drduh/Debian-Privacy-Server-Guide drduh/Debian-Privacy-Server-Guide

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Guide to using a remote Debian server for security and privacy services

This is a guide to configuring and managing a domain and remote host with services such as VPN, obfuscated Tor bridge, and encrypted chat, using the Debian GNU/Linux operating system and other free software.

This guide is written for Google Compute Engine, but will very work with other providers, such as Linode or Amazon, or on any computer which will run GNU/Linux, such as a PC Engines APU in a closet. This guide uses configuration files from drduh/config.

Domain name

If you are not sure what a domain name is, skip this section for now.

I had decided to purchase duh.to from Tonic, a .to top level domain registrar. A 5 year registration cost $200 - a steep price, but not unreasonable for an esoteric ccTLD with many available short, memorable, three-letter domain names. Tonic.to also does not maintain a public whois database, which is a privacy advantage.

You could instead purchase a less expensive .com, .net or any available domain name from a variety of TLDs and registrars, though be aware of not all offer domain privacy, for instance the .us ccTLD.

After purchasing your domain, configure DNS settings. To use Google Cloud DNS with Tonic:

Wait for DNS records to propagate, which may take several hours. While you wait, feel free to learn more about Tonga.

Eventually, a WHOIS lookup will return the NS record of your hosting provider:

$ whois duh.to
Tonic whoisd V1.1
duh ns-cloud-c1.googledomains.com
duh ns-cloud-c2.googledomains.com

If it doesn't look right, log in to Tonic or your registrar and update DNS information accordingly.

Server setup

Download and configure the gcloud command line tool. Log in using the verification code:

$ gcloud auth login

Enable project billing and the Compute API, then create a project with any name:

$ PROJECT=$(tr -dc '[:lower:]' < /dev/urandom | fold -w20 | head -n1)

$ gcloud projects create $PROJECT

$ gcloud config set project $PROJECT

Set the INSTANCE, NETWORK, TYPE, and ZONE variables, as well as a recent IMAGE:

$ INSTANCE=$(tr -dc '[:lower:]' < /dev/urandom | fold -w10 | head -n1)

$ NETWORK=debian-privsec-net

$ TYPE=g1-small

$ ZONE=us-east1-a

$ IMAGE=$(gcloud compute images list | grep debian-10 | awk '{print $1}')

Create a new network:

$ gcloud compute networks create $NETWORK

Add a firewall rule for remote access to your public IP address:

$ gcloud compute --project=$PROJECT firewall-rules create public-ssh \
  --direction=INGRESS --priority=1000 --action=ALLOW \
  --network=$NETWORK --rules=tcp:22,tcp:2222 \
  --source-ranges=$(curl -sq https://icanhazip.com/) \
  --target-tags=allow-ssh

To update a rule:

$ gcloud compute firewall-rules update public-ssh \
   --source-ranges=$(curl -sq https://icanhazip.com/)

Create an instance:

$ gcloud compute --project=$PROJECT instances create $INSTANCE --zone=$ZONE \
  --machine-type=$TYPE --subnet=$NETWORK --network-tier=PREMIUM \
  --metadata=block-project-ssh-keys=true --can-ip-forward --maintenance-policy=MIGRATE \
  --no-service-account --no-scopes --tags=allow-ssh \
  --image=$IMAGE --image-project=debian-cloud \
  --boot-disk-size=10GB --boot-disk-type=pd-standard --boot-disk-device-name=$INSTANCE \
  --shielded-secure-boot --shielded-vtpm --shielded-integrity-monitoring \
  --reservation-affinity=none

Update domain records

Once an External IP address is assigned, you may want to configure a DNS record. To do so, go to Networking > Cloud DNS and select Create Zone to create a new DNS zone.

Create an A record for the domain by selecting Add Record Set:

Select Create.

After a short while, verify an A record is returned with the correct IPv4 address for the instance:

$ dig +short a duh.to
104.197.215.107

If it doesn't work, wait longer for records to propagate, or try specifying the registrar's name severs:

$ dig +short a duh.to @ns-cloud-c1.googledomains.com
104.197.215.107

Likewise, there should be SOA records:

$ dig +short soa duh.to
ns-cloud-c1.googledomains.com. cloud-dns-hostmaster.google.com. 1 21600 3600 1209600 300

Setup access

Use an existing YubiKey:

$ ssh-add -L
ssh-rsa AAAAB4NzaC1yc2EAAAADAQABAAACAz[...]zreOKM+HwpkHzcy9DQcVG2Nw== cardno:000605553211

Or create a new 4096-bit RSA key-pair to use for logging into the instance via SSH:

$ ssh-keygen -t rsa -b 4096 -C 'sysadm' -f ~/.ssh/duh

Where sysadm is the desired username on the instance.

