Use tls-crypt instead of tls-auth

[francoism90]

On the Arch Wiki tls-crypt is used as example, you'll need to change the <tls-auth> to <tls-crypt> to get it to work.

Would it be possible to set/implement this into ovpngen?

Thanks.

[graysky2]

When I take my functional openvpn server.conf and make this substitution:

#tls-auth /etc/openvpn/server/ta.key 0 # This file is secret
tls-crypt /etc/openvpn/server/ta.key 0 # This file is secret

I receive Transport Errors from the client using an unmodified profile. If I edit the profile changing this, I get the same errors and no connection. Perhaps I do not understand how to correctly enable the tls-crypt option?

</key>
<tls-crypt>
#
# 2048 bit OpenVPN static key
#
-----END OpenVPN Static key V1-----
</tls-crypt>
...

[francoism90]

Strange, I don't have any issues, only when using tls-auth together with tls-crypt.

port 1194
proto udp
dev tun
ca ca.crt
cert server.crt
key server.key
dh dh.pem
tls-crypt ta.key
server 10.8.0.0 255.255.255.0
ifconfig-pool-persist ipp.txt
keepalive 10 120
cipher AES-256-CBC
auth SHA512
compress lz4-v2
push "compress lz4-v2"
user nobody
group nobody
persist-key
persist-tun
status openvpn-status.log
verb 3
mute 20
explicit-exit-notify 1

client.ovpn

client
dev tun
remote example.org 1194 udp
resolv-retry infinite
nobind
;user nobody
;group nobody
persist-key
persist-tun
verb 3
cipher AES-256-CBC
auth SHA512
compress lz4
remote-cert-tls server
key-direction 1
<ca>
-----BEGIN CERTIFICATE-----
-----END CERTIFICATE-----
</ca>
<cert>
-----BEGIN CERTIFICATE-----
-----END CERTIFICATE-----
</cert>
<key>
-----BEGIN PRIVATE KEY-----
-----END PRIVATE KEY-----
</key>
<tls-crypt>
#
# 2048 bit OpenVPN static key
#
-----BEGIN OpenVPN Static key V1-----

-----END OpenVPN Static key V1-----
</tls-crypt>

What kind of errors do you get?

[graysky2]

Grrr... my bad. Version 1.2.5 of the iOS app has a new behavior (bug?): when users switch profiles it deems the new one "not enabled" and defaults back to the last-used profile. One has to go through extra steps to enable them.

I can now verify the behavior. The catch is that unlike encryption, the server and client profiles must match in their usage of tls-auth or tls-crypt in my testing. I am not sure how to make this script smart to see that without forcing the user to add another token corresponding to the server.conf and use some grep/sed logic to pick it. I suppose I can create a comment instructing the user to manually edit the created foo.ovpn file after it is successfully generated.

EDIT: When Look into /usr/share/openvpn/examples/server.conf provided by openvpn 2.4.4-1, I see no mention of tls-crypt therein. My though is to leave the script as-is just adding the comment.

Thoughts?

[francoism90]

@graysky2 Good solution! If I'm not mistaken the official Android OpenVPN app doesn't support tls-crypt at the moment, although it works fine in the OpenVPN for android.

The documentation and examples should be improved. It also doesn't mention the new compression options. Maybe it will be better in the next release, on the roadmap it seems they want to do a clean-up.

Thanks for the testing. :)

PS. Maybe we should change the (default) tls-crypt in the ArchWiki back to tls-auth for now.

[graysky2]

No idea about the 'droid version. I wouldn't edit the AW article removing the option since the Linux and iOS versions support it (droid support unverified). Just add a note about that.

As I stated above, the compression options are server-side implemented; the client profile doesn't need to have anything listed.

EDIT: for illustrative purposes, my server config:

cipher AES-256-CBC
auth SHA512
tls-version-min 1.2
tls-cipher TLS-DHE-RSA-WITH-AES-256-GCM-SHA384:TLS-DHE-RSA-WITH-AES-128-GCM-SHA256:TLS-DHE-RSA-WITH-AES-256-CBC-SHA:TLS-DHE-RSA-WITH-CAMELLIA-256-CBC-SHA:TLS-DHE-RSA-WITH-AES-128-CBC-SHA:TLS-DHE-RSA-WITH-CAMELLIA-128-CBC-SHA
port 443
proto tcp
dev tun
ca /etc/openvpn/server/ca.crt
cert /etc/openvpn/server/server.crt
key /etc/openvpn/server/server.key
dh /etc/openvpn/server/dh.pem
topology subnet
server 10.8.0.0 255.255.255.0
ifconfig-pool-persist ipp.txt
# next 2 lines for for pihole
push "redirect-gateway def1 bypass-dhcp"
push "dhcp-option DNS 10.1.1.250"
keepalive 10 120
tls-crypt /etc/openvpn/server/ta.key 0
compress lz4-v2
push "compress lz4-v2"
max-clients 4
user nobody
group nobody
persist-key
persist-tun
status openvpn-status.log
verb 3

And my client config:

client
dev tun
remote my.cool.domain.com 443 tcp
resolv-retry infinite
nobind
persist-key
persist-tun
verb 3
cipher AES-256-CBC
auth SHA512
remote-cert-tls server
key-direction 1
<ca>
 ...
</ca>
<cert>
 ...
</cert>
<key>
 ...
</key>
<tls-crypt>
 ...
</tls-crypt>

[slokhorst]

ArchWiki editor here. I also ran into the problem that I couldn't connect with the Android app.

Since you seem to know more about the subject, could you maybe comment here?

[graysky2]

Done... not much help though :/

[slokhorst]

Thanks both! Also thanks @graysky2 for this very useful tool. :)

[francoism90]

@slokhorst Did you test the open-source Android app instead of the official one?

[slokhorst]

Ugh I'm so sorry! I was confused by these reports on the web, but it turns out that tls-crypt is supported in the official OpenVPN Connect Android app since earlier this year.

I had messed up my .ovpn file when changing <tls-auth> to <tls-crypt>; that's why it didn't work. I'll cleanup the stuff I added to the wiki article and try to clarify things so other people don't make the same mistake I made.

To get back to the original report: maybe it's an idea to add an optional --tls-crypt flag to ovpngen that will make the substitution. And if it's not specified it just keeps on using tls-auth?

Again sorry all for the confusion.

[kennystrawnmusic]

Pro tip here — you can also pipe the output through sed before redirecting it to avoid needing to manually edit the .ovpn file, like so:

sudo ovpngen <SNIP> | sed -e "s/tls-auth/tls-crypt/g" > some_file.ovpn