42 lines
2.6 KiB
Markdown
42 lines
2.6 KiB
Markdown
# Advanced security
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## Keep the CA root key save
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As mentioned in the [backup section](/docs/backup.md), there are good reasons to not generate the CA and/or leave it on the server. This document describes how you can generate the CA and all your certificates on a secure machine and then copy only the needed files (which never includes the CA root key obviously ;) ) to the server(s) and clients.
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Execute the following commands. Note that you might want to change the volume `$PWD` or use a data docker container for this.
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docker run --net=none --rm -t -i -v $PWD:/etc/openvpn kylemanna/openvpn ovpn_genconfig -u udp://VPN.SERVERNAME.COM
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docker run --net=none --rm -t -i -v $PWD:/etc/openvpn kylemanna/openvpn ovpn_initpki
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docker run --net=none --rm -t -i -v $PWD:/etc/openvpn kylemanna/openvpn ovpn_copy_server_files
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The [`ovpn_copy_server_files`](/bin/ovpn_copy_server_files) script puts all the needed configuration in a subdirectory which defaults to `$OPENVPN/server`. All you need to do now is to copy this directory to the server and you are good to go.
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## Crypto Hardening
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If you want to select the cyphers used by OpenVPN the following parameters of the `ovpn_genconfig` might interest you:
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-T Encrypt packets with the given cipher algorithm instead of the default one (tls-cipher).
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-C A list of allowable TLS ciphers delimited by a colon (cipher).
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-a Authenticate packets with HMAC using the given message digest algorithm (auth).
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The following options have been tested successfully:
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docker run -v $OVPN_DATA:/etc/openvpn --net=none --rm kylemanna/openvpn ovpn_genconfig -C 'AES-256-CBC' -a 'SHA384'
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Changing the `tls-cipher` option seems to be more complicated because some clients (namely NetworkManager in Debian Jessie) seem to have trouble with this. Running `openvpn` manually also did not solve the issue:
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TLS Error: TLS key negotiation failed to occur within 60 seconds (check your network connectivity)
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TLS Error: TLS handshake failed
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## EasyRSA and 4096 bit RSA Keys
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EasyRSA will generate 4096 bit RSA keys when the `-e EASYRSA_KEY_SIZE=4096` argument is added to `ovpn_initpki` and `easyrsa build-client-full` commands.
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docker run -e EASYRSA_KEY_SIZE=4096 -v $OVPN_DATA:/etc/openvpn --rm -it kylemanna/openvpn ovpn_initpki
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docker run -e EASYRSA_KEY_SIZE=4096 -v $OVPN_DATA:/etc/openvpn --rm -it kylemanna/openvpn easyrsa build-client-full CLIENTNAME nopass
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## Additional Resources
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Have a look at the [Applied-Crypto-Hardening](https://github.com/BetterCrypto/Applied-Crypto-Hardening/tree/master/src/configuration/VPNs/OpenVPN) project for more examples.
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