diff options
Diffstat (limited to 'puppet/modules/site_openvpn')
| -rw-r--r-- | puppet/modules/site_openvpn/manifests/server_config.pp | 67 |
1 files changed, 66 insertions, 1 deletions
diff --git a/puppet/modules/site_openvpn/manifests/server_config.pp b/puppet/modules/site_openvpn/manifests/server_config.pp index 482c6ab7..6fc3a3c2 100644 --- a/puppet/modules/site_openvpn/manifests/server_config.pp +++ b/puppet/modules/site_openvpn/manifests/server_config.pp @@ -1,3 +1,57 @@ +# +# 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 = $name @@ -29,7 +83,18 @@ define site_openvpn::server_config ($port, $proto, $local, $server, $push, $mana 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', |