Date: Fri, 06 Mar 2015 19:35:44 -0600 From: dweimer <dweimer@dweimer.net> To: Doug Hardie <bc979@lafn.org> Cc: FreeBSD - <freebsd-questions@freebsd.org>, owner-freebsd-questions@freebsd.org Subject: Re: OpenSSL Ciphers Message-ID: <a579dadbf9688db6e2b257f76a441cc1@dweimer.net> In-Reply-To: <031A70A3-C348-4E2A-8C30-79F85BA4B4A1@lafn.org> References: <5347DC2D-AD6C-41A1-AEC7-A81C51F691B3@lafn.org> <B8A83AF6-B354-46E7-A736-64959C53CD66@lafn.org> <DC459F71-D819-4BB9-AC1A-4E1D5EB6D4E8@mac.com> <031A70A3-C348-4E2A-8C30-79F85BA4B4A1@lafn.org>
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On 03/06/2015 6:36 pm, Doug Hardie wrote: >> On 6 March 2015, at 16:28, Charles Swiger <cswiger@mac.com> wrote: >> >> Hi-- >> >>> On Mar 6, 2015, at 3:58 PM, Doug Hardie <bc979@lafn.org> wrote: >>>> On 3 March 2015, at 23:21, Doug Hardie <bc979@lafn.org> wrote: >>>> The default list of ciphers is quite extensive and includes some >>>> that are apparently causing some potential security issues. I have >>>> a number of applications that use OpenSSL and many don’t have the >>>> code to restrict the list. Fixing all that would take quite a bit >>>> of work. However, looking into /usr/include/openssl/ssl.h I find a >>>> definition for the SSL_DEFAULT_CIPHER_LIST. The comments indicate >>>> that that list is the one used when the application doesn’t specify >>>> anything. I changed its definition to: >>>> >>>> #define SSL_DEFAULT_CIPHER_LIST >>>> "TLSv1+HIGH:!SSLv2:RC4+MEDIUM:!aNULL:!eNULL:!3DES:@STRENGTH: >>>> >>>> However, s_connect will still create a connection with the export >>>> ciphers. I tried adding !EXPORT to that list and it had no effect. >>>> Is the definition actually used by openssl or is it just there for >>>> documentation? >>> >>> Not hearing anything on this, I suspect it’s not very well >>> understood. I have started updating the various servers/clients that >>> use SSL/TLS. The one that has me completely stumped is sendmail. >>> There is a web page which provides instructions >>> "http://novosial.org/sendmail/cipherlist/index.html”. However, when >>> I follow them, I can still establish a connection and deliver mail >>> using the export ciphers. >>> >>> Has anyone successfully restricted the sendmail ciphers? >> >> You can see which ciphers openssl will support via a statement like: >> >> % openssl ciphers -v >> 'TLSv1+HIGH:RC4+MEDIUM:!aNULL:!eNULL:!3DES:@STRENGTH:!EXPORT' >> DHE-RSA-AES256-SHA SSLv3 Kx=DH Au=RSA Enc=AES(256) >> Mac=SHA1 >> DHE-DSS-AES256-SHA SSLv3 Kx=DH Au=DSS Enc=AES(256) >> Mac=SHA1 >> AES256-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(256) >> Mac=SHA1 >> DHE-RSA-AES128-SHA SSLv3 Kx=DH Au=RSA Enc=AES(128) >> Mac=SHA1 >> DHE-DSS-AES128-SHA SSLv3 Kx=DH Au=DSS Enc=AES(128) >> Mac=SHA1 >> AES128-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(128) >> Mac=SHA1 >> RC4-SHA SSLv3 Kx=RSA Au=RSA Enc=RC4(128) >> Mac=SHA1 >> RC4-MD5 SSLv3 Kx=RSA Au=RSA Enc=RC4(128) >> Mac=MD5 >> RC4-MD5 SSLv2 Kx=RSA Au=RSA Enc=RC4(128) >> Mac=MD5 >> >> ...and you can experiment with TLS negotiation results via something >> like: >> >> % openssl s_client -cipher 'AES256-SHA:AES128-SHA' -connect >> www.google.com:443 >> [ ... ] >> New, TLSv1/SSLv3, Cipher is AES128-SHA >> Server public key is 2048 bit >> Secure Renegotiation IS supported >> Compression: NONE >> Expansion: NONE >> SSL-Session: >> Protocol : TLSv1 >> Cipher : AES128-SHA >> Session-ID: [ ... ] >> >> Sendmail normally performs crypto via STARTTLS negotiation rather than >> via SMTPS; there's a CipherList option which can be defined via >> sendmail.mc / sendmail.cf. You might need to recompile sendmail with >> -D_FFR_TLS_1, which I think that novosial page mentions. > > sendmail has _FFR_TLS_1 compiled in per th tests in the web page > mentioned above. The CipherList option doesn’t seem to work. I can > connect and send mail with that in place using the EXPORT ciphers. > Doug, I have this added to my /etc/mail/{HOSTNAME}.mc file. LOCAL_CONFIG O CipherList=ALL:!aNULL:!eNULL:!LOW:!EXP:RC4+RSA:+HIGH:+MEDIUM Of course you can use other options, this has been there for a while in mine, carried over from some time a few versions back. Probably should get around to testing it to make sure it actually is still working. It doesn't take long to add it in and run a quick test. -- Thanks, Dean E. Weimer http://www.dweimer.net/
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