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README.md

How to self-host a hardened strongSwan IKEv2/IPsec VPN server for iOS and macOS

Heads up: when following this guide on IPv4-only servers (which is totally fine if one knows what we are doing), it’s likely IPv6 traffic will leak on iOS when clients are connected to carriers or ISPs running dual stack (IPv4 + IPv6) infrastructure. Leaks can be mitigated on iOS (cellular-only) and on macOS by following this guide.

Requirements

  • Virtual private server (VPS) or dedicated server running Debian 10 (buster)
  • Computer running macOS Mojave or Catalina
  • Phone running iOS 12 or 13

Guide

Step 1: create SSH key pair used to setup server

For increased security, protect private key using strong passphrase.

When asked for file in which to save key, enter vpn-server.

$ cd ~/.ssh
$ ssh-keygen -t rsa -C "vpn-server"
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/sunknudsen/.ssh/id_rsa): vpn-server
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in vpn-server.
Your public key has been saved in vpn-server.pub.
The key fingerprint is:
SHA256:4On7WymZIcM5p8SbsybwJpaFIUrnTUMf/1fdAhI1WPY vpn-server
The key's randomart image is:
+---[RSA 3072]----+
|          .==    |
|     . .  o..o   |
|    . o o  . .E o|
|.... * = .    ..o|
|o.ooo % S .   .. |
|. o..+ O + o .   |
|   =  * + o .    |
|  + + .+ o       |
| . o oo.o.       |
+----[SHA256]-----+

Step 2: log in to the server as root

Replace 185.193.126.203 with IP of server.

If server uses password authentication, run the following and type in password.

ssh root@185.193.126.203

If server uses public key authentication (using the key pair from step 1), run the following and type in passphrase.

ssh root@185.193.126.203 -i ~/.ssh/vpn-server

Step 3: add SSH public key to authorized_keys

This step is required only if server was configured without public key authentication.

When copy/pasting commands that start with cat << "EOF", select all lines (from cat << "EOF" to EOF) at once as they are part of the same (single) command

On Mac, run:

echo "cat << \"EOF\" > ~/.ssh/authorized_keys
$(cat ~/.ssh/vpn-server.pub)
EOF"

On server, paste output from macOS command and press enter.

cat << "EOF" > ~/.ssh/authorized_keys
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABgQCu4k9OcJlatGgUoo41m18Hekv+nSHq1w7qcuAuOZWLI8y5aYkLzyEgyp7EibB0rcmwiZfwx/RDb5zAvlr9KGsOWOYJ/gRIf4AwK1PdBPDo8jaa02J/H585NHV7T7XJ7Ycl/LeJh+oDXGs4OOspiFM/7NuleqCA0sSuJEnnuuTZsIDAlJwtWIJTM8lg4nWCQx2xAGkRyx4eNHE2vmlg+xHu3PbHg9kpSIaBWpx0WsysypyaB77+pkid6kYzxPXexoxFm4FnkoY7PZGb97wl4FwW1EK/yo9rnwbtEq5ny96JEHqeJdxeBGHYrsAoRro4jPWYXvdXZV2s27NYC6S3yHsJdaLfyfJXyTaygOyyaf39GcwqfJZpmVYwVyfZ2Go6ec9R/dFbKEA4Ue7aeCkDskSTiMuUZjYjfhezpa4Y0Jiy+lDZFVSv3tsBYu7Nxq0erZ2ygRJAXUMvvyFICJQGUhblRGXAOwYUt72CSUM0ZMsr84aOWsyzRwVQXzxETuDgnXk= vpn-server
EOF

On server, confirm the output from cat ~/.ssh/authorized_keys matches the output from cat ~/.ssh/vpn-server.pub on macOS.

Step 4: create vpn-server-admin user

When asked for password, use output from openssl rand -base64 24 (and store password in password manager). For all other fields, press enter. Then press y.

adduser vpn-server-admin

Step 5: copy root’s authorized_keys file over to vpn-server-admin’s home folder.

mkdir /home/vpn-server-admin/.ssh
cp /root/.ssh/authorized_keys /home/vpn-server-admin/.ssh/authorized_keys
chown -R vpn-server-admin:vpn-server-admin /home/vpn-server-admin/.ssh

Step 6: set root password

When asked for password, use output from openssl rand -base64 24 (and store password in password manager).

passwd

Step 7: log out

exit

Step 8: log in as vpn-server-admin

Replace 185.193.126.203 with IP of server.

ssh vpn-server-admin@185.193.126.203 -i .ssh/vpn-server

Step 9: switch to root

When asked, enter root password.

