2 \section{Recommendations on practical settings}
3 \label{section:PracticalSettings}
6 \subsection{Webservers}
11 \item[Tested with Version:]
13 \item[Settings:] \mbox{}
15 %-All +TLSv1.1 +TLSv1.2
16 \begin{lstlisting}[breaklines]
17 SSLProtocol All -SSLv2 -SSLv3
18 SSLHonorCipherOrder On
20 # Add six earth month HSTS header for all users...
21 Header add Strict-Transport-Security "max-age=15768000"
22 # If you want to protect all subdomains, use the following header
23 # ALL subdomains HAVE TO support https if you use this!
24 # Strict-Transport-Security: max-age=15768000 ; includeSubDomains
26 SSLCipherSuite 'EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EDH+CAMELLIA256:EECDH:EDH+aRSA:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!SRP:!DSS:!RC4:!SEED:!AES128:!CAMELLIA128:!ECDSA:AES256-SHA'
29 Note again, that any cipher suite starting with ECDHE can be omitted in case of doubt.
30 %% XXX NOTE TO SELF: remove from future automatically generated lists!
32 \item[Additional settings:]
34 You should redirect everything to httpS:// if possible. In Apache you can do this with the following setting inside of a VirtualHost environment:
36 \begin{lstlisting}[breaklines]
40 RewriteRule ^.*$ https://%{SERVER_NAME}%{REQUEST_URI} [L,R=permanent]
45 \item[Justification for special settings (if needed):]
51 See ssllabs in section \ref{section:Tools}
54 %XXXX ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:ECDH+3DES:DH+3DES:RSA+AES:RSA+3DES:!ADH:!AECDH:!MD5:!DSS
57 \subsubsection{lighttpd}
62 \item[Tested with Version:]
66 \item[Settings:] \mbox{}
69 %% Complete ssl.cipher-list with same algo than Apache
70 \todo{FIXME: this string seems to be wrongly formatted??}
72 \begin{lstlisting}[breaklines]
73 $SERVER["socket"] == "0.0.0.0:443" {
75 ssl.use-sslv2 = "disable"
76 ssl.use-sslv3 = "disable"
77 #ssl.use-compression obsolete >= 1.4.3.1
78 ssl.pemfile = "/etc/lighttpd/server.pem"
79 ssl.cipher-list = 'EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EDH+CAMELLIA256:EECDH:EDH+aRSA:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!SRP:!DSS:!RC4:!SEED:!AES128:!CAMELLIA128:!ECDSA:AES256-SHA'
80 ssl.honor-cipher-order = "enable"
81 setenv.add-response-header = ( "Strict-Transport-Security" => "max-age=31536000")
86 \item[Additional settings:]
88 As for any other webserver, you should redirect automatically http traffic toward httpS://
90 \begin{lstlisting}[breaklines]
91 $HTTP["scheme"] == "http" {
92 # capture vhost name with regex conditiona -> %0 in redirect pattern
93 # must be the most inner block to the redirect rule
94 $HTTP["host"] =~ ".*" {
95 url.redirect = (".*" => "https://%0$0")
102 \todo{add references}.
103 lighttpd httpS:// redirection: \url{http://redmine.lighttpd.net/projects/1/wiki/HowToRedirectHttpToHttps}
105 % add any further references or best practice documents here
107 \item[How to test:] See ssllabs in section \ref{section:Tools}
109 % describe here or point the admin to tools (can be a simple footnote or \ref{} to the tools section) which help the admin to test his settings.
