confused with ssl settings and some error - need help

[Aki Tuomi]

> On April 27, 2017 at 10:55 AM Poliman - Serwis <serwis at poliman.pl> wrote:
> 
> 
> Thank You for answers. But:
> 1. How should be properly configured ssl_cipher_list?

ssl_cipher_list = ALL:!kRSA:!SRP:!kDHd:!DSS:!aNULL:!eNULL:!EXPORT:!DES:!3DES:!MD5:!PSK:!RC4:!ADH:!LOW at STRENGTH

To disable non-EC DH, use:

ssl_cipher_list = ALL:!DH:!kRSA:!SRP:!kDHd:!DSS:!aNULL:!eNULL:!EXPORT:!DES:!3DES:!MD5:!PSK:!RC4:!ADH:!LOW at STRENGTH

> 2. Ok, removed !TLSv1 !TLSv1.1.
> 3. Strange thing with ssl_protocols and ssl_cipher_list, because on older
> server on Ubuntu 14.04 LTS, dovecot 2.2.9 and postfix 2.11.0 these two
> lines looks exactly this same and no errors in mail.err file and mailes
> works without any problem.
> 4. No, currently I don't use LMTP.

it is possible that postfix is not causing this error.

> 
> 2017-04-27 8:25 GMT+02:00 Aki Tuomi <aki.tuomi at dovecot.fi>:
> 
> >
> > > On April 27, 2017 at 8:12 AM Poliman - Serwis <serwis at poliman.pl> wrote:
> > >
> > >
> > > Hi,
> > > To default dovecot.conf file I added (based on found documentation):
> > > ssl = required
> > > disable_plaintext_auth = yes     #change default 'no' to 'yes'
> > > ssl_prefer_server_ciphers = yes
> > > ssl_options = no_compression
> > > ssl_dh_parameters_length = 2048
> > > ssl_cipher_list =
> > > ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:
> > ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:
> > DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+
> > AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-
> > SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-
> > RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-
> > AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-
> > RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:
> > DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:
> > AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-
> > SHA:AES256-SHA:AES:CAMELLIA:!aNULL:!eNULL:!EXPORT:!DES:!
> > RC4:!MD5:!PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-
> > CBC3-SHA:!KRB5-DES-CBC3-SHA
> > >
> >
> > This looks rather cumbersome way to define ciphers.
> >
> > > 1. Are these settings good or can be improved?
> > > 2. Is this line proper:
> > > ssl_protocols = !SSLv2 !SSLv3 !TLSv1 !TLSv1.1
> >
> > Well if you only want to support TLSv1.2, which might lead into trouble.
> >
> > > or maybe should be:
> > > ssl_protocols = !SSLv2 !SSLv3
> > > 3. Last thing. I have below errors (they appear in loop in mail.err log
> > > file):
> > > #Apr 25 14:08:09 serwer-1 dovecot: imap-login: Error: SSL: Stacked error:
> > > error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unknown protocol
> > > #Apr 25 14:08:09 serwer-1 dovecot: imap-login: Error: SSL: Stacked error:
> > > error:1408A10B:SSL routines:ssl3_get_client_hello:wrong version number
> > > #Apr 25 14:08:51 serwer-1 dovecot: imap-login: Error: SSL: Stacked error:
> > > error:1408F119:SSL routines:SSL3_GET_RECORD:decryption failed or bad
> > record
> > > mac
> > > #Apr 25 14:08:51 serwer-1 dovecot: imap-login: Error: SSL: Stacked error:
> > > error:1408A0C1:SSL routines:ssl3_get_client_hello:no shared cipher
> >
> > This means your client did not support your enabled ciphers.
> >
> > >
> > > When I setup in postfix main.cf file (other lines default):
> > > tls_ssl_options = no_ticket, no_compression
> > > tls_preempt_cipherlist = yes
> > > smtpd_sasl_security_options=noanonymous,noplaintext
> > > smtpd_sasl_tls_security_options=noanonymous,noplaintext
> > > smtpd_tls_mandatory_ciphers = high
> > > smtpd_tls_dh1024_param_file = /etc/postfix/dh2048.pem
> > > #instead of below I tried smtpd_tls_mandatory_exclude_ciphers but I
> > don't
> > > know what should be setup
> > > smtpd_tls_exclude_ciphers = aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK,
> > > aECDH, EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CBC3-SHA,
> > ECDHE-RSA-DES-CBC3-SHA,
> > > DES-CBC3-SHA, RC4-MD5, RC4-SHA, ECDHE-RSA-RC4-SHA
> > > smtp_tls_exclude_ciphers = aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK,
> > aECDH,
> > > EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CBC3-SHA, ECDHE-RSA-DES-CBC3-SHA,
> > > DES-CBC3-SHA, RC4-MD5, RC4-SHA, ECDHE-RSA-RC4-SHA
> > >
> > > Is between dovecot and postfix some communication using above ciphers or
> > > something that generate that errors in log or maybe some public client
> > try
> > > connect and can't establish connection?
> > >
> >
> > If you are using LMTP, then some of those settings will cause changes in
> > how LMTP works as well.
> >
> >
> > > Server with Ubuntu 16.04 LTS, postfix 3.1 and dovecot 2.2.22 and openssl
> > > 1.0.2k.
> > > --
> > >
> > > *Pozdrawiam / Best Regards*
> > > *Piotr Bracha*
> > >
> > >
> > >
> > >
> > > *tel. 534 555 877*
> > >
> > > *serwis at poliman.pl <serwis at poliman.pl>*
> >
> > Aki
> >
> 
> 
> 
> -- 
> 
> *Pozdrawiam / Best Regards*
> *Piotr Bracha*
> 
> 
> 
> 
> *tel. 534 555 877*
> 
> *serwis at poliman.pl <serwis at poliman.pl>*