Date: Fri, 6 Mar 2015 16:36:24 -0800 From: Doug Hardie <bc979@lafn.org> To: Charles Swiger <cswiger@mac.com> Cc: FreeBSD - <freebsd-questions@freebsd.org> Subject: Re: OpenSSL Ciphers Message-ID: <031A70A3-C348-4E2A-8C30-79F85BA4B4A1@lafn.org> In-Reply-To: <DC459F71-D819-4BB9-AC1A-4E1D5EB6D4E8@mac.com> References: <5347DC2D-AD6C-41A1-AEC7-A81C51F691B3@lafn.org> <B8A83AF6-B354-46E7-A736-64959C53CD66@lafn.org> <DC459F71-D819-4BB9-AC1A-4E1D5EB6D4E8@mac.com>
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> 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.home | help
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