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}
384 \todo{cm: document DANE}
386 First, you need to generate Diffie Hellman parameters (please first take a look at the section \ref{section:PRNG}):
388 \todo{FIXME: this is a really weak setting! See also: http://postfix.1071664.n5.nabble.com/postfix-hardening-what-can-we-do-td61874.html}
389 \begin{lstlisting}[breaklines]
390 % openssl gendh -out /etc/postfix/dh_param_512.pem -2 512
391 % openssl gendh -out /etc/postfix/dh_param_1024.pem -2 1024
394 Next, we specify these DH parameters in \verb|main.cf|:
396 \begin{lstlisting}[breaklines]
397 smtpd_tls_dh512_param_file = /etc/postfix/dh_param_512.pem
398 smtpd_tls_dh1024_param_file = /etc/postfix/dh_param_1024.pem
401 \paragraph*{MX and SMTP client configuration}\mbox{}\\
403 As discussed above, because of opportunistic encryption we do not
404 restrict the list of ciphers. There's still some steps needed to
405 enable TLS, all in \verb|main.cf| \footnote{Refer to
406 \url{http://www.postfix.org/TLS_README.html} for an in-depth
409 \begin{lstlisting}[breaklines]
410 smtpd_tls_cert_file = /etc/postfix/server.pem
411 smtpd_tls_key_file = /etc/postfix/server.key
412 # use 0 for Postfix >= 2.9, and 1 for earlier versions
413 smtpd_tls_loglevel = 0
414 # enable opportunistic TLS support in the SMTP server and client
415 smtpd_tls_security_level = may
416 smtp_tls_security_level = may
417 # if you have authentication enabled, only offer it after STARTTLS
418 smtpd_tls_auth_only = yes
419 tls_ssl_options=NO_COMPRESSION
420 tls_random_source = dev:/dev/urandom
423 \paragraph*{MSA}\mbox{}\\
425 For the MSA \verb|smtpd| process, we first define the ciphers that are
426 acceptable for the ``mandatory'' security level, again in
429 \begin{lstlisting}[breaklines]
430 smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
431 smtpd_tls_mandatory_ciphers=high
432 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'
435 Then, we configure the MSA smtpd in \verb|master.cf| with two
436 additional options that are only used for this instance of smtpd:
438 \begin{lstlisting}[breaklines]
439 587 inet n - - - - smtpd
440 -o smtpd_tls_security_level=encrypt -o tls_preempt_cipherlist = yes
443 For those users who want to use ECC key exchange, it is possible to specify this via:
444 \begin{lstlisting}[breaklines]
445 smtpd_tls_eecdh_grade = ultra
448 You can check the settings with the following command:
449 \begin{lstlisting}[breaklines]
450 $ 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
451 1 SSLv3 with cipher DHE-RSA-AES256-SHA
452 23 TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384
453 60 TLSv1 with cipher ECDHE-RSA-AES256-SHA
454 270 TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384
455 335 TLSv1 with cipher DHE-RSA-AES256-SHA
458 \paragraph*{Limitations}\mbox{}\\
460 tls\_ssl\_options is supported from Postfix 2.11 onwards. You can
461 leave the statement in the configuration for older versions, it will
464 tls\_preempt\_cipherlist is supported from Postfix 2.8 onwards. Again,
465 you can leave the statement in for older versions.
467 \subsubsection{Exim (based on 4.82)}
469 It is highly recommended to read
471 \url{http://exim.org/exim-html-current/doc/html/spec_html/ch-encrypted_smtp_connections_using_tlsssl.html}
475 \paragraph*{MSA mode (submission)}\mbox{}\\
477 In the main config section of Exim add:
479 \begin{lstlisting}[breaklines]
480 tls_certificate = ..../cert.pem
481 tls_privatekey = ..../cert.key
483 don't forget to add intermediate certificates to the .pem file if needed.\\
485 Tell Exim to advertise STARTTLS in the EHLO answer to everyone:
486 \begin{lstlisting}[breaklines]
487 tls_advertise_hosts = *
490 If you want to support legacy SMTPS on port 465, and STARTTLS on smtp(25)/submission(587) ports set
491 \begin{lstlisting}[breaklines]
492 daemon_smtp_ports = smtp : smtps : submission
493 tls_on_connect_ports = 465
496 It is highly recommended to limit SMTP AUTH to SSL connections only. To do so add
497 \begin{lstlisting}[breaklines]
498 server_advertise_condition = ${if eq{$tls_cipher}{}{no}{yes}}
500 to every authenticator defined.\\
502 Add the following rules on top of your acl\_smtp\_mail:
503 \begin{lstlisting}[breaklines]
505 control = submission/sender_retain
507 This switches Exim to submission mode and allows addition of missing Message-ID: and Date: headers.\\
509 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.\\
510 % Exim maintainers do not recommend to change default ciphers
511 % I think we shouldn't, too
513 %\begin{lstlisting}[breaklines]
514 % tls_require_ciphers = <...recommended ciphersuite...>
517 The cipher used is written to the logfiles by default. You may want to add
518 \begin{lstlisting}[breaklines]
519 log_selector = <....whatever your log_selector already contains...> \
520 +tls_certificate_verified +tls_peerdn +tls_sni
522 to get even more TLS information logged.