Create a temporary file in metadata format:

$ (echo -n "sysadm:" ; cat ~/.ssh/duh.pub) > /tmp/ssh-public-key
sysadm:ssh-rsa AAAAB3Nza[...]

Update instance metadata:

$ gcloud compute instances add-metadata $INSTANCE --zone=$ZONE --metadata-from-file ssh-keys=/tmp/ssh-public-key

Connect

On a client, edit ~/.ssh/config to use the new key:

Host duh
  User sysadm
  HostName duh.to
  #HostName 104.197.215.107
  IdentityFile ~/.ssh/duh

The first time you connect, you will see a warning about the host authenticity:

$ ssh duh
[...]
The authenticity of host 'duh' (104.197.215.107)' can't be established.
ECDSA key fingerprint is d6:9a:...:1d:c1.
Are you sure you want to continue connecting (yes/no)? yes

See YubiKey Guide to secure SSH keys.

Apply updates

Install pending updates:

$ sudo apt update && sudo apt upgrade -y

Install any necessary software, for example:

$ sudo apt -y install zsh vim tmux dnsutils whois git gcc autoconf make lsof tcpdump htop tree apt-transport-https

Configure instance

Clone the configuration repository:

$ git clone https://github.com/drduh/config

SSH

Take a few steps to harden remote access: declare which users are allowed to log in, change the default listening port and generate a new host key.

On a local machine (not the remote host), create new RSA keys (do not use a pass-phrase - else you won't be able to connect remotely after a reboot):

$ cd /tmp

$ ssh-keygen -t rsa -b 4096 -f ssh_host_key -C '' -N ''

$ scp /tmp/ssh_host_key* duh:~

On the remote host, move the keys into place and lock down file permissions:

$ sudo mv ssh_host_key ssh_host_key.pub /etc/ssh/

$ sudo chown root:root /etc/ssh/ssh_host_key /etc/ssh/ssh_host_key.pub

$ sudo chmod 0600 /etc/ssh/ssh_host_key

Use my configuration:

$ sudo cp ~/config/sshd_config /etc/ssh/

Or customize your own.

Do not exit the current SSH session yet; first make sure you can still connect!

Restart SSH server:

$ sudo service ssh restart

On a client, edit ~/.ssh/config to make any modifications, for example by adding Port 2222:

Host duh
  User sysadm
  HostName duh.to
  IdentityFile ~/.ssh/duh
  Port 2222

Start a new SSH session. The new key fingerprint will require verification:

$ ssh duh
The authenticity of host '[104.197.215.107]:2222 ([104.197.215.107]:2222)' can't be established.
RSA key fingerprint is 19:de:..:fe:58:3a.
Are you sure you want to continue connecting (yes/no)? yes

To check the SHA256 fingerprint of the host key from the previously established session:

$ sudo ssh-keygen -E sha256 -lf /etc/ssh/ssh_host_key.pub
4096 SHA256:47DEQpj8HBSa+/TImW+6JCeuQfRkm5NMpJWZG3hSuFU no comment (RSA)

To check the MD5 fingerprint of the host key:

$ ssh-keygen -E md5 -lf /etc/ssh/ssh_host_key.pub
4096 19:de:..:fe:58:3a /etc/ssh/ssh_host_key.pub (RSA)

If the fingerprint matches the local file version, exit the original SSH session.

tmux

tmux is a terminal multiplexer. This program allows reconnecting to a working terminal session on the instance.

Use my configuration:

$ cp ~/config/tmux.conf ~/.tmux.conf

Or customize your own.

Run tmux and open a new tab with `-c or specified keyboard shortcut.

`-1, `-2, `-3 switch to windows 1, 2, 3, etc.

`-d will disconnect from tmux, saving the existing session.

When you reconnect to the instance, type tmux attach -t <session name> (or tmux a for short) to select a session to "attach" to (default name is "0"; use `-$ to rename).

Note If you're using the st terminal and receive the error open terminal failed: missing or unsuitable terminal: st-256color, copy the file st.info from the st directory to the instance and run tic st.info.

Zsh

Z shell is an interactive login shell with many features and improvements over Bourne shell.

To set the login shell for the current user to Zsh:

$ sudo chsh -s /usr/bin/zsh $USER

Use my configuration:

$ cp ~/config/zshrc .zshrc

Or customize your own.

Open a new tmux tab and run zsh or start a new ssh session to make sure the configuration is working to your liking.

Vim

Vim is an excellent open source text editor. Run vimtutor if you have not used Vim before.