113 \subsubsection{nginx}
116 \item[Tested with Version:]
120 \item[Settings:] \mbox{}
122 \begin{lstlisting}[breaklines]
123 ssl_prefer_server_ciphers on;
124 ssl_protocols -SSLv2 -SSLv3;
125 ssl_ciphers 'EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EDH+CAMELLIA256:EECDH:EDH+aRSA:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!SRP:!DSS:!RC4:!SEED:!AES128:!CAMELLIA128:!ECDSA:AES256-SHA';
126 add_header Strict-Transport-Security max-age=2592000;
127 add_header X-Frame-Options DENY;
130 %% XXX FIXME: do we need to specify dhparams? Parameter: ssl_dhparam = file. See: http://wiki.nginx.org/HttpSslModule#ssl_protocols
132 \item[Additional settings:]
134 If you decide to trust NIST's ECC curve recommendation, you can add the following line to nginx's configuration file to select special curves:
136 \begin{lstlisting}[breaklines]
137 ssl_ecdh_curve sect571k1;
140 You should redirect everything to httpS:// if possible. In Nginx you can do this with the following setting:
142 \begin{lstlisting}[breaklines]
143 rewrite ^(.*) https://$host$1 permanent;
147 \item[References:] \todo{add references}
149 \item[How to test:] See ssllabs in section \ref{section:Tools}
157 \subsubsection{MS IIS}
161 \todo{screenshots? registry key settings? }
165 \item[Tested with Version:] \todo{version?}
167 \item[Settings:] \mbox{}
170 When trying to avoid RC4 and CBC (BEAST-Attack) and requiring perfect
171 forward secrecy, Microsoft Internet Information Server (IIS) supports
172 ECDSA, but does not support RSA for key exchange (consider ECC suite
173 B doubts\footnote{\url{http://safecurves.cr.yp.to/rigid.html}}).
175 Since \verb|ECDHE_RSA_*| is not supported, a SSL certificate based on
176 elliptic curves needs to be used.
178 The configuration of cipher suites MS IIS will use can be configured in one
179 of the following ways:
181 \item Group Policy \footnote{\url{http://msdn.microsoft.com/en-us/library/windows/desktop/bb870930(v=vs.85).aspx}}
183 \item IIS Crypto~\footnote{\url{https://www.nartac.com/Products/IISCrypto/}}
187 Table~\ref{tab:MS_IIS_Client_Support} shows the process of turning on
188 one algorithm after another and the effect on the supported Clients
189 tested using https://www.ssllabs.com.
191 \verb|SSL 3.0|, \verb|SSL 2.0| and \verb|MD5| are turned off.
192 \verb|TLS 1.0| and \verb|TLS 2.0| are turned on.
199 Cipher Suite & Client \\
201 \verb|TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256| & only IE 10,11, OpenSSL 1.0.1e \\
202 \verb|TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256| & Chrome 30, Opera 17, Safari 6+ \\
203 \verb|TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA| & FF 10-24, IE 8+, Safari 5, Java 7\\
206 \caption{Client support}
207 \label{tab:MS_IIS_Client_Support}
210 Table~\ref{tab:MS_IIS_Client_Support} shows the algoriths from
211 strongest to weakest and why they need to be added in this order. For
212 example insiting on SHA-2 algorithms (only first two lines) would
213 eliminate all versions of Firefox, so the last line is needed to
214 support this browser, but should be placed at the bottom, so capable
215 browsers will choose the stronger SHA-2 algorithms.
217 \verb|TLS_RSA_WITH_RC4_128_SHA| or equivalent should also be added if
218 MS Terminal Server Connection is used (make sure to use this only in a
219 trusted environment). This suite will not be used for SSL, since we do
223 % \verb|TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256| ... only supported by: IE 10,11, OpenSSL 1.0.1e
224 % \verb|TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256| ... Chrome 30, Opera 17, Safari 6+
225 % \verb|TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA| ... Firefox 10-24, IE 8+, Safari 5, Java 7
228 Not supported Clients:
235 \item[Additional settings:]
237 %Here you can add additional settings
239 \item[Justification for special settings (if needed):]
241 % in case you have the need for further justifications why you chose this and that setting or if the settings do not fit into the standard Variant A or Variant B schema, please document this here
245 \todo{add references}
247 % add any further references or best practice documents here
249 \item[How to test:] See ssllabs in section \ref{section:Tools}
256 \subsection{Mail Servers}
258 This section documents the most common mail (SMTP) and IMAPs/POPs servers. Another option to secure IMAPs/POPs servers is to place them behind an stunnel server.
260 \subsubsection{Dovecot}
265 % Example: http://dovecot.org/list/dovecot/2013-October/092999.html
267 \begin{lstlisting}[breaklines]
268 ssl_cipher_list = 'EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EDH+CAMELLIA256:EECDH:EDH+aRSA:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!SRP:!DSS:!RC4:!SEED:!AES128:!CAMELLIA128:!ECDSA:AES256-SHA'
269 ssl_prefer_server_ciphers = yes
272 Dovecot 2.1: Almost as good as dovecot 2.2. Does not support ssl\_prefer\_server\_ciphers
274 \paragraph*{Limitations}\mbox{}\\
276 Dovecot currently does not support disabling TLS compression. Furthermore, DH parameters
277 greater than 1024bit aren't possible. The most recent version 2.2.7 of Dovecot implements
278 configurable DH parameter length
279 \footnote{\url{http://hg.dovecot.org/dovecot-2.2/rev/43ab5abeb8f0}}.