525 \paragraph*{server mode (incoming)}\mbox{}\\
527 In the main config section of Exim add:
529 \begin{lstlisting}[breaklines]
530 tls_certificate = ..../cert.pem
531 tls_privatekey = ..../cert.key
533 don't forget to add intermediate certificates to the .pem file if needed.\\
535 Tell Exim to advertise STARTTLS in the EHLO answer to everyone:
536 \begin{lstlisting}[breaklines]
537 tls_advertise_hosts = *
540 Listen on smtp(25) port only
541 \begin{lstlisting}[breaklines]
542 daemon_smtp_ports = smtp
545 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.\\
546 % Exim maintainers do not recommend to change default ciphers
549 %\begin{lstlisting}[breaklines]
550 % tls_require_ciphers = <...recommended ciphersuite...>
553 If you want to request and verify client certificates from sending hosts set
554 \begin{lstlisting}[breaklines]
555 tls_verify_certificates = /etc/pki/tls/certs/ca-bundle.crt
556 tls_try_verify_hosts = *
559 tls\_try\_verify\_hosts only reports the result to your logfile. If you want to disconnect such clients you have to use
560 \begin{lstlisting}[breaklines]
564 The cipher used is written to the logfiles by default. You may want to add
565 \begin{lstlisting}[breaklines]
566 log_selector = <....whatever your log_selector already contains...> \
567 +tls_certificate_verified +tls_peerdn +tls_sni
569 to get even more TLS information logged.
571 \paragraph*{client mode (outgoing)}\mbox{}\\
573 Exim uses opportunistic encryption in the SMTP transport by default.
575 Client mode settings have to be done in the configuration section of the smtp transport (driver = smtp).
577 If you want to use a client certificate (most server certificates can be used as client certificate, too) set
578 \begin{lstlisting}[breaklines]
579 tls_certificate = .../cert.pem
580 tls_privatekey = .../cert.key
582 This is recommended for MTA-MTA traffic.\\
584 %If you want to limit used ciphers set
585 %\begin{lstlisting}[breaklines]
586 % tls_require_ciphers = <...recommended ciphersuite...>
588 % Exim Maintainers do not recommend ciphers. We shouldn't do so, too.
589 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.
591 \paragraph*{OpenSSL}\mbox{}\\
592 Exim already disables SSLv2 by default. We recommend to add
593 \begin{lstlisting}[breaklines]
594 openssl_options = +all +no_sslv2 +no_compression +cipher_server_preference
596 to the main configuration.\\
597 Note: +all is misleading here since OpenSSL only activates the most common workarounds. But that's how SSL\_OP\_ALL is defined.\\
599 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).
600 If you want to set your own DH parameters please read the TLS documentation of exim.\\
604 \paragraph*{GnuTLS}\mbox{}\\
606 GnuTLS is different in only some respects to OpenSSL:
608 \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.
609 \item There is no option like openssl\_options
612 \paragraph*{Exim string expansion}\mbox{}\\
614 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.
616 \paragraph*{Limitations}\mbox{}\\
618 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.
619 There already is a working patch to provide support:\\
620 \url{http://bugs.exim.org/show_bug.cgi?id=1397}
623 % do we need to documment starttls in detail?
624 %\subsubsection{starttls?}
628 \begin{lstlisting}[breaklines]
630 PermitEmptyPasswords no
633 HostKey /etc/ssh/ssh_host_rsa_key
635 MACs hmac-sha2-512,hmac-sha2-256,hmac-ripemd160
636 KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1
639 % XXX: curve25519-sha256@libssh.org only available upstream(!)
640 Note: older linux systems won't support SHA2, PuTTY does not support RIPE-MD160.
645 \todo{write this subsection}
646 \subsubsection{IPSec}
648 \todo{cm: check if there are downgrade attacks for checkpoint \& co} \\
649 \todo{cm: reference the paper describing how complex IPSec is and that it can't be checked properly} \\
650 \todo{cm: change this to a table format: Variant ((A,B), (recommendations, recommendations))} \\
652 \paragraph*{Assumptions}\mbox{}\\
654 We assume the usage of IKE (v1 or v2) for this document, and ESP.
656 \paragraph*{Authentication}\mbox{}\\
658 IPSEC authentication should optimally be performed via RSA signatures,
659 with a key size of 2048 bits or more. Configuring only the trusted CA
660 that issued the peer certificate provides for additional protection
661 against fake certificates.
663 If you need to use Pre-Shared Key authentication:
666 \item Choose a \textbf{random} PSK of 20 characters or more (\todo{length, references!})
667 \item Use a \textbf{separate} PSK for any IPSEC connection
668 \item Change the PSKs regularily
671 \paragraph*{Cryptographic Suites}\mbox{}\\
673 IPSEC Cryptographic Suites are pre-defined settings for all the
674 items of a configuration; they try to provide a balanced security
675 level and make setting up VPNs easier.