Use my configuration:

$ cp ~/config/vimrc .vimrc

$ mkdir -p ~/.vim/{backup,swap,undo}

Or customize your own vimrc.

Services

Dnsmasq

Dnsmasq is a lightweight DNS and DHCP server with many useful features.

Install Dnsmasq:

$ sudo apt -y install dnsmasq

Use my configuration and blocklist(s):

$ sudo cp ~/config/dnsmasq.conf /etc/dnsmasq.conf

$ cat ~/config/domains/* | sudo tee -a /etc/dnsmasq.conf

Or customize your own.

Pick an upstream name server by uncommenting a line in /etc/dnsmasq.conf.

Optional Install a DNS blocklist (alternative method), for example:

$ curl https://raw.githubusercontent.com/StevenBlack/hosts/master/hosts | sudo tee /etc/dns-blocklist

Append any additional lists, such as social-hosts:

$ curl https://raw.githubusercontent.com/Sinfonietta/hostfiles/master/social-hosts | sudo tee --append /etc/dns-blocklist

Check the number of file entries and ensure no routable addresses were appended:

$ wc -l /etc/dns-blocklist
66290 /etc/dns-blocklist

$ grep -ve "^.*#\|^127.0.0.1\|^0.0.0.0\|^#\|^::1" /etc/dns-blocklist | sort | uniq
255.255.255.255 broadcasthost
fe80::1%lo0 localhost
ff00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

Restart the service:

$ sudo service dnsmasq restart

Check the log to make sure it is running:

$ sudo tail -F /tmp/dns
started, version 2.76 cachesize 2000
compile time options: IPv6 GNU-getopt DBus i18n IDN DHCP DHCPv6 no-Lua TFTP conntrack ipset auth DNSSEC loop-detect inotify
compile time options: IPv6 GNU-getopt DBus i18n IDN DHCP DHCPv6 no-Lua TFTP conntrack ipset auth DNSSEC loop-detect inotify
reading /etc/resolv.dnsmasq
using nameserver 169.254.169.254#53
read /etc/hosts - 6 addresses
read /etc/dns-blocklist - 63894 addresses

If it fails to start, try running it manually:

$ sudo dnsmasq -C /etc/dnsmasq.conf -d

Query locally for an A record to confirm dnsmasq is working:

$ dig +short a google.to @127.0.0.1
74.125.202.105
74.125.202.103
74.125.202.104
74.125.202.99

DNSCrypt

DNSCrypt software can be used as a server and client to encrypt DNS traffic, as well as filter and shape queries.

If you are running your own private or public recursive DNS server, adding support for the DNSCrypt protocol requires installing DNSCrypt-Wrapper, the server-side DNSCrypt proxy.

To configure a private or public DNSCrypt server, first install libsodium and libevent:

$ sudo apt -y install libsodium-dev libevent-dev

Clone the DNSCrypt-Wrapper repository, make and install the software:

$ git clone --recursive git://github.com/Cofyc/dnscrypt-wrapper.git

$ cd dnscrypt-wrapper

$ make configure

$ ./configure

$ sudo make install

See instructions Cofyc/dnscrypt-wrapper to configure or use drduh/config/scripts/dnscrypt.sh:

$ mkdir ~/dnscrypt-keys

$ cd ~/dnscrypt-keys

$ cp ~/config/scripts/dnscrypt.sh .

$ chmod +x dnscrypt.sh

$ sudo ./dnscrypt.sh

Copy the sdns:// line to a client. To use a port other than 443, use https://dnscrypt.info/stamps to update the value.

Update firewall rules to allow the new port:

$ gcloud compute firewall-rules create dnscrypt-udp-443 --network $NETWORK \
  --allow udp:443 --source-ranges $(curl -sq https://icanhazip.com/)

On a client, edit dnscrypt-proxy.toml to include the server stamp:

listen_addresses = ['127.0.0.1:40']
server_names = ['abc']
[static]
  [static.'abc']
  stamp = 'sdns://AQAAAAAAAAAAEj...ZA'

See drduh/config/dnscrypt-proxy.toml and jedisct1/dnscrypt-proxy/example-dnscrypt-proxy.toml for examples.