su -

Step 10: update SSH config to disable root login and password authentication and restart SSH daemon

sed -i -E 's/(#)?PermitRootLogin (prohibit-password|yes)/PermitRootLogin no/' /etc/ssh/sshd_config
sed -i -E 's/(#)?PasswordAuthentication yes/PasswordAuthentication no/' /etc/ssh/sshd_config
systemctl restart ssh

Step 11: update apt and upgrade packages

apt update
apt upgrade -y

Step 12: install and configure vim

apt install -y vim
cat << "EOF" > ~/.vimrc
set encoding=UTF-8
set termencoding=UTF-8
set nocompatible
set backspace=indent,eol,start
set autoindent
set tabstop=2
set shiftwidth=2
set expandtab
set smarttab
set ruler
set paste
syntax on
EOF

Step 13: set timezone (the following command is for Montreal time)

See https://en.wikipedia.org/wiki/List_of_tz_database_time_zones for available timezones.

timedatectl set-timezone America/Montreal

Step 14: install curl and python and generate random IPv6 ULA

Shout out to Andrew Ho for ulagen.py.

The following code block downloads and runs ulagen.py (optionally download ulagen.py.sig to verify signature).

$ apt install -y curl python
$ curl -s https://sunknudsen.com/static/media/privacy-guides/how-to-self-host-a-hardened-strongswan-ikev2-ipsec-vpn-server-for-ios-and-macos/ulagen.py | python
Prefix:       fdc7:da04:1ee6::/48
First subnet: fdc7:da04:1ee6::/64
Last subnet:  fdc7:da04:1ee6:ffff::/64

Step 15: install iptables-persistent

When asked to save current IPv4 or IPv6 rules, answer Yes.

apt install -y iptables-persistent

Step 16: configure iptables

Replace eth0 (if needed) and fdc7:da04:1ee6::/64 with first subnet of step 14 (to display available interfaces, run ip a).

iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -p tcp --dport 22 -j ACCEPT
iptables -A INPUT -p udp --dport 500 -j ACCEPT
iptables -A INPUT -p udp --dport 4500 -j ACCEPT
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -s 10.0.2.0/24 -m policy --dir in --pol ipsec --proto esp -j ACCEPT
iptables -A FORWARD -d 10.0.2.0/24 -m policy --dir out --pol ipsec --proto esp -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
iptables -A OUTPUT -p tcp --dport 53 -m state --state NEW -j ACCEPT
iptables -A OUTPUT -p udp --dport 53 -m state --state NEW -j ACCEPT
iptables -A OUTPUT -p tcp --dport 80 -m state --state NEW -j ACCEPT
iptables -A OUTPUT -p tcp --dport 443 -m state --state NEW -j ACCEPT
iptables -A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -t nat -A POSTROUTING -s 10.0.2.0/24 -o eth0 -m policy --pol ipsec --dir out -j ACCEPT
iptables -t nat -A POSTROUTING -s 10.0.2.0/24 -o eth0 -j MASQUERADE
iptables -t mangle -A FORWARD -m policy --pol ipsec --dir in -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 1280
iptables -t mangle -A FORWARD -m policy --pol ipsec --dir out -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 1280
iptables -P FORWARD DROP
iptables -P INPUT DROP
iptables -P OUTPUT DROP

If the server is IPv4-only, run:

ip6tables -P FORWARD DROP
ip6tables -P INPUT DROP
ip6tables -P OUTPUT DROP

If the server is dual stack (IPv4 + IPv6) run:

ip6tables -A INPUT -i lo -j ACCEPT
ip6tables -A INPUT -p ipv6-icmp -j ACCEPT
ip6tables -A INPUT -p udp --dport 500 -j ACCEPT
ip6tables -A INPUT -p udp --dport 4500 -j ACCEPT
ip6tables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
ip6tables -A FORWARD -s fdc7:da04:1ee6::/64 -m policy --dir in --pol ipsec --proto esp -j ACCEPT
ip6tables -A FORWARD -d fdc7:da04:1ee6::/64 -m policy --dir out --pol ipsec --proto esp -j ACCEPT
ip6tables -A OUTPUT -o lo -j ACCEPT
ip6tables -A OUTPUT -p ipv6-icmp -j ACCEPT
ip6tables -A OUTPUT -p tcp --dport 53 -m state --state NEW -j ACCEPT
ip6tables -A OUTPUT -p udp --dport 53 -m state --state NEW -j ACCEPT
ip6tables -A OUTPUT -p tcp --dport 80 -m state --state NEW -j ACCEPT
ip6tables -A OUTPUT -p tcp --dport 443 -m state --state NEW -j ACCEPT
ip6tables -A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
ip6tables -t nat -A POSTROUTING -s fdc7:da04:1ee6::/64 -o eth0 -m policy --pol ipsec --dir out -j ACCEPT
ip6tables -t nat -A POSTROUTING -s fdc7:da04:1ee6::/64 -o eth0 -j MASQUERADE
ip6tables -t mangle -A FORWARD -m policy --pol ipsec --dir in -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 1280
ip6tables -t mangle -A FORWARD -m policy --pol ipsec --dir out -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 1280
ip6tables -P FORWARD DROP
ip6tables -P INPUT DROP
ip6tables -P OUTPUT DROP