281 \subsubsection{cyrus-imapd (based on 2.4.17)}
283 \paragraph*{imapd.conf}\mbox{}\\
285 To activate SSL/TLS configure your certificate with
286 \begin{lstlisting}[breaklines]
287 tls_cert_file: .../cert.pem
288 tls_key_file: .../cert.key
291 Do not forget to add necessary intermediate certificates to the .pem file.\\
293 Limiting the ciphers provided may force (especially older) clients to connect without encryption at all! Sticking to the defaults is recommended.\\
295 If you still want to force strong encryption use
296 \begin{lstlisting}[breaklines]
297 tls_cipher_list: <...recommended ciphersuite...>
300 cyrus-imapd loads hardcoded 1024 bit DH parameters using get\_rfc2409\_prime\_1024() by default. If you want to load your own DH parameters add them PEM encoded to the certificate file given in tls\_cert\_file. Do not forget to re-add them after updating your certificate.
302 \paragraph*{cyrus.conf}\mbox{}\\
304 To support POP3/IMAP on ports 110/143 with STARTTLS add
305 \begin{lstlisting}[breaklines]
306 imap cmd="imapd" listen="imap" prefork=3
307 pop3 cmd="pop3d" listen="pop3" prefork=1
309 to the SERVICES section.\\
311 To support POP3S/IMAPS on ports 995/993 add
312 \begin{lstlisting}[breaklines]
313 imaps cmd="imapd -s" listen="imaps" prefork=3
314 pop3s cmd="pop3d -s" listen="pop3s" prefork=1
317 \paragraph*{Limitations}\mbox{}\\
319 cyrus-imapd currently (2.4.17, trunk) does not support elliptic curves. ECDHE will not work even if defined in your cipher list.\\
321 Currently there is no way to prefer server ciphers or to disable compression.\\
323 There is a working patch for all three features:
324 \url{https://bugzilla.cyrusimap.org/show_bug.cgi?id=3823}\\
326 There is no way to prevent unencrypted connections on the STARTTLS ports. You can prevent usage of plaintext login by setting
327 \begin{lstlisting}[breaklines]
330 in imapd.conf. But note that SASL PLAIN/LOGIN is still available!\\
335 % XXX config von Adi?
337 % ciphers = EDH+CAMELLIA256:EDH+aRSA:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!SRP:!DSS:!RC4:!SEED:-AES128:!CAMELLIA128:!ECDSA:AES256-SHA:EDH+AES128;
338 % options = CIPHER_SERVER_PREFERENCE
341 \subsubsection{SMTP in general}
343 SMTP usually uses opportunistic TLS. This means that an MTA will accept TLS connections when asked for it during handshake but will not require it. One should always support incoming opportunistic TLS and always try TLS handshake outgoing.\\
345 Furthermore a mailserver can operate in three modes:
347 \item As MSA (Mail Submission Agent) your mailserver receives mail from your clients MUAs (Mail User Agent).
348 \item As receiving MTA (Mail Transmission Agent, MX)
349 \item As sending MTA (SMTP client)
352 We recommend the following basic setup for all modes:
354 \item correctly setup MX, A and PTR RRs without using CNAMEs at all.
355 \item enable encryption (opportunistic TLS)
356 \item do not use self signed certificates
359 For SMTP client mode we additionally recommend:
361 \item the hostname used as HELO must match the PTR RR
362 \item setup a client certificate (most server certificates are client certificates as well)
363 \item either the common name or at least an alternate subject name of your certificate must match the PTR RR
364 \item do not modify the cipher suite for client mode
367 For MSA operation we recommend:
369 \item listen on submission port 587
370 \item enforce SMTP AUTH even for local networks
371 \item do not allow SMTP AUTH on unencrypted connections
372 \item optionally use the recommended cipher suites if (and only if) all your connecting MUAs support them
377 % Note that (with the exception of MSA mode), it might be better to allow any cipher suite -- since any encryption is better than no encryption when it comes to opportunistic TLS.
379 We strongly recommend to allow all cipher suites for anything but MSA
380 mode, because the alternative is plain text transmission.
