Turn RPi into WAP

Instruction is based on Kali Revealed course by great guys from Offensive Security team.

Prepare

Tool	Description
Raspberry Pi 3+	Single-board computer with wireless LAN and Bluetooth connectivity.
Kali Linux Official ARM image	"... the same build infrastructure as the official Kali releases for ARM architecture."
hostapd	Service which creates Access Point.
dnsmasq	Service responsible for DNS forwarding and providing DHCP server.
dhcpcd5	A DHCP client.

File	Description
/etc/dhcpcd.conf	DHCP service configuration file. Used to ignore wlan0 setup.
/etc/network/interfaces	Used to setup wlan0 interface.
/etc/hostapd/hostapd.conf	hostapd service configuration file. Used to setup AP parameters.
/etc/default/hostapd	Stores path to necessary hostapd configuration file.
/etc/dnsmasq.conf	Used to configure dnsmasq service.
/proc/sys/net/ipv4/ip_forward	Store IP forwarding parameter permanently.
/etc/rc.local	Used to reload iptables rules after reboot.

Install Kali on rpi

1. Download latest image version from Kali official website.
2. Verify checksum.

shasum -a 256 path/to/file

1. Copy downloaded image on microSD card with dd command:

dd if=kali-image.img of=/dev/something bs=512k status=progress

Default credentials: kali, kali.

Configure Access Point

• Install required packages:

sudo apt-get install dnsmasq hostapd dhcpcd5

• Tell dhcpcd to ignore wlan0 setup. Add the following directive before any interface settings denyinterfaces wlan0:

sudo nano /etc/dhcpcd.con

• Setup wifi interface:

sudo nano /etc/network/interfaces

allow-hotplug wlan0
iface wlan0 inet static
    address 172.24.1.1
    netmask 255.255.255.0
    network 172.24.1.0
    broadcast 172.24.1.255

• Restart dhcpcd and reload the configuration of wlan0:

sudo service dhcpcd restart

sudo ifdown wlan0; sudo ifup wlan0

• Configure hostapd:

sudo nano /etc/hostapd/hostapd.conf

Parameter	Value	Description
interface	wlan0	The name of the WiFi interface configured above.
driver	nl80211	Use the nl80211 driver with the brcmfmac driver.
hw_mode	g	Use the 2.4GHz band.
channel	6	Use channel 6.
ieee80211n	1	Enable 802.11n.
wmm_enabled	1	Enable WMM.
ht_capab	[HT40][SHORT-GI-20][DSSS_CCK-40]	Enable 40MHz channels with 20ns guard interval.
macaddr_acl	0	Accept all MAC addresses.
auth_algs	1	Use WPA authentication.
ignore_broadcast_ssid	0	Require clients to know the network name.
ssid	Kali-Pi3	The name of the network.
wpa	2	Use WPA2.
wpa_key_mgmt	WPA-PSK	Use a pre-shared key.
wpa_passphrase	paSSphras8	The network passphrase.
rsn_pairwise	CCMP	Use AES, instead of TKIP.

• Test Wireless Access Point works:

sudo /usr/sbin/hostapd /etc/hostapd/hostapd.conf

• Specify dhcpcd configuration file place. Uncomment line and set DAEMON_CONF="/etc/hostapd/hostapd.conf":

sudo nano /etc/default/hostapd

Configure DNS forwarding

• Setup dnsmasq:

sudo mv /etc/dnsmasq.conf /etc/dnsmasq.conf.orig

sudo nano /etc/dnsmasq.conf

Parameter	Value	Description
interface	wlan0	Use interface wlan0.
listen-address	172.24.1.1	Set listening address from /etc/network/interfaces.
bind-interfaces		Bind to the interface to make sure we aren't sending things elsewhere.
server	1.1.1.1	Forward DNS requests to Cloudflare DNS.
domain-needed		Don't forward short names.
bogus-priv		Never forward addresses in the non-routed address spaces.
dhcp-range	172.24.1.50,172.24.1.150,12h	Assign IP addresses between 172.24.1.50 and 172.24.1.150 with a 12 hour lease time.

Now, we have two interfaces active, and we have a DHCP client for our Pi and a DHCP server for our wireless guests. Now we need to forward traffic between the Wi-Fi and Ethernet interfaces.

Configure Wi-Fi - Ethernet forwarding

• Update /proc:

echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward

• Make change permanent through sysctl:

sudo nano /etc/sysctl.conf

• Uncomment the line containing net.ipv4.ip_forward=1.

Configure iptables

Whenever a new connection is encountered (-t nat), we want to alter the packets as they are about to go out (-A POSTROUTING) on our Ethernet interface (-o eth0). The -j MASQUERADE target masks private IP address of the client with the external IP address of the firewall/gateway (Kali Pi).

sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

Append -A rule to the FORWARD chain packets (packets being routed through the Pi) which accepts -j ACCEPT packets from eth0 to wlan0 - -i eth0 -o wlan0 that belong to ESTABLISHED or are RELATED to existing position.

sudo iptables -A FORWARD -i eth0 -o wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT

Forward and accept all packets form wlan0 to eth0.

sudo iptables -A FORWARD -i wlan0 -o eth0 -j ACCEPT

• Check out rules:

sudo iptables -S

• Save rules to file:

sudo iptables-save | sudo tee /etc/iptables.ipv4.nat

• Apply these rules every time we boot the Pi by editing the /etc/rc.local file:

sudo nano /etc/rc.local

#!/bin/sh -e
iptables-restore < /etc/iptables.ipv4.nat

• Make the file executable:

sudo chmod 711 /etc/rc.local

Enable configured services

sudo systemctl enable hostapd dnsmasq

Reboot and check that everything works fine.