ip6tables -A FORWARD -p tcp -m policy --pol ipsec --dir in -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 1280

Step 17: log out and log in to confirm iptables didn’t block SSH

exit
exit

When asked, enter root password.

ssh vpn-server-admin@185.193.126.203 -i .ssh/vpn-server
su -

Step 18: make iptables rules persistent

iptables-save > /etc/iptables/rules.v4
ip6tables-save > /etc/iptables/rules.v6

Step 19: switch DNS nameservers over to privacy-conscious 1.1.1.1

Using 1.1.1.1 is optional but the default for this guide.

If the server is IPv4-only, run:

cp /etc/resolv.conf /etc/resolv.conf.backup
cat << "EOF" > /etc/resolv.conf
nameserver 1.1.1.1
nameserver 1.0.0.1
EOF

If the server is dual stack (IPv4 + IPv6) run:

cp /etc/resolv.conf /etc/resolv.conf.backup
cat << "EOF" > /etc/resolv.conf
nameserver 1.1.1.1
nameserver 1.0.0.1
nameserver 2606:4700:4700::1111
nameserver 2606:4700:4700::1001
EOF

Step 20: add dummy network interface

cp /etc/network/interfaces /etc/network/interfaces.backup
cat << "EOF" >> /etc/network/interfaces

auto strongswan0
iface strongswan0 inet static
  address 10.0.2.1/24
  pre-up ip link add strongswan0 type dummy
EOF

Step 21: install dnsmasq

apt install -y dnsmasq

Step 22: configure dnsmasq

cat << "EOF" > /etc/dnsmasq.d/01-dhcp-strongswan.conf
interface=strongswan0
dhcp-range=10.0.2.10,10.0.2.254,255.255.255.0
port=0
EOF

Step 23: restart dnsmasq

systemctl restart dnsmasq

Step 24: install strongSwan

If you are shown an "Old runlevel management superseded" warning, answer Ok.

apt install -y strongswan libcharon-extra-plugins

Step 25: configure strongSwan

Replace fdc7:da04:1ee6::/64 with first subnet of step 14

Backup and override /etc/ipsec.conf

cp /etc/ipsec.conf /etc/ipsec.conf.backup

If the server is IPv4-only, run:

cat << "EOF" > /etc/ipsec.conf
config setup
  charondebug="ike 1, knl 1, cfg 1"
  uniqueids=never

conn ikev2
  auto=add
  compress=no
  type=tunnel
  keyexchange=ikev2
  fragmentation=yes
  forceencaps=yes
  ike=aes256gcm16-prfsha512-ecp384!
  esp=aes256gcm16-ecp384!
  dpdaction=clear
  dpddelay=300s
  rekey=no
  left=%any
  leftid=vpn-server.com
  leftcert=vpn-server.crt
  leftsendcert=always
  leftsubnet=0.0.0.0/0
  right=%any
  rightid=%any
  rightauth=eap-tls
  rightdns=1.1.1.1,1.0.0.1
  rightsourceip=%dhcp
  rightsendcert=never
  eap_identity=%identity
EOF

If the server is dual stack (IPv4 + IPv6) run:

cat << "EOF" > /etc/ipsec.conf
config setup
  charondebug="ike 1, knl 1, cfg 1"
  uniqueids=never

conn ikev2
  auto=add
  compress=no
  type=tunnel
  keyexchange=ikev2
  fragmentation=yes
  forceencaps=yes
  ike=aes256gcm16-prfsha512-ecp384!
  esp=aes256gcm16-ecp384!
  dpdaction=clear
  dpddelay=300s
  rekey=no
  left=%any
  leftid=vpn-server.com
  leftcert=vpn-server.crt
  leftsendcert=always
  leftsubnet=0.0.0.0/0
  right=%any
  rightid=%any
  rightauth=eap-tls
  rightdns=1.1.1.1,1.0.0.1,2606:4700:4700::1111,2606:4700:4700::1001
  rightsourceip=%dhcp,fdc7:da04:1ee6::/64
  rightsendcert=never
  eap_identity=%identity
EOF