382 \subsubsection{Postfix}
385 \item[Tested with Version:] \mbox{}
388 \item Postfix 2.9.6 (Debian Wheezy)
391 \item[Settings:] \mbox{}
393 First, you need to generate Diffie Hellman parameters (please first take a look at the section \ref{section:PRNG}):
395 \todo{FIXME: this is a really weak setting! See also: http://postfix.1071664.n5.nabble.com/postfix-hardening-what-can-we-do-td61874.html}
396 \begin{lstlisting}[breaklines]
397 % openssl gendh -out /etc/postfix/dh_param_512.pem -2 512
398 % openssl gendh -out /etc/postfix/dh_param_1024.pem -2 1024
401 Next, we specify these DH parameters in \verb|main.cf|:
403 \begin{lstlisting}[breaklines]
404 smtpd_tls_dh512_param_file = /etc/postfix/dh_param_512.pem
405 smtpd_tls_dh1024_param_file = /etc/postfix/dh_param_1024.pem
408 \paragraph*{MX and SMTP client configuration}\mbox{}\\
410 As discussed above, because of opportunistic encryption we do not
411 restrict the list of ciphers. There's still some steps needed to
412 enable TLS, all in \verb|main.cf|:
414 \begin{lstlisting}[breaklines]
415 smtpd_tls_cert_file = /etc/postfix/server.pem
416 smtpd_tls_key_file = /etc/postfix/server.key
417 # use 0 for Postfix >= 2.9, and 1 for earlier versions
418 smtpd_tls_loglevel = 0
419 # enable opportunistic TLS support in the SMTP server and client
420 smtpd_tls_security_level = may
421 smtp_tls_security_level = may
422 # if you have authentication enabled, only offer it after STARTTLS
423 smtpd_tls_auth_only = yes
424 tls_ssl_options=NO_COMPRESSION
425 tls_random_source = dev:/dev/urandom
428 \paragraph*{MSA}\mbox{}\\
430 For the MSA \verb|smtpd| process, we first define the ciphers that are
431 acceptable for the ``mandatory'' security level, again in
434 \begin{lstlisting}[breaklines]
435 smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
436 smtpd_tls_mandatory_ciphers=high
437 tls_high_cipherlist=EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EDH+CAMELLIA256:EECDH:EDH+aRSA:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!SRP:!DSS:!RC4:!SEED:!AES128:!CAMELLIA128:!ECDSA:AES256-SHA
440 Then, we configure the MSA smtpd in \verb|master.cf| with two
441 additional options that are only used for this instance of smtpd:
443 \begin{lstlisting}[breaklines]
444 587 inet n - - - - smtpd
445 -o smtpd_tls_security_level=encrypt -o tls_preempt_cipherlist = yes
448 For those users who want to use ECC key exchange, it is possible to specify this via:
449 \begin{lstlisting}[breaklines]
450 smtpd_tls_eecdh_grade = ultra
453 \item[Limitations:] \mbox{}
455 tls\_ssl\_options is supported from Postfix 2.11 onwards. You can
456 leave the statement in the configuration for older versions, it will
459 tls\_preempt\_cipherlist is supported from Postfix 2.8 onwards. Again,
460 you can leave the statement in for older versions.
