Re: TLSv1 and SSLv3
On Sun, Feb 08, 2015 at 10:41:50PM -0700, LuKreme wrote: > >> smtpd_tls_protocols = TLSv1, !SSLv2, !SSLv3 > > > > Why exclude TLSv1.1 and TLSv1.2? See the documentation. > > The default is fine, but if you must tweak, exclude just > > "SSLv2". > > > >smtpd_tls_protocols = !SSLv2 > > > > On the submission port (587) you can be more strict. > > OK, thank you for the feedback. Some of the settings were simply leftovers > I never changed, and I thought we wanted to exclude SSLv3 now. With main.cf parameter overrides, less is more. The "we" in question is people trying to secure HTTPS (mandatory TLS) in web browsers. With opportunistic TLS in SMTP, some protection is better than none. https://tools.ietf.orf/html/rfc7435 While SSLv3 will no longer be needed in 2-5 years from now, as ancient Exchange 2003 servers are phased out, there is no need to rush out and preemptively disable it in opportunistic TLS as used in MTA to MTA SMTP. Depending on who your users correspond with, you may not lose much by disabling SSLv3, but you'll not gain anything by doing so. However, while turning of SSLv3 (if you so choose) do not disable TLSv1.1 and TLSv1.2. Recommended: smtpd_tls_protocols = !SSLv2 Mostly harmless: smtpd_tls_protocols = !SSLv2, !SSLv3 -- Viktor.
Re: TLSv1 and SSLv3
On Feb 7, 2015, at 10:51 PM, Viktor Dukhovni wrote: > On Sat, Feb 07, 2015 at 10:18:11PM -0700, LuKreme wrote: > >> # postconf -n | grep _tls_ >> smtp_tls_security_level = may >> smtpd_tls_cert_file = /etc/ssl/certs/postfix.pem > > Fine so far. > >> smtpd_tls_ciphers = high > > This is too "high" for opportunistic TLS. Anything more than > "medium" is too restrictive for opportunistic TLS on port 25. > > On the submission port (587) you can be more strict. > >> # is smtp_tls_exclude needed? >> smtpd_tls_exclude_ciphers = aNULL, DES, 3DES, MD5, DES+MD5, RC4 > > The defaults are fine. Why do you feel compelled to "tune" these? > >> smtpd_tls_loglevel = 2 > > Too verbose. Stick with "1" > >> smtpd_tls_protocols = TLSv1, !SSLv2, !SSLv3 > > Why exclude TLSv1.1 and TLSv1.2? See the documentation. > The default is fine, but if you must tweak, exclude just > "SSLv2". > >smtpd_tls_protocols = !SSLv2 > > On the submission port (587) you can be more strict. OK, thank you for the feedback. Some of the settings were simply leftovers I never changed, and I thought we wanted to exclude SSLv3 now. -- 'I warn you, dragon, the human spirit is-' They never found out what it was, or at least what he thought it was, although possibly in the dark hours of a sleepless night some of them might have remembered the subsequent events and formed a pretty good and gut-churning insight, to whit, that one of the things sometimes forgotten about the human spirit is that while it is, in the right conditions, noble and brave and wonderful, it is also, when you get right down to it, only human.
Re: TLSv1 and SSLv3
On Sat, Feb 07, 2015 at 10:18:11PM -0700, LuKreme wrote: > # postconf -n | grep _tls_ > smtp_tls_security_level = may > smtpd_tls_cert_file = /etc/ssl/certs/postfix.pem Fine so far. > smtpd_tls_ciphers = high This is too "high" for opportunistic TLS. Anything more than "medium" is too restrictive for opportunistic TLS on port 25. On the submission port (587) you can be more strict. > # is smtp_tls_exclude needed? > smtpd_tls_exclude_ciphers = aNULL, DES, 3DES, MD5, DES+MD5, RC4 The defaults are fine. Why do you feel compelled to "tune" these? > smtpd_tls_loglevel = 2 Too verbose. Stick with "1" > smtpd_tls_protocols = TLSv1, !SSLv2, !SSLv3 Why exclude TLSv1.1 and TLSv1.2? See the documentation. The default is fine, but if you must tweak, exclude just "SSLv2". smtpd_tls_protocols = !SSLv2 On the submission port (587) you can be more strict. > smtpd_tls_session_cache_database = btree:$data_directory/smtpd_sessions Mostly unnecessary with Postfix 2.10 or later which supports session tickets instead. > smtpd_tls_session_cache_timeout = 1800s No reason to reduce this from the default. > # openssl s_client -connect 127.0.0.1:993 Postfix does not do IMAP, that's Dovecot or similar. -- Viktor.
Re: TLSv1 and SSLv3
On 07 Feb 2015, at 22:28 , Peter wrote: > On 02/08/2015 06:18 PM, LuKreme wrote: >> # openssl s_client -connect 127.0.0.1:993 > > Port 993 is IMAPS which is not provided by postfix. Yes, of course. Sorry. -- Gods don't like people not doing much work. People who aren't busy all the time might start to think.
Re: TLSv1 and SSLv3
On 02/08/2015 06:18 PM, LuKreme wrote: > # openssl s_client -connect 127.0.0.1:993 Port 993 is IMAPS which is not provided by postfix. Peter
TLSv1 and SSLv3
# postconf -n | grep _tls_ smtp_tls_security_level = may smtpd_tls_cert_file = /etc/ssl/certs/postfix.pem smtpd_tls_ciphers = high # is smtp_tls_exclude needed? smtpd_tls_exclude_ciphers = aNULL, DES, 3DES, MD5, DES+MD5, RC4 smtpd_tls_key_file = /etc/ssl/private/postfix.pem smtpd_tls_loglevel = 2 smtpd_tls_protocols = TLSv1, !SSLv2, !SSLv3 smtpd_tls_security_level = may smtpd_tls_session_cache_database = btree:$data_directory/smtpd_sessions smtpd_tls_session_cache_timeout = 1800s # openssl s_client -connect 127.0.0.1:993 … stuff … New, TLSv1/SSLv3, Cipher is DHE-RSA-AES256-SHA Server public key is 1024 bit Secure Renegotiation IS supported Compression: NONE Expansion: NONE SSL-Session: Protocol : TLSv1 Cipher: DHE-RSA-AES256-SHA Session-ID: 74C111205F8DC120D0A5ABAFD1CA5BE88523F775B5DCF0D13529D685369CF2ED Session-ID-ctx: Master-Key: ED4BB02DA0BDD821E96B0EAE1A6B3BA1E5147473A637A651B8D1B72CD72470512F6842652F61A37952FEC01DF321D20F Key-Arg : None Start Time: 1423372148 Timeout : 300 (sec) Verify return code: 18 (self signed certificate) --- * OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN AUTH=LOGIN] Dovecot ready. Doesn’t "New, TLSv1,SSLv3” indicate that SSLv3 is still allowed? -- the first man to hear the voice of Om, and who gave Om his view of humans, was a shepherd and not a goatherd. They have quite different ways of looking at the world, and the whole of history might have been different. For sheep are stupid and have to be driven. But goats are intelligent and have to be led. (Small Gods)