Backup and override /etc/ipsec.secrets

cp /etc/ipsec.secrets /etc/ipsec.secrets.backup
cat << "EOF" > /etc/ipsec.secrets
: RSA vpn-server.key
EOF

Backup and override /etc/strongswan.d/charon-logging.conf

cp /etc/strongswan.d/charon-logging.conf /etc/strongswan.d/charon-logging.conf.backup
cat << "EOF" > /etc/strongswan.d/charon-logging.conf
charon {
    filelog {
        charon {
            default = 1
        }
    }
    syslog {
        auth {
            default = 1
        }
    }
}
EOF

Backup and override /etc/strongswan.d/charon/dhcp.conf

cp /etc/strongswan.d/charon/dhcp.conf /etc/strongswan.d/charon/dhcp.conf.backup
cat << "EOF" > /etc/strongswan.d/charon/dhcp.conf
dhcp {
    force_server_address = yes
    identity_lease = yes
    interface = lo
    load = yes
    server = 10.0.2.1
}
EOF

Disable unused plugins

cd /etc/strongswan.d/charon
sed -i 's/load = yes/load = no/g' ./*.conf
sed -i 's/load = no/load = yes/g' ./eap-tls.conf ./aes.conf ./dhcp.conf ./farp.conf ./gcm.conf ./hmac.conf ./kernel-netlink.conf ./nonce.conf ./openssl.conf ./pem.conf ./pgp.conf ./pkcs12.conf ./pkcs7.conf ./pkcs8.conf ./pubkey.conf ./random.conf ./revocation.conf ./sha2.conf ./socket-default.conf ./stroke.conf ./x509.conf

Step 26: create certificate authority (for security reasons, this is done on macOS rather than on server)

Create certificate-authority folder on desktop

mkdir ~/Desktop/certificate-authority
cd ~/Desktop/certificate-authority

Create OpenSSL config file (edit defaults if needed)

cat << "EOF" > openssl.cnf
[ req ]
distinguished_name = req_distinguished_name
attributes = req_attributes
[ req_distinguished_name ]
countryName = Country Name (2 letter code)
countryName_min = 2
countryName_max = 2
0.organizationName = Organization Name (eg, company)
commonName = Common Name (eg, fully qualified host name)
commonName_max = 64
countryName_default = CA # Defaults
0.organizationName_default = Self-hosted strongSwan VPN # Defaults
[ req_attributes ]
challengePassword = A challenge password
challengePassword_min = 4
challengePassword_max = 20
[ ca ]
subjectKeyIdentifier = hash
basicConstraints = critical, CA:true
keyUsage = critical, cRLSign, keyCertSign
[ server ]
authorityKeyIdentifier = keyid
subjectAltName = DNS:vpn-server.com # Defaults
extendedKeyUsage = serverAuth, 1.3.6.1.5.5.8.2.2
[ client ]
authorityKeyIdentifier = keyid
subjectAltName = email:client@vpn-server.com # Defaults
extendedKeyUsage = serverAuth, 1.3.6.1.5.5.8.2.2
EOF

Create certificate authority private key

$ openssl genrsa -out ca.key 4096
Generating RSA private key, 4096 bit long modulus
......................................++
........................................................................................................................................................................................................................................................................................++
e is 65537 (0x10001)

Create certificate authority root certificate

When asked for common name, enter vpn-server.com.

$ openssl req -x509 -new -nodes -config openssl.cnf -extensions ca -key ca.key -days 3650 -out ca.crt
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [CA]:
Organization Name (eg, company) [Self-hosted strongSwan VPN]:
Common Name (eg, fully qualified host name) []:vpn-server.com

Create vpn-server private key and certificate

When asked for common name, enter vpn-server.com and press enter to skip challenge password.

$ openssl genrsa -out vpn-server.key 4096
Generating RSA private key, 4096 bit long modulus
.................................................................................................................................................................................................................................................++
................................................................................++
e is 65537 (0x10001)

$ openssl req -new -config openssl.cnf -extensions server -key vpn-server.key -out vpn-server.csr
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [CA]:
Organization Name (eg, company) [Self-hosted strongSwan VPN]:
Common Name (eg, fully qualified host name) []:vpn-server.com

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:

$ openssl x509 -req -extfile openssl.cnf -extensions server -in vpn-server.csr -CA ca.crt -CAkey ca.key -CAcreateserial -days 3650 -out vpn-server.crt
Signature ok
subject=/C=CA/O=Self-hosted strongSwan VPN/CN=vpn-server.com
Getting CA Private Key

Create vpn-client private key and certificate

When asked for common name, enter client@vpn-server.com and press enter to skip challenge password.