Start the client manually:

$ sudo ./dnscrypt-proxy

Check the logfile:

$ tail -f dnscrypt.log
[NOTICE] dnscrypt-proxy 2.0.33
[NOTICE] Network connectivity detected
[NOTICE] Firefox workaround initialized
[NOTICE] Loading the set of blocking rules from [blacklist.txt]
[NOTICE] Loading the set of forwarding rules from [forwarding-rules.txt]
[NOTICE] Loading the set of IP blocking rules from [ip-blacklist.txt]
[NOTICE] Now listening to 127.0.0.1:4200 [UDP]
[NOTICE] Now listening to 127.0.0.1:4200 [TCP]
[NOTICE] [abc] OK (DNSCrypt) - rtt: 10ms
[NOTICE] Server with the lowest initial latency: abc (rtt: 10ms)
[NOTICE] dnscrypt-proxy is ready - live servers: 1

Install the service:

$ sudo ./dnscrypt-proxy -service install

$ sudo ./dnscrypt-proxy -service start

Edit /etc/dnsmasq.conf on the client and append server=127.0.0.1#4200 to use DNSCrypt with dnsmasq.

Blacklist

DNSCrypt supports query blocking with regular expression matching.

On the client, clone the dnscrypt-proxy repository and use the included Python script to generate a list, then configure dnscrypt to use it.

$ git clone https://github.com/jedisct1/dnscrypt-proxy

$ cd dnscrypt-proxy/utils/generate-domains-blacklists

$ python generate-domains-blacklist.py > blacklist.$(date +%F)
Loading data from [file:domains-blacklist-local-additions.txt]
Loading data from [https://easylist-downloads.adblockplus.org/antiadblockfilters.txt]
[...]
Loading data from [https://raw.githubusercontent.com/notracking/hosts-blocklists/master/domains.txt]
Loading data from [file:domains-time-restricted.txt]
Loading data from [file:domains-whitelist.txt]

$ cp blacklist.$(date +%F) ~/build/linux-x86_64/blacklist.txt

$ wc -l blacklist.txt
117838 blacklist.txt

Privoxy

Privoxy is a non-caching web proxy with advanced filtering capabilities for enhancing privacy, modifying web page data and HTTP headers, controlling access, and removing ads and other obnoxious Internet junk.

Install Privoxy on the remote host:

$ sudo apt -y install privoxy

Use my configuration:

$ sudo cp ~/config/privoxy/* /etc/privoxy

Or customize your own.

Restart Privoxy:

$ sudo service privoxy restart

Test Privoxy locally on the remote host:

$ ALL_PROXY=127.0.0.1:8118 curl -I http://p.p/
HTTP/1.1 200 OK
Content-Length: 2500
Content-Type: text/html
Cache-Control: no-cache
Date: Sun, 01 May 2016 00:00:00 GMT
Last-Modified: Sun, 01 May 2016 00:00:00 GMT
Expires: Sat, 17 Jun 2000 12:00:00 GMT
Pragma: no-cache

Clients can use the remote proxy with Secure Shell tunneling, also known as a "poor man's VPN"

Note AllowTcpForwarding yes must be enabled in /etc/ssh/sshd_config on the server to use these features, followed by sudo service ssh restart.

$ ssh -NCL 5555:127.0.0.1:8118 duh

In another client terminal:

$ ALL_PROXY='127.0.0.1:5555' curl https://icanhazip.com/
104.197.215.107

Requests will appear in Privoxy logs if logging is enabled:

$ sudo tail -F /var/log/privoxy/logfile

Or to use SSH as a SOCKS proxy:

$ ssh -NCD 7000 duh

In another client terminal:

$ curl --proxy socks5h://127.0.0.1:7000 https://icanhazip.com/
104.197.215.107

Tor

Tor can be used as a public relay or as a private bridge for you and your friends.

Install Tor on the server - by default Tor does not relay nor exit traffic; it only provides a local port for outbound connections.

$ sudo apt -y install tor

Use my configuration:

$ sudo cp ~/config/torrc /etc/tor/torrc

Optional Install and configure nyx, a terminal-based monitor for Tor.

$ sudo service tor stop

$ sudo apt install -y nyx

Or:

$ sudo easy_install pip

$ sudo pip install nyx

Configure a credential:

$ tr -dc '[:alnum:]' < /dev/urandom | fold -w20 | head -n1
dSE9jQLhBnJ5x20V5zd7

$ tor --hash-password dSE9jQLhBnJ5x20V5zd7

$ sudo service tor start

$ nyx

DNS over Tor

Tor can resolve DNS A, AAAA and PTR records anonymously. Add a local address to /etc/tor/torrc:

DNSPort 127.26.255.1:53

Then append server=127.26.255.1 to /etc/dnsmasq.conf and restart both services.

Obfuscation

Obfuscate incoming Tor client traffic by using obfsproxy or another Tor pluggable transport.

