On Fri, Dec 27, 2013 at 09:39:52PM +0000, Viktor Dukhovni wrote:
> On Fri, Dec 27, 2013 at 03:28:46PM -0600, Bobber wrote:
>
> > >=== TLS started w/ cipher DES-CBC3-SHA
> > >=== TLS peer subject DN="/C=US/ST=Missouri/L=Saint Louis/O=The
> > >Lawrence Group/OU=IT/OU=Terms of use at www.verisign.com/rpa
> > >(c)05/CN=mail.thelawrencegroup.com"
>
> There's your problem! This server (likely Exchange 2003) has a
> broken implementation of 3DES CBC padding (search Postfix users
> archives for my posts on the subject), and your cipher list is
> either long enough to cause it to not see RC4-SHA and RC4-MD5 or
> you've disabled RC4 (directly, or by only enabling HIGH grade
> ciphers).
>
> Exchange 2003 servers can't do better than RC4-SHA.
Confirmed, this server has the Exchange 2003 cipher-count limit
problem. When RC4-SHA and RC4-MD5 are too low on the cipher-list,
TLS breaks.
If your MTA allows you configure a custom set of cipher suites for
a given set of destinations, then configure this set of cipher
suites for mail sent to Exchange 2003 machines (cipherlist setting
for Postfix "transport", Exim "router", Sendmail "mailer", etc):
aRSA+AES128+kEECDH:aRSA+AES128+kEDH:aRSA+AES128+kRSA:RC4-SHA:@STRENGTH
This cipherlist allows for the possibility of eventual upgrades
that yield AES128 support, but otherwise falls back to RC4-SHA.
The list if matching ciphers is well short of the 64 limit. In
OpenSSL 1.0.1e it comes to:
$ openssl ciphers -v \
'aRSA+AES128+kEECDH:aRSA+AES128+kEDH:aRSA+AES128+kRSA:RC4-SHA:@STRENGTH'
ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH Au=RSA Enc=AESGCM(128) Mac=AEAD
ECDHE-RSA-AES128-SHA256 TLSv1.2 Kx=ECDH Au=RSA Enc=AES(128) Mac=SHA256
ECDHE-RSA-AES128-SHA SSLv3 Kx=ECDH Au=RSA Enc=AES(128) Mac=SHA1
DHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=DH Au=RSA Enc=AESGCM(128) Mac=AEAD
DHE-RSA-AES128-SHA256 TLSv1.2 Kx=DH Au=RSA Enc=AES(128) Mac=SHA256
DHE-RSA-AES128-SHA SSLv3 Kx=DH Au=RSA Enc=AES(128) Mac=SHA1
AES128-GCM-SHA256 TLSv1.2 Kx=RSA Au=RSA Enc=AESGCM(128) Mac=AEAD
AES128-SHA256 TLSv1.2 Kx=RSA Au=RSA Enc=AES(128) Mac=SHA256
AES128-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(128) Mac=SHA1
RC4-SHA SSLv3 Kx=RSA Au=RSA Enc=RC4(128) Mac=SHA1
--
Viktor.
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