$ openssl genrsa -out vpn-client.key 4096
Generating RSA private key, 4096 bit long modulus
.........++
............................................................................++
e is 65537 (0x10001)

$ openssl req -new -config openssl.cnf -extensions client -key vpn-client.key -out vpn-client.csr
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [CA]:
Organization Name (eg, company) [Self-hosted strongSwan VPN]:
Common Name (eg, fully qualified host name) []:client@vpn-server.com

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:

$ openssl x509 -req -extfile openssl.cnf -extensions client -in vpn-client.csr -CA ca.crt -CAkey ca.key -CAcreateserial -days 3650 -out vpn-client.crt
Signature ok
subject=/C=CA/O=Self-hosted strongSwan VPN/CN=client@vpn-server.com
Getting CA Private Key

Create vpn-client PKCS12 archive

When asked for export password, use output from openssl rand -base64 24 (and store password in password manager).

$ openssl pkcs12 -in vpn-client.crt -inkey vpn-client.key -certfile ca.crt -export -out vpn-client.p12
Enter Export Password:
Verifying - Enter Export Password:

Step 27: copy/paste the content of ca.crt, vpn-server.key and vpn-server.crt to server and make private key root-only.

On Mac: run cat ca.crt

On server: run vi /etc/ipsec.d/cacerts/ca.crt, press i, paste output from previous step in the window and press shift+z+z

On Mac: run cat vpn-server.key

On server: run vi /etc/ipsec.d/private/vpn-server.key, press i, paste output from previous step in the window and press shift+z+z

On Mac: run cat vpn-server.crt

On server: run vi /etc/ipsec.d/certs/vpn-server.crt, press i, paste output from previous step in the window and press shift+z+z

On server: run chmod -R 600 /etc/ipsec.d/private

Step 28: start strongSwan

systemctl restart strongswan

Step 29: configure sysctl

Backup and override /etc/sysctl.conf

cp /etc/sysctl.conf /etc/sysctl.conf.backup

If the server is IPv4-only, run:

sed -i -E 's/#net.ipv4.ip_forward=1/net.ipv4.ip_forward=1/' /etc/sysctl.conf
sed -i -E 's/#net.ipv4.conf.all.send_redirects = 0/net.ipv4.conf.all.send_redirects = 0/' /etc/sysctl.conf
cat << "EOF" >> /etc/sysctl.conf
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
EOF

If the server is dual stack (IPv4 + IPv6) run:

sed -i -E 's/#net.ipv4.ip_forward=1/net.ipv4.ip_forward=1/' /etc/sysctl.conf
sed -i -E 's/#net.ipv4.conf.all.accept_redirects = 0/net.ipv4.conf.all.accept_redirects = 0/' /etc/sysctl.conf
sed -i -E 's/#net.ipv4.conf.all.send_redirects = 0/net.ipv4.conf.all.send_redirects = 0/' /etc/sysctl.conf
sed -i -E 's/#net.ipv6.conf.all.forwarding=1/net.ipv6.conf.all.forwarding=1/' /etc/sysctl.conf

Reload sysctl

sysctl -p

Step 30: create VPN profiles for iOS and macOS using Apple Configurator 2

Open "Apple Configurator 2", then click "File", then "New Profile".

In "General", fill out "Name" and "Identifier".

apple-configurator-general

In "Certificates", click "Configure" and select "ca.crt". Then click "+" and select "vpn-client.p12".

The password is the one from step 25.

apple-configurator-certificates

In "VPN", click "Configure" and enter the settings from the following screenshot. The "Child SA Params" are the same as "IKE SA Params".

apple-configurator-vpn

Finally, click "File", then "Save", and save file as "Self-hosted strongSwan VPN.mobileconfig".

Step 31: add VPN profile to macOS

This step is super simple, simply double-click "Self-hosted strongSwan VPN.mobileconfig" and follow instructions.

Step 32: add VPN profile to iOS using Apple Configurator 2

Unlock iPhone, connect it to Mac using USB cable and open Apple Configurator 2.

In "All Devices", double-click on iPhone, then "Add", and finally "Profiles".

Select "Self-hosted strongSwan VPN.mobileconfig" and follow instructions on iPhone.

On iOS, open "Settings", then "Profile Downloaded" and tap "Install"

Step 33: connect to VPN on iOS and macOS