Subject: Re: [Asrg] Consent Proposal

From: "Danny Angus" <[email-masked]>
Date: Tue, 1 Jul 2003 12:09:28 +0100

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From: Yakov Shafranovich <[email-masked]>
Date: Tue, 01 Jul 2003 17:26:02 -0400

At 12:09 PM 7/1/2003 +0100, Danny Angus wrote:

> > This raises an interesting issue for the group in general. If the current
> > spam problem is not fixed, would there be a move to proprietary
> > alternative
> > email solutions such as this one?
>
>Thats a very good question, I can see a two tier system developing with 
>trusted transport being used where it is available and much less credence 
>being given to mail arriving through the older mechanisms.
>
>I'd like to think that a trust system could be added to ESMTP as a new 
>verb and MTA's could take appropriate action, therfore as the new verb 
>spreads in use more MTA's would begin to reject mail not sent using it.
>[..]

This is similar to the system proposed by Walter Dnes a short time ago. 
HOWEVER, one specific question is what determines "trust" in a "trust system".

Yakov 

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https://www1.ietf.org/mailman/listinfo/asrg

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From: "Danny Angus" <[email-masked]>
Date: Tue, 1 Jul 2003 22:54:46 +0100

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From: Markus Stumpf <[email-masked]>
Date: Wed, 2 Jul 2003 01:57:53 +0200

On Tue, Jul 01, 2003 at 10:54:46PM +0100, Danny Angus wrote:
> We can look outside the domain of mail to find workable examples of trust,
> PGP and SSL both make provision for the inclusion of out-of-channel trust
> verification. I suppose in this situation it is whom you choose to inherit
> trust from, and ultimately your trusted root trust providers.

I don't think so.

WebSites use SSL because every newspaper told Joe User that a server
without SSL is insecure and steals your credit card number. However
there are lots of Root CAs with different pricing and different
policies and to be honest I don't trust any of them getting it right.
So the Joe Users get tricked but I don't think any of the more
technically oriented gets really trust from a SSL CERT.
Thawte for example tries to trick them even more. Go to http://www.thawte.com/
and check the "SiteSeal". You can plug an image on your website that
should tell the visitor that this is a kewl secure site. They do a lot
of technical stuff and Javascript to make it as sure as possible for
spoofing, but Joe User only sees an image and he won't even understand
the technic involved. So I copy a image over and now my site is also
real kewl save and protected and no Joe User will ever notice it's a fake.
Joe User will stop looking at the browsers security info page that gives
the REAL security information but look at yet another picture and will
be tricked into a not existing security.

For PGP they create a "web of trust".
Guess what happens if I get your public key from a keyserver. Then I
create 200 fake certificates and sign your key and after that I revoke
the signs and submit it back to the keyserver. Who do you think will
trust your key any longer?

There is no such thing as established working "trust" mechanisms in the
Internet of today (IMHO!!) They all fail miserably as early as because of
non existant working revocation spreading mechanisms. If I get a CERT
from Verisign for 2 years and they revoke it after one year, who do you
think will notice that? With their security breach some months ago
antivirus producers added the falsly issued certs to their antigenes
so that the end user has at least a very little chance to notice abuse.

	\Maex

-- 
SpaceNet AG            | Joseph-Dollinger-Bogen 14 | Fon: +49 (89) 32356-0
Research & Development |       D-80807 Muenchen    | Fax: +49 (89) 32356-299
"The security, stability and reliability of a computer system is reciprocally
 proportional to the amount of vacuity between the ears of the admin"

---

From: "Danny Angus" <[email-masked]>
Date: Wed, 2 Jul 2003 09:38:22 +0100

> However

Exactly! This is a trust mechanism, for it to work you have to trust someone. End of story.

Trust mechanisms don't work without trust.

What does work are the mechanisms which exist for propogating and revoking trust, that you don't trust anyone is a completely different issue.

d/,®	šŠX§‚X¬´+‚'~Šà†Ûi³ÿðÃ
bz×è®æj)fjåŠËb�ú?jÊà

---

From: Markus Stumpf <[email-masked]>
Date: Wed, 2 Jul 2003 18:40:54 +0200

On Wed, Jul 02, 2003 at 09:38:22AM +0100, Danny Angus wrote:
> What does work are the mechanisms which exist for propogating and
> revoking trust, that you don't trust anyone is a completely different issue.

Ok, what are the "mechanisms which exist for propogating and revoking trust"?
Newspapers? I don't know of any technically oriented ones. Or more
specifically: What do I have to do so that my browser can check whether
a SSL cert for a website has been revoked?

	\Maex

---

From: "C. Wegrzyn" <[email-masked]>
Date: Wed, 02 Jul 2003 12:46:16 -0400

I'll just tell you what I designed..your mileage can vary. Trust was 
established between two parties, out of band perhaps. Once that trust 
was established all that was required was the use of X509 certs. A proxy 
in front of the MTAs would do all the rest....