Install:

$ sudo apt install obfs4proxy

Or to install the latest version of obfs4proxy manually, first install Golang:

$ sudo apt -y install golang

Create a temporary directory, download and build obfs4proxy:

$ export GOPATH=$(mktemp -d)

$ go get git.torproject.org/pluggable-transports/obfs4.git/obfs4proxy

Confirm it's built and install it:

$ echo $?
0

$ $GOPATH/bin/obfs4proxy -version
obfs4proxy-0.0.12-dev

Note If the build fails, you likely need a more recent version of Go:

$ go get git.torproject.org/pluggable-transports/obfs4.git/obfs4proxy
# github.com/refraction-networking/utls
/tmp/tmp.s8JQjim8W7/src/github.com/refraction-networking/utls/tls.go:106: undefined: time.Until
# golang.org/x/net/http2
/tmp/tmp.s8JQjim8W7/src/golang.org/x/net/http2/server.go:214: h1.IdleTimeout undefined (type *http.Server has no field or method
 IdleTimeout)
/tmp/tmp.s8JQjim8W7/src/golang.org/x/net/http2/server.go:215: h1.IdleTimeout undefined (type *http.Server has no field or method
[...]

$ go version
go version go1.7.4 linux/amd64

$ curl -O https://dl.google.com/go/go1.13.4.linux-amd64.tar.gz

$ sudo tar -C /usr/local -xzf go*gz

$ /usr/local/go/bin/go version
go version go1.13.4 linux/amd64

$ /usr/local/go/bin/go get git.torproject.org/pluggable-transports/obfs4.git/obfs4proxy

Copy the built binary:

$ sudo service tor stop

$ sudo cp $GOPATH/bin/obfs4proxy /usr/local/bin

$ sudo chown debian-tor:debian-tor /usr/local/bin/obfs4proxy

Edit /etc/tor/torrc to include:

ORPort 9993
ExtORPort auto
BridgeRelay 1
ServerTransportPlugin obfs4 exec /usr/local/bin/obfs4proxy
ServerTransportListenAddr obfs4 0.0.0.0:10022

Restart Tor:

$ sudo service tor restart

Verify obfs4proxy is accepting connections:

$ sudo lsof -Pni | grep obfs
obfs4prox 6507 debian-tor    3u  IPv6  62584      0t0  TCP *:10022 (LISTEN)

If obfs4proxy fails to start, check the Tor log. You may need to modify the AppArmor profile to include the binary:

$ tail -n2 /etc/apparmor.d/abstractions/tor
  /usr/local/bin/obfsproxy PUx,
  /usr/local/bin/obfs4proxy Pix,

Restart apparmor:

$ sudo service apparmor restart

Verify connections on the server itself over Tor are working:

$ curl --socks5 127.0.0.1:9050 https://icanhazip.com/
[a Tor exit node IP address]

Update firewall rules to allow the new proxy listening port (in this case, TCP port 10022) for your current IP address range:

$ gcloud compute firewall-rules create obfs4-tcp-10022 --network $NETWORK --allow tcp:10022 \
  --source-ranges $(curl -sq https://icanhazip.com/)

If Tor did not start, try starting it manually (sudo may be required to bind to privileged ports):

$ tor -f /etc/tor/torrc

Copy the bridgeline and complete the external IP address and port number:

$ sudo tail -n1 /var/lib/tor/pt_state/obfs4_bridgeline.txt
Bridge obfs4 <IP ADDRESS>:<PORT> <FINGERPRINT> cert=4ar[...]8FA iat-mode=0

$ echo $(curl -s https://icanhazip.com/ ; echo : ; sudo lsof -Pni | grep obf | sed -e "s/.*://" -e "s/ .*//") | tr -d " "
104.197.215.107:10022

$ sudo tail -n1 /var/lib/tor/pt_state/obfs4_bridgeline.txt | awk '{print $1,$2,"104.197.215.107:10022",$(NF-1),$(NF)}'
Bridge obfs4 104.197.215.107:10022 cert=4ar[...]8FA iat-mode=0

To connect from a client, edit torrc to use the IP address and assigned port, for example:

UseBridges 1
Bridge obfs4 104.197.215.107:10022 cert=4ar[...]8FA iat-mode=0

Using Tor Browser, select Configure and Enter custom bridges:

Onion Service

To host an Onion Service, append the following lines to /etc/tor/torrc on the server - for example, to use with a Web server on localhost:

HiddenServiceDir /var/lib/tor/hidden_service/
HiddenServicePort 80 127.0.0.1:80

Restart Tor:

$ sudo service tor restart

Get the service hostname:

$ sudo cat /var/lib/tor/hidden_service/hostname
pqccxgxxxxxxxl5h.onion

You can also host services like ssh as a onion service.

To generate a specific .onion hostname, some software exists.

Certificates

Set up a public-key infrastructure to use your own keys and certificates for VPN, an HTTPS-enabled Web server, etc.

To create a certificate authority, server and client certificates, download the following script.

