Re: [ietf-smtp] SMTP Over TLS on Port 26 - Implicit TLS Proposal

[Mark Andrews <[e-mail]>]

> On 9 Jan 2019, at 1:19 pm, Viruthagiri Thirumavalavan <[e-mail]> wrote:
> 
> The simple answer is WE DO NOT *NEED* MTA-STS.  Additionally it can be spoofed
> without DNSSEC.  The only thing it does is reduce the number of players involved
> if you are not self hosting.
> 
> I get it. You are a fan of DNSSEC. But you should know that I'm not against DNSSEC (or even STS for that matter). If you think like that, then you have not read my proposal. 
> 
> My proposal introduces SMTPS for better security and signal the port via a prefix. But authentication steps should be given to either DNSSEC or STS.
> 
> Also note, my proposal only trying to INTRODUCE the SMTPS via port 26. It doesn't force anyone to use SMTPS.
> 
> If you use the prefix in your mx host like smtps-mx1.example.com, you are saying that your server supports both port 26 and 25. Clients should drop the connection if the certificate is invalid in either port.

Which will be defeated by a MiTM attack unless DNSSEC is used.  Strip the “smtps-“ prefixes from the responses and dummy up non “smtps-" records.

> If you use the prefix in your mx host like starttls-mx1.example.com, you are saying that your server supports only port 25. Clients should drop the connection if the STARTTLS command not found in the EHLO response or valid certificate not found.

Again it can be defeated by a MiTM attack.  Same method.

> On Wed, Jan 9, 2019 at 7:38 AM Viruthagiri Thirumavalavan <giri@dombox..org> wrote:
> Oh? In what way is it "pretty good"?  Yes, SMTPS would hide the initial 220
> message, the EHLO and the response - but there's no info in those two that
> aren't already known after the 3-packet handshake and a few DNS PTR queries
> or obtained by other means - you're going to have  a really hard time claiming
> that things like 8bitmime being advertised in the EHLO reply constitute
> sensitive info.
> 
> Not every PTR queries resolves to the correct domain.
> 
> 74.125.129.26 => jm-in-f26.1e100.net (A google IP address, but point to a different domain owned by google)
> 
> I would be ok with indirectly someone getting the info rather than directly providing it.  
> 
> 
> On Wed, Jan 9, 2019 at 7:27 AM Mark Andrews <[e-mail]> wrote:
> 
> 
> > On 9 Jan 2019, at 12:42 pm, Viruthagiri Thirumavalavan <[e-mail]> wrote:
> > 
> > You just invalidated all my arguments even though I provided sources. 
> > 
> > So let me try in a different way.
> > 
> > If you think DNSSEC is so simple and not controversial, why do we need MTA-STS?
> 
> The simple answer is WE DO NOT *NEED* MTA-STS.  Additionally it can be spoofed
> without DNSSEC.  The only thing it does is reduce the number of players involved
> if you are not self hosting.
> 
> > On Wed, Jan 9, 2019, 7:02 AM Mark Andrews <[e-mail] wrote:
> > 
> > 
> > > On 9 Jan 2019, at 11:30 am, Viruthagiri Thirumavalavan <[e-mail]> wrote:
> > > 
> > > @Mark Andrews
> > > 
> > > First, When I mentioned "The former requires a HTTPS server and the latter requires DNSSEC.", I didn't mean DNSSEC is HARD to implement. I meant DNSSEC is CONTROVERSIAL
> > > 
> > > Read some of these articles.
> > > 
> > > https://sockpuppet.org/blog/2015/01/15/against-dnssec/
> > 
> > A whole heap of half truths and poor analysis.  If that was presented as a peer reviewed article it would not be published.  You have been had if you believe that blog post.
> > 
> > > https://www.theregister.co.uk/2016/02/23/dnssec_more_problem_than_solution/
> > 
> > “Oh Dear, Big Responses, The World is Going To End!!!!!”.  This is click bait journalism.  We have standard track RFCs which provide the equivalent of TCP’s three way handshake for DNS/UDP.  This has been deployed for 4+ years now along with other measures for clients that don’t implement the RFC.  8% of the TLD servers currently implement that RFC.  It is on by default in all current implementations of BIND (both client and server side) and with the exception of a handful of (non RFC compliant) servers it causes no issues.
> > 
> > > Second, unless top domains like Google, Facebook etc. start to use DNSSEC, you are gonna see questions like this.
> > > 
> > > https://security.stackexchange.com/questions/21121/if-dnssec-is-so-useful-why-is-its-deployment-non-existent-for-top-domains
> > 
> > 28171 of 895949 zones which gave good answers from the alexa to 1M are signed based on the run I started 2018-12-23T00:00:05Z.  The EDNS compliance testing I do also reports whether the returned result is signed (ok,yes) or not (ok).
> > 
> > % awk '$13 ~ /signed=ok,yes/ {yes[$1] = 1} $13 ~ /signed=ok/ { ok[$1] = 1} END { print length ( yes ) , length ( ok ) } ' reports/alexa1m.2018-12-23T00:00:05Z
> > 28171 895949
> > %
> > 
> > > So if you wanna convince others to use DNSSEC, you should start with big brothers like Google. 
> > > 
> > > Third, Yes DNSSEC is HARD. Maybe not for you. [You seem like a person who knows your stuff]
> > 
> > No it isn’t.  In Unbound it is a checkbox where the server generates the DNSKEYs and choosing the algorithm.  Are you saying ticking a checkbox is HARD?  There TLD’s with +70% of the delegated zones signed.  You don’t get to that level with “DNSSEC is HARD”.  The only reason DNSSEC is not deployed more is COMPLACENCY and FEAR OF SOMETHING NEW.
> > 
> > Neither if these reasons == HARD.
> > 
> > > We are talking about mail servers here. Many of these users are non-tech savvy users who depends on third-party mail hosting services like G-Suite.
> > 
> > Which almost certainly are using STARTTLS today and maybe using DANE today as well on the outbound side.
> > 
> > > As an engineer you can do those stuffs easily. But a doctor can't do that. Just because he can't configure DNSSEC doesn't mean he don't deserve security 
> > 
> > And he can get DNSSEC today.  There are DNS hosting providers that will do DNSSEC.  Almost all the
> > TLDs support DNSSEC.  There are DNS hosting providers that turn DNSSEC ON BY DEFAULT.  Arguing that you can’t deploy a DNSSEC signed zone today even as a lay person doesn’t bear up to scrutiny.
> > 
> > Mark
> > -- 
> > Mark Andrews, ISC
> > 1 Seymour St., Dundas Valley, NSW 2117, Australia
> > PHONE: [phone]              INTERNET: [e-mail]
> > 
> 
> -- 
> Mark Andrews, ISC
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> PHONE: [phone]              INTERNET: [e-mail]
> 
> 
> 
> -- 
> Best Regards,
> 
> Viruthagiri Thirumavalavan
> Dombox, Inc.
> 
> 
> -- 
> Best Regards,
> 
> Viruthagiri Thirumavalavan
> Dombox, Inc.
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: [phone]              INTERNET: [e-mail]