Chuck

---

From: Markus Stumpf <[email-masked]>
Date: Wed, 2 Jul 2003 19:07:13 +0200

On Tue, Jul 01, 2003 at 08:12:17PM -0400, Yakov Shafranovich wrote:
> What about a central CA issuing certificates to other CAs, controlled by 
> IANA or ICANN-type of organization?

You mean to set the cat among the pigeons ;-)
What you would need is a mechanism that creates and equal level of trust.
As soon as I get a cert from CA-1 for 5 bucks and all that is needed is
a working email address and CA-2 requires payment of 100 bucks and you
have to send in legal papers and stuff you will create different levels
of trust. That's what we have now. We have DNSBLs: some use them some
not (no trust). Some block dialin IPs some not (diffferent levels of
trust). What if in a country some of the legal documents required by
CA-2 simply don't exist? In the US (I believe) there is something
called social insurance number (or the like). Maybe in Dubai (I don't
know) such a thing does not exist and nothing similar. But this would be
required by a CA to identify e.g. a person. Would it mean people from Dubai
can't get signed keys?

And there is a social/commercial problem:
What if in our country the two biggest emails providers with a share of
say 30% don't stick to that system? What would I tell my customers?
While private customers might understand it corporate customers will
not understand why they can't talk to business partners any longer.

And: you can't add pressure, as some of the smaller ISPs will say: "as
our customer you can still receive mail from them. Leave your current
ISP and join us". Big deal :(

> There are mechanisms in place to check 
> verifications of certificates in real-time, and that can be implemented as 
> well.

Hmmm ... take e.g. Verisign. I'd guess they have issued the most certs.
What do you think would be needed as infrastructure so that every
browser accessing a SSL site can verify the cert (e.g. if revoked) in
real-time?
certs work, because the producer of the browser added the CA keys
of CAs to the browser and users depend on the producers of the browser
and these depend on the CA to "do the right thing". If a key is signed
by a "trusted" CA it's also trusted "per definitionem". We don't have
working revocation mechanisms.

To make it clear:
I'd be more than glad if those methods would exist. There are patches
for nearly all Mailservers to support SSL connections (STARTTLS) but I'd
guess the percentage of mailservers using it has a lot of 0s after the
decimal point and in front of the 1.

	\Maex

---

From: "C. Wegrzyn" <[email-masked]>
Date: Wed, 02 Jul 2003 13:13:29 -0400

If  certs were to ever become a widespread reality I would rather have 
them come from my bank - I have a relationship with them - and not from 
some other 3rd party.

Chuck Wegrzyn

---

From: Markus Stumpf <[email-masked]>
Date: Wed, 2 Jul 2003 19:23:30 +0200

> in front of the MTAs would do all the rest....

I /do/ like the idea in principle.
What do you think would be required to establish a web of trust large
enough to cover the current email infrastructure.
I know quite some mailadmins (some personally, some virtually for years)
good enough to "trust" them. We could exchange the keys and have a
small web of trust. What is the benefit? I cannot reject all emails from
mailservers I don't have a key or I won't have any customers in zero time.

Current practise is to trust everyone unless configured otherwise. I don't
see a chance for a system that works the opposite way in the near future.

What we need is a simple system that says "trust me" and that even
allows to say "don't trust me" (because I am a workstation and probably
hacked or virus infected or abused).
And IMHO the cheapest, simplest and fastest method would be to associate
TXT records along with PTR records for IP addresses that would contain:
    "MTA=yes"
or
    "MTA=no"
and an optional abuse contact in form of an URI like
    "MTA=yes;mailto:[email-masked]"
    "MTA=no;http://www.example.com/abuse/contact.html"

If no such record is available it's up to you whether you accept or not.

It wouldn't break any of the existing mechanisms like forwarding, it
wouldn't have problems with large DNS packets, it uses standard existing
methods and it's easy to deploy.
However it would be weaker than RMX or SPF or ...

	\Maex

---

From: "C. Wegrzyn" <[email-masked]>
Date: Wed, 02 Jul 2003 13:33:56 -0400

Hi Markus. I have only dealt with small groups of trusts - between 
cooperating companies.  The idea was to develop a proxy that would sit 
in front of the MTAs and handle the trust.

As for doing it on a broader scale, I don't know. Trust isn't one of 
those transitive things (A trusts B, B trusts C doesn't mean A trusts 
C). If you take a service like Yahoo email I don't know if the system 
would even scale.

Chuck Wegrzyn

---

From: Yakov Shafranovich <[email-masked]>
Date: Wed, 02 Jul 2003 16:07:15 -0400

>a SSL cert for a website has been revoked?

See RFC 2459, sections 5 and 3.3 and RFC 2560

In Internet Explorer options screen (IE6), under "Advanced", "Security", 
the first  two options listed are:

"Check for publisher's certificate revocation"
"Check for server certificate revocation"

Netscape 7 and Mozilla include an option in under "Security", "Validation" 
to use the Online Certificate Status Protocol (OCSP) to verify 
certificates. This protocol is defined in RFC 2560.