It is recommended to generate keys in a local, trusted computing environment, preferably air-gapped, or using a live OS image.

$ mkdir ~/pki && cd ~/pki

$ cp ~/config/scripts/pki.sh pki/

Read through and edit the script and variables, especially CN_ ones, to your suit your needs:

$ vim pki.sh

Make the script executable:

$ chmod +x pki.sh

Change OpenSSL certificate requirements to disable mandatory location fields:

$ sudo sed -i.bak "s/= match/= optional/g" /usr/lib/ssl/openssl.cnf

Run the script, accepting prompts with y to sign certificates and commit changes:

$ ./pki.sh
Generating RSA private key, 4096 bit long modulus
........................................................................++
.....................................++
[...]
Sign the certificate? [y/n]:y

If there were no errors, the script created private and public keys for a certificate authority, a server and a client - along with certificate request (srl) and configuration files (cnf).

To check a certificate file (.pem extension) with OpenSSL:

$ openssl x509 -in ca.pem -noout -subject -issuer -enddate
subject= /CN=4CC90cC34b
issuer= /CN=4CC90cC34b
notAfter=Dec 1 00:00:00 2020 GMT

You could also use OpenVPN/easy-rsa or Let's Encrypt.

OpenVPN

OpenVPN is free, open source TLS-based VPN server and client software.

Starting with the client, install OpenVPN:

$ sudo apt -y install openvpn

Use my configuration:

$ sudo cp ~/config/openvpn/server.ovpn /etc/openvpn

Or customize your own.

Preferably client-side (where there is more entropy available), generate a static key so that only trusted clients can attempt connections (extra authentication on top of TLS):

$ openvpn --genkey --secret ta.key

Also client-side, create Diffie-Hellman key exchange parameters:

$ openssl dhparam -dsaparam -out dh.pem 4096

Copy the following files from the previous section to the server. Note that the only private key sent remotely is for the server itself (server.key):

$ scp ta.key dh.pem ca.pem server.pem server.key duh:~

On the server, move the files into place:

$ sudo mkdir /etc/pki

$ sudo mv ca.pem server.pem server.key dh.pem ta.key /etc/pki/

$ sudo chmod 0400 /etc/pki/server.key /etc/pki/ta.key /etc/pki/dh.pem

Enable IP forwarding and make the change permanent:

$ sudo sysctl -w net.ipv4.ip_forward=1

$ echo "net.ipv4.ip_forward = 1" | sudo tee --append /etc/sysctl.conf

Enable NAT for VPN clients:

$ sudo iptables -t nat -A POSTROUTING -o eth0 -s 10.8.0.0/16 -j MASQUERADE

Optional Route all HTTP (TCP port 80) traffic through Privoxy.

$ sudo iptables -t nat -A PREROUTING --source 10.8.0.0/16 -p tcp -m tcp --dport 80 -j DNAT --to 10.8.0.1:8118

Make the firewall rules permanent:

$ sudo apt -y install iptables-persistent

$ sudo iptables-save | sudo tee /etc/iptables/rules.v4

Append 10.8.0.1 as a Dnsmasq listening address and restart the services:

$ sudo sed -i.bak "s/listen-address=127.0.0.1/listen-address=127.0.0.1,10.8.0.1/g" /etc/dnsmasq.conf

$ sudo service dnsmasq restart

$ sudo service openvpn restart

Check the OpenVPN log:

$ sudo tail -F /var/log/openvpn.log
TUN/TAP device tun0 opened
TUN/TAP TX queue length set to 100
do_ifconfig, tt->ipv6=0, tt->did_ifconfig_ipv6_setup=0
/sbin/ip link set dev tun0 up mtu 1500
/sbin/ip addr add dev tun0 10.8.0.1/24 broadcast 10.8.0.255
UDPv4 link local (bound): [undef]
UDPv4 link remote: [undef]
IFCONFIG POOL: base=10.8.0.2 size=252, ipv6=0
Initialization Sequence Completed

If OpenVPN still fails due to unknown ciphers, you may need to install a newer OpenVPN server version - see OpenvpnSoftwareRepos.

Update the remote hosts firewall rules to allow the new VPN listening port (in this case, UDP port 443).

For each connecting device, edit a client configuration using my configuration:

$ mkdir ~/vpn

$ cd ~/vpn

$ cp ~/config/openvpn/client.ovpn .