677 When using any of those suites, make sure to enable ``Perfect Forward
678 Secrecy`` for Phase 2, as this is not specified in the suites.
680 \verb|Suite-B-GCM-256| \footnote{\url{http://tools.ietf.org/html/rfc6379}}
681 would be roughly equivalent to ``Configuration A``, but keep in mind
682 that it uses NIST elliptic curves for the Diffie-Hellman key exchange.
684 \verb|Suite-B-GCM-128| or
685 \verb|VPN-B| \footnote{\url{http://tools.ietf.org/html/rfc4308}} would
686 be roughly equivalent to ``Configuration B``; again,
687 \verb|Suite-B-GCM-128| uses NIST elliptic curves, \verb|VPN-B| does
690 \todo{Aaron: make an example for how to include images}
691 \todo{cm: screenshots of Checkpoint settings}
693 \paragraph*{IKE or Phase 1}\mbox{}\\
695 IKE or Phase 1 is the mutual authentication and key exchange phase.
697 Use only ``main mode``, as ``aggressive mode`` has known security
698 vulnerabilities \footnote{\url{http://ikecrack.sourceforge.net/}}.
700 Encryption Algorithm: AES or CAMELLIA
702 Hash Algorithm: SHA2-256, SHA2-384 or SHA2-512
704 DH Group: Group 14--18 (2048--8192 bit DH), or 19-21 (256--521 bit
707 Lifetime: \todo{need recommendations; 1 day seems to be common practice}
709 \todo{what about CAST?}
711 \paragraph*{ESP or Phase 2}\mbox{}\\
713 Enable ``Perfect Forward Secrecy`` with a DH Group equivalent to the
716 Encryption Algorithm: AES-GCM-16, AES-CTR, AES-CCM-16, AES-CBC, SEED
717 or CAMELLIA \todo{order of this list?}
719 Hash Algorithm: none (if using AES-GCM), HMAC-SHA-SHA256 or longer
720 \todo{what about AES-XCBC-MAC?}
722 Lifetime: \todo{need recommendations; 1--8 hours seems to be common practice}
725 \subsubsection{OpenVPN}
726 \todo{cm: please write this subsubsection}
727 \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}}
729 \paragraph{Fine tuning at installation level}
731 When installing an OpenVPN server instance, you are probably using {\it easy-rsa} tools to generate the crypto stuff needed.
732 From the directory where you will run them, you can enhance you configuration by changing the following variables in {\it Vars}
734 \begin{lstlisting}[breaklines]
738 This will enhance the security of the key exchange steps by using RSA keys with a length of 2048 bits.
739 \todo{Shouldn't we need to reduce CA and certificate lifetime? Per default 10y!!}
741 \paragraph{Server Configuration}
743 In the server configuration file, you can select the algorithm that will be used for traffic encryption.
744 Based on previous recommendation established in that document, select AES with a 256 bits key in CBC mode.
746 \begin{lstlisting}[breaklines]
747 cipher AES-256-CBC # AES
751 tls-cipher TLS-DHE-RSA-WITH-AES-256-CBC-SHA
756 \todo{Explain a little bit tls-auth and auth directives + TEST}
758 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}}
759 \begin{lstlisting}[breaklines]
769 \paragraph{Client Configuration}
771 Client and server have to use identical configuration otherwise they can't communicate.
772 The {\it cipher} directive has then to be identical in both server and client configuration.
774 \begin{lstlisting}[breaklines]
775 cipher AES-256-CBC # AES
778 \todo{what about tls-auth keys/ta.key? }.
779 \todo{what about auth sha512 ?}
782 \todo{cm: please write this subsubsection}
784 \subsubsection{Cisco IPSec}
785 \todo{write this subsubsection}
787 \subsubsection{Juniper VPN}
788 \todo{write this subsubsection. AK: ask Hannes}
790 \subsubsection{L2TP over IPSec}
791 \todo{write this subsubsection}
793 \subsubsection{Racoon}
794 \todo{write this subsubsection}
797 \subsection{PGP/ GPG - Pretty Good Privacy}
799 \todo{re-work this subsection -- this is still only a draft!!}
802 \subsection{seclayer-tcp}
803 \todo{Ramin: please write this section or ask Posch}
804 For the austrian citizen card....
807 seclayer-tcp 3495/udp # securitylayer over tcp
808 seclayer-tcp 3495/tcp # securitylayer over tcp
812 \subsection{IPMI, ILO and other lights out management solutions}
813 \todo{write this!! Recommendation. Empfehlung: nie ins Internet, nur in ein eigenes mgmt VLAN, das via VPN erreichbar ist!!
817 \todo{AK: ask Klaus. Write this section, Klaus??? }
819 \subsection{Instant Messaging Systems}
820 \subsubsection{XMPP / Jabber}
821 \todo{ts: Describe ejabberd configuration. Reference to Peter`s manifesto https://github.com/stpeter/manifesto}
826 \input{proxy_solutions}
832 %%% TeX-master: "applied-crypto-hardening"