----- Original Message ----- > From: "Reindl Harald" <h.reindl@xxxxxxxxxxxxx> > To: security@xxxxxxxxxxxxxxxxxxxxxxx > Sent: Friday, 8 August, 2014 4:45:02 PM > Subject: Re: proposed text for crypto-policies in Packaging Guidelines > > > Am 08.08.2014 um 16:30 schrieb Eric H. Christensen: > > On Fri, Aug 08, 2014 at 04:11:51PM +0200, Reindl Harald wrote: > >> Am 08.08.2014 um 15:44 schrieb Eric H. Christensen: > >>> On Fri, Aug 08, 2014 at 03:36:51PM +0200, Reindl Harald wrote: > >>>> Am 08.08.2014 um 15:21 schrieb Nikos Mavrogiannopoulos: > >>>>> Postfix is a different kind of beast though. It does not typically use > >>>>> TLS, but uses some kind of opportunistic security that allows anonymous > >>>>> ciphersuites. So it's a bit hard to enforce anything there, as > >>>>> man-in-the-middle attacks are possible by design > >>> > >>>> and keep in mind in case of opportunistic TLS if you restrict > >>>> ciphers and the SMTP client don't support what you offer it > >>>> falls back to completly plaintext which defeats the intention > >>> > >>> Falling back to an insecure cipher only provides a false sense of > >>> security > >>> which isn't any better than plaintext. > > > >> you *can not* enforce ciphers for opportunistic TLS - period > >> because that is the nature of *opportunistic* > > > > I agree with your assessment, however, ordering the ciphers that are to be > > used can still be done > > agreed, with caution below, that is still an issue and > 64 is sadly exceeded with defaults and in future versions > of openssl that will grow (new cipher types) > > [harry@srv-rhsoft:~]$ openssl ciphers -v | wc -l > 75 > > 71: RC4-SHA SSLv3 Kx=RSA Au=RSA Enc=RC4(128) Mac=SHA1 > > http://www.ietf.org/mail-archive/web/tls/current/msg10554.html > The Windows 2003 TLS stack (still used by a non-trivial number of > Microsoft Exchange SMTP servers) only looks at the first 64 elements > of the cipherlist. If neither RC4-SHA nor RC4-MD5 are among these, Which wasn't the case since openssl 1.0.1: $ openssl ciphers -v | cat -n | grep RC4 67 ECDHE-RSA-RC4-SHA SSLv3 Kx=ECDH Au=RSA Enc=RC4(128) Mac=SHA1 68 ECDHE-ECDSA-RC4-SHA SSLv3 Kx=ECDH Au=ECDSA Enc=RC4(128) Mac=SHA1 69 ECDH-RSA-RC4-SHA SSLv3 Kx=ECDH/RSA Au=ECDH Enc=RC4(128) Mac=SHA1 70 ECDH-ECDSA-RC4-SHA SSLv3 Kx=ECDH/ECDSA Au=ECDH Enc=RC4(128) Mac=SHA1 71 RC4-SHA SSLv3 Kx=RSA Au=RSA Enc=RC4(128) Mac=SHA1 72 RC4-MD5 SSLv3 Kx=RSA Au=RSA Enc=RC4(128) Mac=MD5 73 PSK-RC4-SHA SSLv3 Kx=PSK Au=PSK Enc=RC4(128) Mac=SHA1 74 KRB5-RC4-SHA SSLv3 Kx=KRB5 Au=KRB5 Enc=RC4(128) Mac=SHA1 75 KRB5-RC4-MD5 SSLv3 Kx=KRB5 Au=KRB5 Enc=RC4(128) Mac=MD5 (and is only worse for the ALL cipherstring) maybe that means that they have been falling back to plaintext since 1.0.1 release but I'd say that admins of Win2003 have much more pressing issues than security of their SMTP connections... -- Regards, Hubert Kario Quality Engineer, QE BaseOS Security team Email: hkario@xxxxxxxxxx Web: www.cz.redhat.com Red Hat Czech s.r.o., Purkyňova 99/71, 612 45, Brno, Czech Republic -- security mailing list security@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/security