Add the CA certificate, client certificate and client key material to the configuration:

$ (echo "<ca>" ; cat ~/pki/ca.pem ; echo "</ca>\n<cert>" ; cat ~/pki/client.pem; echo "</cert>\n<key>" ; cat ~/pki/client.key ; echo "</key>") >> client.ovpn

Install and start OpenVPN:

$ sudo apt -y install openvpn

$ cd ~/vpn

$ sudo openvpn --config client.ovpn
[...]
TLS: Initial packet from [AF_INET]104.197.215.107:443, sid=6901c819 3e11276e
VERIFY OK: depth=2, CN=Duh Authority
Validating certificate key usage
++ Certificate has key usage  00a0, expects 00a0
VERIFY KU OK
Validating certificate extended key usage
++ Certificate has EKU (str) TLS Web Server Authentication, expects TLS Web Server Authentication
VERIFY EKU OK
VERIFY OK: depth=0, CN=duh.to
[...]

Verify the local IP address is the same as the remote host:

$ curl -4 https://icanhazip.com/
104.197.215.107

Note If IPv6 is disabled, the connection may fail - you'll need to disable these options on the server to connect:

#server-ipv6 2001:db8:123::/64
#push "route-ipv6 2000::/3"

To connect from Android, install OpenVPN Connect.

Copy client.ovpn and ta.key to a directory on the Android device using adb or Android File Transfer.

Select Import > Import Profile from SD card and select client.ovpn, perhaps in the Download folder.

If the profile was was successfully imported, select Connect.

Start OpenVPN:

$ sudo ~/homebrew/sbin/openvpn --config client.ovpn
OpenVPN 2.4.4 x86_64-apple-darwin16.7.0 [SSL (OpenSSL)] [LZO] [LZ4] [PKCS11] [MH/RECVDA] [AEAD] built on Oct  2 2017
[...]
TLS: Initial packet from [AF_INET]104.197.215.107:443, sid=db4ecf82 4e4e4c5b
VERIFY OK: depth=2, CN=Duh Authority
Validating certificate key usage
++ Certificate has key usage  00a0, expects 00a0
VERIFY KU OK
Validating certificate extended key usage
++ Certificate has EKU (str) TLS Web Server Authentication, expects TLS Web Server Authentication
VERIFY EKU OK
VERIFY OK: depth=0, CN=duh.to
[...]
Initialization Sequence Completed

Verify traffic is routed through the remote host:

$ curl -4 https://icanhazip.com/
104.197.215.107

Web Server

Optional You may want to run a Web server to serve static or dynamic pages.

Install Lighttpd with ModMagnet:

$ sudo apt -y install lighttpd lighttpd-mod-magnet

Use my configuration:

$ sudo cp ~/config/lighttpd/lighttpd.conf /etc/lighttpd

$ sudo cp ~/config/lighttpd/magnet.luau /etc/lighttpd

Or customize your own.

Note Lighttpd expects the server private key and certificate to be stored in one file as the ssl.pemfile argument:

$ sudo cat /etc/pki/server.key /etc/pki/server.pem | sudo tee /etc/pki/lighttpd.pem

You may need to comment out the following line in /etc/lighttpd/lighttpd.conf in order to accept requests on Internet-facing interfaces:

#server.bind = "127.0.0.1"

Restart Lighttpd:

$ sudo service lighttpd restart

Check that it's running - look for the process listening on TCP ports 80 or 443:

$ sudo lsof -Pni | grep lighttpd
lighttpd  3291   www-data    4u  IPv4  18206      0t0  TCP *:80 (LISTEN)
lighttpd  3291   www-data    5u  IPv4  18207      0t0  TCP *:443 (LISTEN)

If it failed to start, try running it directly to check for errors:

$ sudo lighttpd -f /etc/lighttpd/lighttpd.conf -D

Update firewall rules to allow the new HTTP/HTTPS listening port(s) (in this example, TCP port 80 and 443).

Create some content:

$ echo "Hello, World" | sudo tee /var/www/index.html

Once Lighttpd is running, request a page from the server in a Web browser or by using cURL:

$ curl -vv http://duh.to/
Hello, World

You can use client certificates as a means of authentication and authorization, rather than relying on user-provided passwords. See my Lighttpd configuration for an example.

XMPP

Run your own XMPP chat server with Prosody. Client can use Off The Record (OTR) messaging, a form of secure messaging which includes encryption, authentication, deniability and perfect forward secrecy, to communicate privately.

Install Prosody:

$ sudo apt -y install prosody

Use my configuration and edit it to suit your needs:

$ sudo cp ~/config/prosody.cfg.lua /etc/prosody

Or customize your own. See also Advanced ssl config.