Funny enough Opera 7 has none of these options but IE does. Weird.

Yakov

---

From: "Danny Angus" <[email-masked]>
Date: Wed, 2 Jul 2003 21:48:56 +0100

Hi all,

There's been some talk about trust systems recently, I think I instigated
some of it, and I feel that a number of comments have been made which kind
of miss the point about trust. I'd like to outline my take on trust and why
I believe trust should be considered by this group.

First off trust isn't an absolute. Realistically I can only trust people I
know, and even then I could misjudge them. To rely on another person's
judgement is more risky still. It is also all wrong to think of trust as YES
or NO, there are degrees of trust, some people we'd trust with our lives,
others with our car keys, yet more with our phone numbers. We don't say YES
or NO to the phone number guys, we say "I trust you just enough not to abuse
this information"

Secondly in existing trust mechanisms it is possible, but not widely used,
for end users to make decisions about whom of trust issuers they will trust,
and accept the judgement of in assessing an unknown third party.

For example It is possible to score PGP keys according to who I trust and
why, my immediate circle get full marks, those known to them will be assumed
to have a high degree of trust worthiness, and so on. When I encouter a
third party I can make a judgement according to how many of the people I
trust, and how much I trust them, have signed the certificate.

Likewise revocation could have a detrimental affect if a close associate of
mine has revoked their trust, less effect if I don't trust the revoker.

SSL certificates can be revoked if client software actually bothers to check
revokation lists.

Now Email:

Forming a judgement about whether or not to trust, and to what extent, an
unknown sending MTA is about much more than checking a certificate.
Of course a signed certificate, signed by someone I trust, can influence my
decision, like wise I can consider RBL's and other blacklists, reverse DNS
etc, etc. I could attempt to relay mail through a suspect host myself if I'm
suspicious.

So what I propose for the basis of a trust system would be for a mechanism
by which SMTP can temporarily block a transaction in order for the recipient
to carry out checks and create a trust score for the sending MTA.

If this mechanism provides for the optional exchange of certificates these
can be included in the calculation.

My Trust system would allow mail admins to set rules and thresholds for
trust, allowing admins to raise and lower the barrier of trust which could
be crossed *automatically* by well behaved hosts. Other hosts could be
rejected out of hand or sin-binned until a more thourough check is carried
out.

I could offer my scores to my friends. Who, if they trust my judgement,
could use this to help in making their judgement.

The commercial madness which is the "installed root CA certificates" of the
browsers is idiotic, I have no reason at all to trust verisign or thawte who
are those guys?!? But if my (they are respectable!) ISP had signed a
certificate, or offered me their tust rating for a host I'd be much more
likely to trust that host a bit.

Unfortunately I'm  going away for a week so I won't be able to respond to
anyones comments (or flames!) 'till I get back.

d.

---

From: Yakov Shafranovich <[email-masked]>
Date: Wed, 02 Jul 2003 16:55:43 -0400

>and accept the judgement of in assessing an unknown third party.

The trust problem has been mentioned in one of the Internet Drafts written 
by IAB (http://www.iab.org/drafts/draft-iab-e2e-futures-02.txt):

---snip---
3.1 Lack of Trust

   Perhaps the single most important change from the Internet of 15 years 
ago is
   the lack of trust between end nodes. Because the end users in the 
Internet of
   15 years ago were few, and were largely dedicated to using the Internet 
as a
   tool for computer science research and for communicating research results,
   trust between end users (and thus between the end nodes that they use) and
   between network operators and their users was simply not an issue in 
general.
   Today, the motivations of some individuals using the Internet are not 
always
   entirely ethical, and, even if they are, the assumption that end nodes will
   always co-operate to achieve some mutually beneficial action, as implied 
by the
   end to end principle, is not always accurate. In addition, the growth in 
users
   who are either not technologically sophisticated enough or simply 
uninterested
   in maintaining their own security has required network operators to 
become more
   proactive in deploying measures to prevent naive or uninterested users from
   inadvertently or intentionally generating security problems. One of the 
most
   common examples of network elements interposing between end hosts are those
   dedicated to security: firewalls, VPN tunnel endpoints, certificate 
servers,
   etc. These intermediaries are designed to protect the network from 
unimpeded
   attack or to allow two end nodes that may have no inherent reason to 
trust each
   other to achieve some level of trust; but, at the same time, they act as
   impediments for end to end communications.

---

From: "C. Wegrzyn" <[email-masked]>
Date: Wed, 02 Jul 2003 17:01:35 -0400

Danny,

 Other than providing a means for parties to accepting "trusting" 
senders, this is exactly what I implemented. I assumed that OOB was used 
to validate the trust. I didn't use PGP but felt CA's were the better 
way to go (personal belief).

Chuck Wegrzyn