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no cypher overlap - TLS and QMAIL

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mopani
mopani
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Upgrading to Thunderbird 38.1+ breaks SMTP TLS with Qmail.

Timestamp: 2015-08-22 21:33:32 Error: An error occurred during a connection to mail.metatek.org:465. Cannot communicate securely with peer: no common encryption algorithm(s). (Error code: ssl_error_no_cypher_overlap)

I recently replaced the certificates per https://weakdh.org/sysadmin.html but this problem with Thunderbird started more than a week later.

I find this note at http://kb.odin.com/en/123160 : 

  Qmail MTA

  Create (or edit) the /var/qmail/control/tlsserverciphers file so it looks like:

  ALL:!ADH:!LOW:!SSLv2:!SSLv3:!EXP:+HIGH:+MEDIUM

  Note: disabling SSLv3 cipher leads to impossibility to use 465 (TLS) in Thunderbird.

I find that if I enable SSLv3 I can send with TLS on port 465 or STARTTLS on port 587. This sounds like a bug that should be fixed.

Upgrading to Thunderbird 38.1+ breaks SMTP TLS with Qmail. Timestamp: 2015-08-22 21:33:32 Error: An error occurred during a connection to mail.metatek.org:465. Cannot communicate securely with peer: no common encryption algorithm(s). (Error code: ssl_error_no_cypher_overlap) I recently replaced the certificates per https://weakdh.org/sysadmin.html but this problem with Thunderbird started more than a week later. I find this note at http://kb.odin.com/en/123160 : Qmail MTA Create (or edit) the /var/qmail/control/tlsserverciphers file so it looks like: ALL:!ADH:!LOW:!SSLv2:!SSLv3:!EXP:+HIGH:+MEDIUM Note: disabling SSLv3 cipher leads to impossibility to use 465 (TLS) in Thunderbird. I find that if I enable SSLv3 I can send with TLS on port 465 or STARTTLS on port 587. This sounds like a bug that should be fixed.

Soluzione scelta

Solution: switched server from qmail to postfix which is easier to configure and more transparent in specifying cipher suites & certificates.

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christ1
christ1
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What cipher suites does your server offer? Note, the sequence is important. This is a good example: https://www.grc.com/miscfiles/SChannel_Cipher_Suites.txt

Modificato da christ1 il

mopani
mopani Utente che ha posto la domanda
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I don't know how to tell what cipher suites the server offers for SMTP. (IMAP works fine, its just SMTP that is the problem.)

starttls.info says:

Protocol 

   Supports SSLV3.
   Supports TLSV1.
   Supports TLSV1.1.
   Supports TLSV1.2.

Key exchange 

   Key size is 2048 bits; that's good.

Cipher 

   Weakest accepted cipher: 128.
   Strongest accepted cipher: 256.

But that's not cipher suites.

mopani
mopani Utente che ha posto la domanda
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How do I find out what cipher suites Thunderbird prefers?

christ1
christ1
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I don't know how to tell what cipher suites the server offers for SMTP.

If you're the admin of the server you should be able to tell that. Google is your friend.

How do I find out what cipher suites Thunderbird prefers?

That isn't really the point. If you set up your server for the cipher suites as per the GRC information I'm certain you won't see the 'ssl_error_no_cypher_overlap' error.

mopani
mopani Utente che ha posto la domanda
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Soluzione scelta

Solution: switched server from qmail to postfix which is easier to configure and more transparent in specifying cipher suites & certificates.