464 Refer to \url{http://www.postfix.org/TLS_README.html} for an in-depth
467 % \item[Additional settings:]
468 % no additional settings
470 % \item[Justification for special settings (if needed):]
471 % no special settings
475 You can check the effect of the settings with the following command:
476 \begin{lstlisting}[breaklines]
477 $ zegrep "TLS connection established from.*with cipher" | /var/log/mail.log | awk '{printf("%s %s %s %s\n", $12, $13, $14, $15)}' | sort | uniq -c | sort -n
478 1 SSLv3 with cipher DHE-RSA-AES256-SHA
479 23 TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384
480 60 TLSv1 with cipher ECDHE-RSA-AES256-SHA
481 270 TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384
482 335 TLSv1 with cipher DHE-RSA-AES256-SHA
487 \subsubsection{Exim (based on 4.82)}
489 It is highly recommended to read
491 \url{http://exim.org/exim-html-current/doc/html/spec_html/ch-encrypted_smtp_connections_using_tlsssl.html}
495 \paragraph*{MSA mode (submission)}\mbox{}\\
497 In the main config section of Exim add:
499 \begin{lstlisting}[breaklines]
500 tls_certificate = ..../cert.pem
501 tls_privatekey = ..../cert.key
503 don't forget to add intermediate certificates to the .pem file if needed.\\
505 Tell Exim to advertise STARTTLS in the EHLO answer to everyone:
506 \begin{lstlisting}[breaklines]
507 tls_advertise_hosts = *
510 If you want to support legacy SMTPS on port 465, and STARTTLS on smtp(25)/submission(587) ports set
511 \begin{lstlisting}[breaklines]
512 daemon_smtp_ports = smtp : smtps : submission
513 tls_on_connect_ports = 465
516 It is highly recommended to limit SMTP AUTH to SSL connections only. To do so add
517 \begin{lstlisting}[breaklines]
518 server_advertise_condition = ${if eq{$tls_cipher}{}{no}{yes}}
520 to every authenticator defined.\\
522 Add the following rules on top of your acl\_smtp\_mail:
523 \begin{lstlisting}[breaklines]
525 control = submission/sender_retain
527 This switches Exim to submission mode and allows addition of missing Message-ID: and Date: headers.\\
529 It is not advisable to restrict the default cipher list for MSA mode if you don't know all connecting MUAs. If you still want to define one please consult the Exim documentation or ask on the exim-users mailinglist.\\
530 % Exim maintainers do not recommend to change default ciphers
531 % I think we shouldn't, too
533 %\begin{lstlisting}[breaklines]
534 % tls_require_ciphers = <...recommended ciphersuite...>
537 The cipher used is written to the logfiles by default. You may want to add
538 \begin{lstlisting}[breaklines]
539 log_selector = <....whatever your log_selector already contains...> \
540 +tls_certificate_verified +tls_peerdn +tls_sni
542 to get even more TLS information logged.
545 \paragraph*{server mode (incoming)}\mbox{}\\
547 In the main config section of Exim add:
549 \begin{lstlisting}[breaklines]
550 tls_certificate = ..../cert.pem
551 tls_privatekey = ..../cert.key
553 don't forget to add intermediate certificates to the .pem file if needed.\\
555 Tell Exim to advertise STARTTLS in the EHLO answer to everyone:
556 \begin{lstlisting}[breaklines]
557 tls_advertise_hosts = *
560 Listen on smtp(25) port only
561 \begin{lstlisting}[breaklines]
562 daemon_smtp_ports = smtp
565 It is not advisable to restrict the default cipher list for opportunistic encryption as used by SMTP. Do not use cipher lists recommended for HTTPS! If you still want to define one please consult the Exim documentation or ask on the exim-users mailinglist.\\
566 % Exim maintainers do not recommend to change default ciphers
569 %\begin{lstlisting}[breaklines]
570 % tls_require_ciphers = <...recommended ciphersuite...>
573 If you want to request and verify client certificates from sending hosts set
574 \begin{lstlisting}[breaklines]
575 tls_verify_certificates = /etc/pki/tls/certs/ca-bundle.crt
576 tls_try_verify_hosts = *
579 tls\_try\_verify\_hosts only reports the result to your logfile. If you want to disconnect such clients you have to use
580 \begin{lstlisting}[breaklines]
584 The cipher used is written to the logfiles by default. You may want to add
585 \begin{lstlisting}[breaklines]
586 log_selector = <....whatever your log_selector already contains...> \
587 +tls_certificate_verified +tls_peerdn +tls_sni
589 to get even more TLS information logged.
591 \paragraph*{client mode (outgoing)}\mbox{}\\
593 Exim uses opportunistic encryption in the SMTP transport by default.
595 Client mode settings have to be done in the configuration section of the smtp transport (driver = smtp).
597 If you want to use a client certificate (most server certificates can be used as client certificate, too) set
598 \begin{lstlisting}[breaklines]
599 tls_certificate = .../cert.pem
600 tls_privatekey = .../cert.key
602 This is recommended for MTA-MTA traffic.\\
604 %If you want to limit used ciphers set
605 %\begin{lstlisting}[breaklines]
606 % tls_require_ciphers = <...recommended ciphersuite...>
608 % Exim Maintainers do not recommend ciphers. We shouldn't do so, too.
609 Do not limit ciphers without a very good reason. In the worst case you end up without encryption at all instead of some weak encryption. Please consult the Exim documentation if you really need to define ciphers.
