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#
# Cipher discussion
# ================================
#
# We want to specify explicit values for the crypto options to prevent a MiTM from forcing
# a weaker cipher. These should be set in both the server and the client ('auth' and 'cipher'
# MUST be the same on both ends or no data will get transmitted).
#
# tls-cipher DHE-RSA-AES128-SHA
#
# dkg: For the TLS control channel, we want to make sure we choose a
# key exchange mechanism that has PFS (meaning probably some form of ephemeral
# Diffie-Hellman key exchange), and that uses a standard, well-tested cipher
# (I recommend AES, and 128 bits is probably fine, since there are some known
# weaknesses in the 192- and 256-bit key schedules). That leaves us with the
# choice of public key algorithms: /usr/sbin/openvpn --show-tls | grep DHE |
# grep AES128 | grep GCM.
#
# elijah:
# I could not get any of these working:
# * openvpn --show-tls | grep GCM
# * openvpn --show-tls | grep DHE | grep AES128 | grep SHA256
# so, i went with this:
# * openvpn --show-tls | grep DHE | grep AES128 | grep -v SHA256 | grep -v GCM
# Also, i couldn't get any of the elliptical curve algorithms to work. Not sure how
# our cert generation interacts with the tls-cipher algorithms.
#
# note: in my tests, DHE-RSA-AES256-SHA is the one it negotiates if no value is set.
#
# auth SHA1
#
# dkg: For HMAC digest to authenticate packets, we just want SHA256. OpenVPN lists
# a number of “digest” with names like “RSA-SHA256”, but this are legacy and
# should be avoided.
#
# elijah: i am not so sure that the digest algo matters for 'auth' option, because
# i think an attacker would have to forge the digest in real time, which is still far from
# a possibility for SHA1. So, i am leaving the default for now (SHA1).
#
# cipher AES-128-CBC
#
# dkg: For the choice of cipher, we need to select an algorithm and a
# cipher mode. OpenVPN defaults to Blowfish, which is a fine algorithm — but
# our control channel is already relying on AES not being broken; if the
# control channel is cracked, then the key material for the tunnel is exposed,
# and the choice of algorithm is moot. So it makes more sense to me to rely on
# the same cipher here: AES128. As for the cipher mode, OFB seems cleaner to
# me, but CBC is more well-tested, and the OpenVPN man page (at least as of
# version 2.2.1) says “CBC is recommended and CFB and OFB should be considered
# advanced modes.”
#
# note: the default is BF-CBC (blowfish)
#
define site_openvpn::server_config ($port, $proto, $local, $server, $push, $management ) {
$openvpn_configname = $name
concat {
"/etc/openvpn/$openvpn_configname.conf":
owner => root,
group => root,
mode => 644,
warn => true,
require => File['/etc/openvpn'],
notify => Service['openvpn'];
}
openvpn::option {
"ca $openvpn_configname":
key => 'ca',
value => '/etc/openvpn/keys/ca.crt',
server => $openvpn_configname;
"cert $openvpn_configname":
key => 'cert',
value => '/etc/openvpn/keys/server.crt',
server => $openvpn_configname;
"key $openvpn_configname":
key => 'key',
value => '/etc/openvpn/keys/server.key',
server => $openvpn_configname;
"dh $openvpn_configname":
key => 'dh',
value => '/etc/openvpn/keys/dh.pem',
server => $openvpn_configname;
"tls-cipher $openvpn_configname":
key => 'tls-cipher',
value => 'DHE-RSA-AES128-SHA',
server => $openvpn_configname;
"auth $openvpn_configname":
key => 'auth',
value => 'SHA1',
server => $openvpn_configname;
"cipher $openvpn_configname":
key => 'cipher',
value => 'AES-128-CBC',
server => $openvpn_configname;
"dev $openvpn_configname":
key => 'dev',
value => 'tun',
server => $openvpn_configname;
"duplicate-cn $openvpn_configname":
key => 'duplicate-cn',
server => $openvpn_configname;
"keepalive $openvpn_configname":
key => 'keepalive',
value => '5 20',
server => $openvpn_configname;
"local $openvpn_configname":
key => 'local',
value => $local,
server => $openvpn_configname;
"mute $openvpn_configname":
key => 'mute',
value => '5',
server => $openvpn_configname;
"mute-replay-warnings $openvpn_configname":
key => 'mute-replay-warnings',
server => $openvpn_configname;
"management $openvpn_configname":
key => 'management',
value => $management,
server => $openvpn_configname;
"proto $openvpn_configname":
key => 'proto',
value => $proto,
server => $openvpn_configname;
"push1 $openvpn_configname":
key => 'push',
value => $push,
server => $openvpn_configname;
"push2 $openvpn_configname":
key => 'push',
value => '"redirect-gateway def1"',
server => $openvpn_configname;
"script-security $openvpn_configname":
key => 'script-security',
value => '2',
server => $openvpn_configname;
"server $openvpn_configname":
key => 'server',
value => "$server",
server => $openvpn_configname;
"status $openvpn_configname":
key => 'status',
value => '/var/run/openvpn-status 10',
server => $openvpn_configname;
"status-version $openvpn_configname":
key => 'status-version',
value => '3',
server => $openvpn_configname;
"topology $openvpn_configname":
key => 'topology',
value => 'subnet',
server => $openvpn_configname;
# no need for server-up.sh right now
#"up $openvpn_configname":
# key => 'up',
# value => '/etc/openvpn/server-up.sh',
# server => $openvpn_configname;
"verb $openvpn_configname":
key => 'verb',
value => '3',
server => $openvpn_configname;
}
}
|