Use Diffie-Hellman key exchange parameters from the Certificate steps:

$ sudo cp ~/pki/dh.pem /etc/pki/dh.pem

Copy the server certificate and key from the Certificate steps:

$ sudo cp ~/pki/server.pem /etc/pki/xmpp-cert.pem

$ sudo cp ~/pki/server.key /etc/pki/xmpp-key.pem

Append the CA to the server certificate:

$ cd ~/pki && cat server.pem ca.pem | sudo tee /etc/pki/xmpp-cert.pem

Or generate a new self-signed certificate:

$ sudo openssl req -x509 -newkey rsa:4096 -days 365 -sha512 -subj "/CN=server.name" \
  -nodes -keyout /etc/pki/xmpp-key.pem -out /etc/pki/xmpp-cert.pem

Set file ownership:

$ sudo chown prosody:prosody /etc/pki/xmpp-*.pem

Restart Prosody:

$ sudo service prosody restart

Ensure it's running and listening:

$ sudo tail -n1 /var/log/prosody/prosody.log
mod_posix       info    Successfully daemonized to PID 1831

$ sudo lsof -Pni | grep prosody
lua5.1     1831    prosody    6u  IPv6 317986      0t0  TCP *:5269 (LISTEN)
lua5.1     1831    prosody    7u  IPv4 317987      0t0  TCP *:5269 (LISTEN)
lua5.1     1831    prosody    8u  IPv6 317990      0t0  TCP *:5222 (LISTEN)
lua5.1     1831    prosody    9u  IPv4 317991      0t0  TCP *:5222 (LISTEN)

Update firewall rules to allow the new prosody listening ports (in this example, TCP ports 5222 and 5269):

$ gcloud compute firewall-rules create xmpp-tcp-5222-5269 --network $NETWORK \
  --allow tcp:5222,tcp:5269 --source-ranges $(curl -s https://icanhazip.com/)

Create a new user:

$ sudo prosodyctl adduser [email protected]

Important The domain name must match the server certificate common name (CN_SERVER in pki.sh) - check with sudo openssl x509 -in /etc/pki/xmpp-cert.pem -noout -subject

Federating

For others to communicate with your XMPP server, you must configure DNS records for interdomain federation:

_xmpp-client._tcp of type SRV with data 0 5 5222 duh.to.

_xmpp-server._tcp of type SRV with data 0 5 5269 duh.to.

After a little while, check domain SRV records:

$ dig +short srv _xmpp-server._tcp.duh.to
0 5 5269 duh.to.

$ dig +short srv _xmpp-client._tcp.duh.to
0 5 5222 duh.to.

Using

To connect from a client, use Profanity

$ sudo apt -y install profanity

$ profanity

Log in by typing /connect [email protected] and entering the password when prompted.

Generate OTR keys by typing /otr gen - this part may take a while.

Send a message to a contact by typing /msg [email protected] - to navigate tabs, use /win 1, /win 2, etc.

To start OTR, type /otr start - Profanity will show OTR session started (untrusted).

To authenticate the chat partner, type /otr question foo? bar where bar is an answer to foo? which only the person you assume to be speaking with can answer. If the person answers correctly, Profanity will show Authentication successful followed by OTR session trusted - now you can be sure the connection is encrypted and authenticated.

Or use agl/xmpp-client:

$ go get github.com/agl/xmpp-client

$ $GOPATH/bin/xmpp-client

If you can't connect, check for errors in /var/log/prosody/prosody.err on the server.

To verify the SHA256 fingerprint matches the certificate on the server:

$ openssl x509 -in /etc/pki/xmpp-cert.pem -fingerprint -noout -sha256

To view and verify the XMPP server's certificate fingerprint remotely, use the openssl command from a client:

$ echo -e | openssl s_client -connect duh.to:5222 -starttls xmpp | openssl x509 -noout -fingerprint -sha256 | tr -d ':'
[...]
SHA256 Fingerprint=9B759D41E3DE30F9D2F902027D792B65D950A98BBB6D6D56BE7F2528453BF8E9

Note If using agl/xmpp-client and custom certificates (i.e., not signed by a trusted root CA), you will need to manually add the server's SHA256 fingerprint to ~/.xmpp-client, like:

"ServerCertificateSHA256": "9B759D41E3DE30F9D2F902027D792B65D950A98BBB6D6D56BE7F2528453BF8E9"

If an error occurs while attempting to connect, check /var/log/prosody/prosody.err on the server.

Finish

Reboot the instance and make sure everything still works. If not, you'll need to automate certain programs to start up on their own (for example, Privoxy will fail to start if OpenVPN does not first create a tunnel interface to bind to).

With this guide, a secure server with several privacy- and security-enhancing services can be setup in less than an hour. The server can be used to circumvent firewalls, provide strong encryption and overall improve online experience, all for a low monthly cost (less than $1 per day). Consider using Preemptible VM instances which can be started right back up with a script to lower costs.

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