611 \paragraph*{OpenSSL}\mbox{}\\
612 Exim already disables SSLv2 by default. We recommend to add
613 \begin{lstlisting}[breaklines]
614 openssl_options = +all +no_sslv2 +no_compression +cipher_server_preference
616 to the main configuration.\\
617 Note: +all is misleading here since OpenSSL only activates the most common workarounds. But that's how SSL\_OP\_ALL is defined.\\
619 You do not need to set dh\_parameters. Exim with OpenSSL by default uses parameter initialization with the "2048-bit MODP Group with 224-bit Prime Order Subgroup" defined in section 2.2 of RFC 5114 (ike23).
620 If you want to set your own DH parameters please read the TLS documentation of exim.\\
624 \paragraph*{GnuTLS}\mbox{}\\
626 GnuTLS is different in only some respects to OpenSSL:
628 \item tls\_require\_ciphers needs a GnuTLS priority string instead of a cipher list. It is recommended to use the defaults by not defining this option. It highly depends on the version of GnuTLS used. Therefore it is not advisable to change the defaults.
629 \item There is no option like openssl\_options
632 \paragraph*{Exim string expansion}\mbox{}\\
634 Note that most of the options accept expansion strings. This way you can eg. set cipher lists or STARTTLS advertisment conditionally. Please follow the link to the official Exim documentation to get more information.
636 \paragraph*{Limitations}\mbox{}\\
638 Exim currently (4.82) does not support elliptic curves with OpenSSL. This means that ECDHE is not used even if defined in your cipher list.
639 There already is a working patch to provide support:\\
640 \url{http://bugs.exim.org/show_bug.cgi?id=1397}
643 % do we need to documment starttls in detail?
644 %\subsubsection{starttls?}
648 \begin{lstlisting}[breaklines]
650 PermitEmptyPasswords no
653 HostKey /etc/ssh/ssh_host_rsa_key
655 MACs hmac-sha2-512,hmac-sha2-256,hmac-ripemd160
656 KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1
659 % XXX: curve25519-sha256@libssh.org only available upstream(!)
660 Note: older linux systems won't support SHA2, PuTTY does not support RIPE-MD160.
665 \todo{write this subsection}
666 \subsubsection{IPSec}
668 \todo{cm: check if there are downgrade attacks for checkpoint \& co} \\
669 \todo{cm: reference the paper describing how complex IPSec is and that it can't be checked properly} \\
670 \todo{cm: change this to a table format: Variant ((A,B), (recommendations, recommendations))} \\
672 \paragraph*{Assumptions}\mbox{}\\
674 We assume the usage of IKE (v1 or v2) for this document, and ESP.
676 \paragraph*{Authentication}\mbox{}\\
678 IPSEC authentication should optimally be performed via RSA signatures,
679 with a key size of 2048 bits or more. Configuring only the trusted CA
680 that issued the peer certificate provides for additional protection
681 against fake certificates.
683 If you need to use Pre-Shared Key authentication:
686 \item Choose a \textbf{random} PSK of 20 characters or more (\todo{length, references!})
687 \item Use a \textbf{separate} PSK for any IPSEC connection
688 \item Change the PSKs regularily
691 \paragraph*{Cryptographic Suites}\mbox{}\\
693 IPSEC Cryptographic Suites are pre-defined settings for all the
694 items of a configuration; they try to provide a balanced security
695 level and make setting up VPNs easier.
697 When using any of those suites, make sure to enable ``Perfect Forward
698 Secrecy`` for Phase 2, as this is not specified in the suites.
700 \verb|Suite-B-GCM-256| \footnote{\url{http://tools.ietf.org/html/rfc6379}}
701 would be roughly equivalent to ``Configuration A``, but keep in mind
702 that it uses NIST elliptic curves for the Diffie-Hellman key exchange.
704 \verb|Suite-B-GCM-128| or
705 \verb|VPN-B| \footnote{\url{http://tools.ietf.org/html/rfc4308}} would
706 be roughly equivalent to ``Configuration B``; again,
707 \verb|Suite-B-GCM-128| uses NIST elliptic curves, \verb|VPN-B| does
710 \todo{Aaron: make an example for how to include images}
711 \todo{cm: screenshots of Checkpoint settings}
713 \paragraph*{IKE or Phase 1}\mbox{}\\
715 IKE or Phase 1 is the mutual authentication and key exchange phase.
717 Use only ``main mode``, as ``aggressive mode`` has known security
718 vulnerabilities \footnote{\url{http://ikecrack.sourceforge.net/}}.
