MAIL FROM timeout with ciphers=high

2 msg	2 postfix server on the same domain in differen...
3 msg	mailer-deamon sends error messages to: question
3 msg	Procmail

MAIL FROM timeout with ciphers=high
\ Martin Schmitt (Schmitt Systems) (30 Nov 2007)
. \ Victor Duchovni (30 Nov 2007)
. \ Bill Cole (30 Nov 2007)
. . \ Victor Duchovni (30 Nov 2007)
. . . \ Martin Schmitt (Schmitt Systems) (3 Dec 2007)
. . . . \ Victor Duchovni (3 Dec 2007)
. . . . . \ Martin Schmitt (Schmitt Systems) (6 Dec 2007)
. . . . . . \ Victor Duchovni (6 Dec 2007)
. . . . . . . \ Martin Schmitt (Schmitt Systems) (6 Dec 2007)
. . . . . . . . \ Victor Duchovni (6 Dec 2007)
. . . . . . . . . \ Martin Schmitt (Schmitt Systems) (6 Dec 2007)
. . . . . . . . . . \ Victor Duchovni (6 Dec 2007)
. . . . . . . . . . . \ Martin Schmitt (Schmitt Systems) (10 Dec 2007)
. . . . . . . . . . . . \ Victor Duchovni (10 Dec 2007)
. . \ Martin Schmitt (Schmitt Systems) (3 Dec 2007)

2 msg	milter, broken pipe
17 msg	How to listen on 587 as well as 25?
6 msg	reject_sender_login_mismatch doesnt work
2 msg	smtp auth
4 msg	Postfix with MYSQL compile error
8 msg	mynetworks=<empty> vs mynetworks=<defa...
3 msg	message_size_limit with ldap search parameter
2 msg	Pipe debugging
12 msg	destination_concurrency_limit not respected ?
13 msg	Virtual spam forwarding issues
2 msg	cleaning up deferred queue
2 msg	static nexthop per domain
2 msg	Simple postmap question
9 msg	Issues with Recipient_Canonical mapping
3 msg	Mail server reboot after got flood
3 msg	can't create a virtual domain

Subject:	MAIL FROM timeout with ciphers=high
Group:	Postfix-users
From:	Martin Schmitt (Schmitt Systems)
Date:	30 Nov 2007

Hello everyone!

I've been trying to enable Secure Channel TLS for a remote domain and am
at a point where my understanding of TLS and the ciphers seems to be too
meager to figure out what is going wrong.

With no entry or "encrypt" or "verify" or "secure" for example.com in
smtp_tls_policy_maps, mail goes out fine and the log looks like this:

Nov 30 07:10:05 gw postfix/smtp[28367]: setting up TLS connection to
exchange1.example.com
Nov 30 07:10:06 gw postfix/smtp[28367]: Verified:
subject_CN=exchange1.example.com, issuer=Thawte Premium Server CA
Nov 30 07:10:06 gw postfix/smtp[28367]: TLS connection established to
exchange1.example.com: TLSv1 with cipher RC4-MD5 (128/128 bits)
Nov 30 07:10:06 gw postfix/smtp[28367]: B0BA25009BA:
to=<user>, relay=exchange1.example.com[1.2.3.4]:25,
delay=0.54, delays=0.08/0/0.26/0.2, dsn=2.6.0, status=sent
(250 2.6.0 <474FB74B.7080901> Queued mail for delivery)

However as soon as I introduce my fully bullshit compliant ultra-secure
setting of "ciphers=high" in smtp_tls_policy_maps, what happens is this:

Nov 30 07:19:27 gw postfix/smtp[26097]: Verified:
subject_CN=exchange1.example.com, issuer=Thawte Premium Server CA
Nov 30 07:19:27 gw postfix/smtp[26097]: TLS connection established to
exchange1.example.com: TLSv1 with cipher DES-CBC3-SHA (168/168 bits)
Nov 30 07:19:28 gw postfix/smtp[26097]: AB24E500A16: lost connection
with exchange1.example.com[1.2.3.4] while sending MAIL FROM

This happens with "verify ciphers=high" as well as with "secure
ciphers=high" and "encrypt ciphers=high" in smtp_tls_policy_maps.
Delivery then moves on to their backup MX, which doesn't support TLS, so
the mail gets deferred.

It does not happen with "may ciphers=high", but with "may", the
"ciphers=high" setting seems to be ignored and the session uses RC4-MD5.
I didn't go over the docs intensely enough to see if this is intended,
but as this is an irrelevant use case here, I don't want to focus on it.

Judging from the logs, my local mailer is sending out Mail with
DES-CBC3-SHA using opportunistic TLS to other domains all the time, such
as this:

Nov 29 15:04:42 gw postfix/smtp[18005]: Unverified:
subject_CN=mx1.example.de, issuer=Some weird CA
Nov 29 15:04:42 gw postfix/smtp[18005]: TLS connection established to
mx1.example.de: TLSv1 with cipher DES-CBC3-SHA (168/168 bits)
Nov 29 15:04:42 gw postfix/smtp[18005]: A7E35500F1A:
to=<user>, relay=mx1.example.de[2.3.4.5]:25, delay=0.79,
delays=0.08/0/0.51/0.19, dsn=2.0.0, status=sent (250 251777254 message
accepted for delivery)

For completeness, here's an excerpt of the relevant parts in postconf:

# postconf -n | grep tls
smtp_tls_CApath = /etc/postfix/tls/cacerts.d
smtp_tls_loglevel = 1
smtp_tls_note_starttls_offer = yes
smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
smtp_tls_security_level = may
smtpd_tls_cert_file = /etc/postfix/tls/mx.mydomain-cert.20070319.pem
smtpd_tls_key_file = /etc/postfix/tls/mx.mydomain-key.20070319.pem
smtpd_tls_loglevel = 1
smtpd_tls_received_header = yes
smtpd_tls_security_level = may

The remote MX is running Exchange 2003, which seems to be a bit
selective about whom it wants to talk with. For example, I can't do
manual SMTP with openssl s_client, even with the latest OpenSSL release
that properly sends EHLO and when using RC4-MD5.

So, here are my questions:

- Is my Postfix installation to blame for the situation?
- If not (which is what I assume), are there any hints I can give the
remote admin in order to resolve the situation?
- Am I overrating the relevance of "ciphers=high" for my client's trade
secrets?

I'm really stuck here.

Thanks for your attention,

-martin

--
Martin Schmitt - Schmitt Systemberatung - http://www.scsy.de
DE 35415 Pohlheim, Gießener Str. 18
DE 65307 Bad Schwalbach, Am Bräunchesberg 9
Linux/UNIX - Internet - E-Mail Infrastructure - Antispam/Antivirus
- "What goes up, must come down. Ask any system administrator." -