MD5-CRYPT/CRAM-MD5 vs SHA512-CRYPT/PLAIN

[Reindl Harald]

Am 06.12.2014 um 14:40 schrieb Daniel Parthey:
> Am 6. Dezember 2014 13:10:58 MEZ, schrieb Reindl Harald <h.reindl at thelounge.net>:
>>
>> Am 06.12.2014 um 06:56 schrieb Jan Wideł:
>>> If you add disable_plaintext_auth=yes ssl=required settings, then
>>> dovecot will drop authentication without STARTTLS. But damage will be
>>> done, client will send unencrypted (or in this scenario MD5 or SHA512
>>> hash) login/password
>>
>> no, damage will *not* be done
>>
>> STARTTLS happens in context of connect and *log before* any
>> authentication is tried the handshake between client/server fails
>
> If the client is misconfigured to not strictly require STARTTLS, but to allow plaintext authentication too, and some man in the middle strips the STARTTLS capability from the server capability message, then the client will probably send its password login attempt in plaintext, without even trying to establish a STARTTLS session, because the server seemed to be incapable of STARTTLS.
>
> So you might need to teach your users to enforce STARTTLS in their email client in order to mitigate MITM attacks

that's so far true but:

* if you require STARTTLS try to setup the account without TLS
   fails while "not strictly require STARTTLS" is a issue of the
   past where Thunderbird offered "TLS if available"

* so that MITM needs to happen in the timeframe where the user
   configures the account the first time not chose STARTTLS

* after the account was configured that MITM is no longer possible

MITM which strips STARTTLS is more an issue in case of opportunistic TLS 
between MTA's

frankly i still don't understand the stupidity of deprecate 465 in favor 
of STARTTLS instead use 465/993/995 in context of mail-clients which 
would "MITM strip away STARTTLS" not make possible at all

from a straight technical point of view the only *real* use-case for 
STARTTLS ist MTA-to-MTA on Port 25 which don't send credentials at all



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