720 Encryption Algorithm: AES or CAMELLIA
722 Hash Algorithm: SHA2-256, SHA2-384 or SHA2-512
724 DH Group: Group 14--18 (2048--8192 bit DH), or 19-21 (256--521 bit
727 Lifetime: \todo{need recommendations; 1 day seems to be common practice}
729 \todo{what about CAST?}
731 \paragraph*{ESP or Phase 2}\mbox{}\\
733 Enable ``Perfect Forward Secrecy`` with a DH Group equivalent to the
736 Encryption Algorithm: AES-GCM-16, AES-CTR, AES-CCM-16, AES-CBC, SEED
737 or CAMELLIA \todo{order of this list?}
739 Hash Algorithm: none (if using AES-GCM), HMAC-SHA-SHA256 or longer
740 \todo{what about AES-XCBC-MAC?}
742 Lifetime: \todo{need recommendations; 1--8 hours seems to be common practice}
745 \subsubsection{OpenVPN}
746 \todo{cm: please write this subsubsection}
747 \todo{We suppose user uses easy-rsa which is roughly used in all HOWTO\footnote{http://openvpn.net/index.php/open-source/documentation/howto.html}}
749 \paragraph{Fine tuning at installation level}
751 When installing an OpenVPN server instance, you are probably using {\it easy-rsa} tools to generate the crypto stuff needed.
752 From the directory where you will run them, you can enhance you configuration by changing the following variables in {\it Vars}
754 \begin{lstlisting}[breaklines]
758 This will enhance the security of the key exchange steps by using RSA keys with a length of 2048 bits.
759 \todo{Shouldn't we need to reduce CA and certificate lifetime? Per default 10y!!}
761 \paragraph{Server Configuration}
763 In the server configuration file, you can select the algorithm that will be used for traffic encryption.
764 Based on previous recommendation established in that document, select AES with a 256 bits key in CBC mode.
766 \begin{lstlisting}[breaklines]
767 cipher AES-256-CBC # AES
771 tls-cipher TLS-DHE-RSA-WITH-AES-256-CBC-SHA
776 \todo{Explain a little bit tls-auth and auth directives + TEST}
778 The following ciphers are avaible and recommended\footnote{You can retrieve the list of supported algorithm on your OpenVPN installation thanks to the command {\it openvpn --show-ciphers}}
779 \begin{lstlisting}[breaklines]
789 \paragraph{Client Configuration}
791 Client and server have to use identical configuration otherwise they can't communicate.
792 The {\it cipher} directive has then to be identical in both server and client configuration.
794 \begin{lstlisting}[breaklines]
795 cipher AES-256-CBC # AES
798 \todo{what about tls-auth keys/ta.key? }.
799 \todo{what about auth sha512 ?}
802 \todo{cm: please write this subsubsection}
804 \subsubsection{Cisco IPSec}
805 \todo{write this subsubsection}
807 \subsubsection{Juniper VPN}
808 \todo{write this subsubsection. AK: ask Hannes}
810 \subsubsection{L2TP over IPSec}
811 \todo{write this subsubsection}
813 \subsubsection{Racoon}
814 \todo{write this subsubsection}
817 \subsection{PGP/ GPG - Pretty Good Privacy}
819 \todo{re-work this subsection -- this is still only a draft!!}
822 \subsection{seclayer-tcp}
823 \todo{Ramin: please write this section or ask Posch}
824 For the austrian citizen card....
827 seclayer-tcp 3495/udp # securitylayer over tcp
828 seclayer-tcp 3495/tcp # securitylayer over tcp
832 \subsection{IPMI, ILO and other lights out management solutions}
833 \todo{write this!! Recommendation. Empfehlung: nie ins Internet, nur in ein eigenes mgmt VLAN, das via VPN erreichbar ist!!
837 \todo{AK: ask Klaus. Write this section, Klaus??? }
839 \subsection{Instant Messaging Systems}
840 \subsubsection{XMPP / Jabber}
841 \todo{ts: Describe ejabberd configuration. Reference to Peter`s manifesto https://github.com/stpeter/manifesto}
846 \input{proxy_solutions}
852 %%% TeX-master: "applied-crypto-hardening"