- dovecot - dovecot.org

Re: FREAK/Logjam, and SSL protocols to use
by Jacques Distler 27 May '15

27 May '15

> For a given computational effort, you get the most bang-for-the-buck by > choosing large parameters (and checking very carefully that they are > "safe") rather than smaller parameters (and/or checking them less > carefully) which you then regenerate. This discussion (on the OpenSSH mailing list) http://marc.info/?t=143221614200001 may be helpful to those thinking about this.

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Re: FREAK/Logjam, and SSL protocols to use
by Jacques Distler 27 May '15

27 May '15

>But when you write NOT to regenerate, are you saying that using larger primes makes regenerating unnecessary, or are you telling us that it's somehow harmful? For a given computational effort, you get the most bang-for-the-buck by choosing large parameters (and checking very carefully that they are "safe") rather than smaller parameters (and/or checking them less carefully) which you then regenerate. Every time you regenerate, there's a small (but finite) probability that the new parameters are actually unsafe. You'd do better using those CPU cycles to improve the proof that your original set of parameters was safe (admittedly, no one actually does this), rather than generating a new set. Remember, the DH parameters (p,g) are NOT secret; they are transmitted in the clear everytime. As long as you're using Ephemeral Diffie-Hellman (choosing new exponents, a and b, for each session) with large safe DH parameters, it's hard to think of a threat model where you improve the security AT ALL by regenerating the DH parameters.

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Re: FREAK/Logjam, and SSL protocols to use
by Jacques Distler 27 May '15

27 May '15

>It is not at this point emphasized anywhere, including on weakdh.org, that it is actually of high importance to regenerate your DH parameters frequently. That's not really correct. If you're using a prime of length at least 2048 bits, then the corresponding discrete-log problem is well-beyond the pre-computation ability of the NSA (or anyone else). It is computationally intensive to generate such large primes, p (and corresponding base parameter, g). You need to ensure that p is actually prime (the costly step [1]) and that g is primitive. Which is why most implementations have used shorter (<= 1024 bit) primes. Using shorter primes, and regenerating DH parameters at regular intervals, is only a linear-time improvement. By contrast, generating longer DH parameters (without bothering to regenerate) is an EXPONENTIAL improvement in security. So the best setting is to set ssl_dh_parameters_length as large as feasible ([2] recommends 2048 bits), and NOT to regenerate. [1] http://en.wikipedia.org/wiki/Miller%E2%80%93Rabin_primality_test [2] https://weakdh.org/sysadmin.html

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FREAK/Logjam, and SSL protocols to use
by Ron Leach 27 May '15

27 May '15

List, good afternoon, I was reading up on a TLS Diffie Hellman protocol weakness described here https://weakdh.org/sysadmin.html which is similar to the earlier FREAK attack, and can result in downgrade of cipher suites. Part of the solution workaround that the researchers describe for Dovecot here https://weakdh.org/sysadmin.html includes altering DH parameters length to 2048, and re-specifying the allowable cipher suites - they give their suggestion. But the researchers make no comment on the allowable protocols that, in Dovecot, are controlled in 10-ssl.conf in the stanza headed # SSL protocols to use #ssl_protocols = !SSLv2 I couldn't find any advice on up-to-date SSL/TLS protocol settings in the Dovecot wiki, either (I looked in http://wiki2.dovecot.org/SSL/DovecotConfiguration ). At the moment our installation is using only the default settings for allowed protocols; I'm not sure what those defaults might be, but our 10-ssl.conf may only be disallowing SSLv2, if the 'example' entry is the default. We're running 2.2.15, and are due to upgrade to 2.2.18 shortly; quite possibly the defaults differ in a more recent release. What SSL protocols do folk on the list recommend should be allowed in Dovecot these days? (Actually, I mean which protocols really 'must' be disallowed?) regards, Ron

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/etc/ssl/certs/dovecot.pem erased by OpenSuse's update mechanism
by Wolfgang Gross 27 May '15

27 May '15

Hi, this is not a genuine Dovecot bug, more a nuisance. It applies to OpenSuse 13.2 but maybe also to other Linux's. The standard installation of Dovecot (especially 10-ssl.conf) places the certificate dovecot.pem in /etc/ssl/certs. Sometimes during updates does OpenSuse renew all certificates in /etc/ssl/certs and erases dovecot.pem. This blocks further access to the mailbox. I found a similar report here: https://bbs.archlinux.de/viewtopic.php?id=27288 Workaround: Move dovecot.pem to another directory and change 10-ssl.conf accordingly. Regards Wolfgang Gross -- Dr. W. Gross Sektion Chirurgische Forschung Klinik für Allgemein-, Viszeral- und Transplantationschirurgie Universitätsklinikum Heidelberg Im Neuenheimer Feld 365, D-69120 Heidelberg, Germany Tel. ++49 (0)6221/566392, Fax: ++49 (0)6221/566402 WGross(a)uni-hd.de

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Can email be shared between POP3 and shell account access?
by Steve Matzura 26 May '15

26 May '15

I needed to receive a message to admin(a)mydomain.com. I waited and waited for it, but it never showed up in the admin mailbox on the mydomain.com machine. So I looked for the admin account in /etc/dovecot.passwd, and there it was, plain-text password and all! I set up a retrieval system for the admin POP3 account and got all the messages I was waiting for, not to mention about 20 that I wasn't, which were obviously old and discardable. This got me to thinking, is it possible to have an account accessible not just via POP3 from the ouside, but through mail/mailx on the inside, and if so, how is that set up?

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sieve: extract first chars of body in sieve script
by Ingo Thierack 26 May '15

26 May '15

Hello, is it possible to extract the first x chars of the body of an message to forward it, or the complete body inside an sieve script. I want to forward specific mails via telegram-messenger. No Problem to extract the "from" and the "subject". if header :matches "Subject" "*" { set "subject" "${1}"; } if header :matches "from" "*" { set "from" "${1}"; } pipe :copy :try "notify.sh" [ "(${from})# ${subject}" ]; But is it also possible for the body? If I can only pass the complete body, I can cut out the first x chars inside the notify-script. Can't find any hint for that. Regards Ingo

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Segfault on "doveadm sync -u <an-specific-user> tcp:<other-node-ip>:port"
by Listas＠Adminlinux 26 May '15

26 May '15

Hi! When I run "doveadm sync -u <an-specific-user> tcp:192.168.0.2:12345", I get this error: http://pastebin.com/NxyyNGJk Only to one specific user... I've tried to repair with "doveadm force-resync", unsuccessfully. Is this known? Ubuntu14.04 + Dovecot-2.2.15. My doveconf -n: http://pastebin.com/25sURwJL Thanks! -- Thiago Henrique

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Typo in systemd commit HG 8dc79a437858
by Thomas Leuxner 25 May '15

25 May '15

The apostrophes need to be removed from the LimitCORE example, otherwise the parameter will not be recognized: $ cat /etc/systemd/system/dovecot.service.d/service.conf [Service] #Environment='OPTIONS=-p' #LimitCORE=8192 LimitCORE=infinity

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timeout for POP3 query.
by Christian Eichert 25 May '15

25 May '15

Is there a way to timeout POP3 query if they come to often? More precise I want to know if there is a setting in dovecot that makes it ignore pop3 requests from a certain user if they come more often then a certain amount of time. I am looking for a setting in dovecot, not a firewall solution. I would like dovecot to answer something like "requests come to often, please come back later." regards christian

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