackers don't follow an economic model. They don't necessarily attack the weakest link where their attacks might be the most effective, they just use what works for them. - The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]
Re: draft paper: "Deploying a New Hash Algorithm"
>From: "Steven M. Bellovin" <[EMAIL PROTECTED]> >Sent: Aug 5, 2005 12:04 PM >To: Steve Furlong <[EMAIL PROTECTED]> >Cc: cryptography@metzdowd.com .Subject: Re: draft paper: "Deploying a New Hash Algorithm" ... >I'd have phrased it differently than Perry did. I'd say >that the attackers are often cleverer *about security* than >protocol designers, because insecurity is their specialty. >Ordinary protocol desingers are good at designing those >protocols, but they haven't been trained to think about >security. Yes! I've noticed that it's really common for me to work on a project for a very short time (like an hour or two), and start noticing all kinds of security holes, including a lot of stuff with nothing to do with cryptography. I'll still be asking very basic questions of the other people on the project about how things are *supposed* to work, but be pointing out attacks they never thought of at the same time. I think this is just a different way of thinking. Attackers and security people do this all the time. Most normal people never do--it's like once they've got the rules in their heads, that's what's possible, and they don't even think about it. How many times, working on security for some system, have you pointed out an attack, only to hear some variation on "but who would think of that?" And you can see the same thing happening in discussions of homeland security and counterterrorism stuff. It's like most people look at the national guardsmen in the airport, and say "whew, I feel safer," rather than "what the heck are those guys supposed to do to stop hijacked planes crashing into buildings?" I like your starting points, but I think the real approach to thinking about this is a bit broader. It has to do with understanding the rules, and trying to ask, for each one, "and what makes me obey that rule?" or "what would happen if I didn't do such and so?" > --Steven M. Bellovin, http://www.cs.columbia.edu/~smb --John Kelsey - The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]
Re: draft paper: "Deploying a New Hash Algorithm"
In message <[EMAIL PROTECTED]>, Steve Furlong writes:
>> [Moderator's note: ... attackers are often cleverer than protocol
>> designers. ...
>
>Is that true? Or is it a combination of
>
>(a) a hundred attackers for every designer, and
>(b) vastly disparate rewards: continued employment and maybe some
>kudos for a designer or implementer, access to $1,000,000,000 of bank
>accounts for an attacker
>
I'd have phrased it differently than Perry did. I'd say that the
attackers are often cleverer *about security* than protocol designers,
because insecurity is their specialty. Ordinary protocol desingers are
good at designing those protocols, but they haven't been trained to
think about security. Here's how I put it in my talk at the IETF
plenary last night:
\ns{Patterns of Thought}
\item Serial number 1 of any new device is delivered to your enemy.
\item You hand your packets to your enemy for delivery.
\item Your enemy is just as smart as you are. If we haven't seen
a given class of attack yet, it's because it hasn't been necessary;
simpler attacks have worked well enough. (Besides, how do you know
if you'll actually notice it?)
\endns
--Steven M. Bellovin, http://www.cs.columbia.edu/~smb
-
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Re: draft paper: "Deploying a New Hash Algorithm"
> [Moderator's note: ... attackers are often cleverer than protocol > designers. ... Is that true? Or is it a combination of (a) a hundred attackers for every designer, and (b) vastly disparate rewards: continued employment and maybe some kudos for a designer or implementer, access to $1,000,000,000 of bank accounts for an attacker SRF -- There are no bad teachers, only defective children. - The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]
Re: draft paper: "Deploying a New Hash Algorithm"
Steve, At 05:34 PM 7/29/2005 -0400, Steven M. Bellovin wrote: In message <[EMAIL PROTECTED]>, Alex Alten write s: >At 08:12 AM 7/25/2005 -0400, Steven M. Bellovin wrote: >>In message <[EMAIL PROTECTED]>, Alex Alten >>write >>s: >> >Steve, >> > >> >This also seems to be in conjunction with the potential switch over from >> >RSA et al. to >> >ECC for PKI, etc. >> > >> >>Yes, Eric and I have been talking about that, and we'll add some >>discussion of that to the next version of the paper. > >Variable output is really needed too, say 16, 32, 64, 128, 256 and 512 bits. >And on the wishful side, the ability to optimize compression across >multiple CPUs. > That's completely orthogoal to what the paper is about. We're talking about how to convert to *any* new hash algorithm; we're not concerned with which is chosen. (I confess, though, that hash outputs of less than 128 bits don't strike me as cryptographically useful except for HMAC and the like.) Sorry for going off on a tangent. Actually 32 (or even 16) bits is really useful for retrofitting old insecure protocols where you don't want to alter the header size, you only need access control, and the packets only exist for less than 100 msecs. - Alex -- - Alex Alten [Moderator's note: I have to strongly disagree. 16 bits is rarely, if ever, of any use in authentication in a modern system. Even if you think something can't live long enough to be spoofed, it usually can, and as it turns out, attackers are often cleverer than protocol designers. Crypto is too brittle to play such games with it. --Perry] - The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]
Re: draft paper: "Deploying a New Hash Algorithm"
In message <[EMAIL PROTECTED]>, Alex Alten write s: >Steve, > >This also seems to be in conjunction with the potential switch over from >RSA et al. to >ECC for PKI, etc. > Yes, Eric and I have been talking about that, and we'll add some discussion of that to the next version of the paper. --Steven M. Bellovin, http://www.cs.columbia.edu/~smb - The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]
draft paper: "Deploying a New Hash Algorithm"
Eric Rescorla and I have written a paper "Deploying a New Hash Algorithm". A draft is available at http://www.cs.columbia.edu/~smb/papers/new-hash.ps and http://www.cs.columbia.edu/~smb/papers/new-hash.pdf . Here's the abstract: As a result of recent discoveries, the strength of hash functions such as MD5 and SHA-1 have been called into question. Regardless of whether or not it is necessary to move away from those now, it is clear that it will be necessary to do so in the not-too-distant future. This poses a number of challenges, especially for certificate-based protocols. We analyze S/MIME, TLS, and IPsec. All three require protocol or implementation changes. We explain the necessary changes, show how the conversion can be done, and list what measures should be taken immediately. - The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]
