EAP-TTLS-CHAP

What is Expansion of EAP-TTLS-CHAP?

EAP-TTLS-CHAP stands for Extensible Authentication Protocol - Tunneled Transport Layer Security - Challenge Handshake Authentication Protocol.

What is EAP-TTLS-CHAP?

EAP-TTLS-CHAP is an authentication method that combines EAP-TTLS (a tunneling protocol) with CHAP (a password-based challenge-response authentication protocol). EAP-TTLS establishes a secure TLS tunnel, and inside this tunnel, CHAP performs client authentication securely.

Why is EAP-TTLS-CHAP useful?

  • Allows legacy protocols like CHAP to be used securely.

  • Protects user credentials by encrypting authentication data.

  • Supports mutual authentication without requiring client certificates.

  • Useful in enterprise wireless and VPN scenarios.

How it works?

  1. TLS tunnel is created between client and authentication server.

  2. Server sends a CHAP challenge inside the encrypted tunnel.

  3. Client responds with a CHAP response using password hash.

  4. Server verifies and authenticates the client.

  5. Keys are generated for securing the session.

Where is EAP-TTLS-CHAP used?

  • Enterprise wireless networks and VPN access.

  • Environments requiring secure authentication without client certificates.

  • Legacy network infrastructures transitioning to secure protocols.

Which OSI layer does this protocol belong to?

  • Application Layer (Layer 7).

  • Runs over EAP, transported via EAPOL and RADIUS.

IS EAP-TTLS-CHAP windows specific?

  • No, it is platform-independent.

  • Supported on Windows via third-party supplicants.

IS EAP-TTLS-CHAP Linux Specific?

  • No, supported on Linux with supplicants like wpa_supplicant.

Which Transport Protocol is used by EAP-TTLS-CHAP?

  • Uses EAPOL for link-layer transport (Layer 2).

  • RADIUS (UDP) protocol for communication with authentication servers.

Which Port is used by EAP-TTLS-CHAP?

  • UDP port 1812 when using RADIUS.

Is EAP-TTLS-CHAP using Client server model?

  • Yes, involves client (supplicant), authenticator, and authentication server.

Whether EAP-TTLS-CHAP protocol uses certificates?

  • Server certificates are mandatory to establish TLS tunnel.

  • Client certificates generally not required; authentication done via CHAP.

How many frame exchanges are seen during connection for EAP-TTLS-CHAP protocol?

  • Multiple EAPOL frames occur during TLS handshake and CHAP challenge-response.

  • Typically several dozen frames in total.

Whether EAP-TTLS-CHAP Protocol uses client certificates?

  • No, client authentication is based on CHAP inside the TLS tunnel.

Whether EAP-TTLS-CHAP Protocol uses Server Certificates?

  • Yes, server certificates secure the TLS tunnel.

IS EAP-TTLS-CHAP Protocol depends on TCP?

  • No, TCP is not a direct dependency of EAP-TTLS-CHAP.

IS EAP-TTLS-CHAP Protocol depends on UDP?

  • Yes, RADIUS communication typically uses UDP.

What are the roles involved when testing EAP-TTLS-CHAP Protocol?

  • Client (Supplicant)

  • Authenticator (Access Point)

  • Authentication Server (RADIUS)

  • Testing tools like packet capture analyzers and EAP testers.

Does EAP-TTLS-CHAP Protocol work with free radius server on Linux?

  • Yes, FreeRADIUS supports EAP-TTLS with CHAP authentication.

Does EAP-TTLS-CHAP Protocol work with Internal radius server of hostapd?

  • Limited or no support; external RADIUS servers like FreeRADIUS are preferred.

What is the RFC version use for EAP-TTLS-CHAP Protocol?

  • EAP-TTLS: RFC 5281

  • CHAP: RFC 1994

During Connection Procedure which EPoL Packets are encrypted?

  • Inner authentication messages (CHAP challenge-response) are encrypted.

  • TLS handshake packets are not encrypted initially but secure the tunnel.

Can you Explain different stages of Connection Procedure for EAP-TTLS-CHAP Protocol?

  1. TLS tunnel establishment between client and server.

  2. Inner authentication with CHAP challenge and response inside the tunnel.

  3. Authentication success/failure communicated.

  4. Generation of Pairwise Master Key (PMK) for securing wireless session.

What is the final output of Connection Procedure?

  • Authentication result (success or failure).

  • PMK generated to protect subsequent wireless communication.

  • Network access granted if authentication succeeds.

What is the format of the key generate after the connection procedure?

  • A 256-bit Pairwise Master Key (PMK).

Where the use of PMK generated by the Connection Procedure?

  • Used in 4-way handshake to derive session keys for encryption.

  • Secures data transmission between client and access point.

  • In this section, you are going to learn

  • Terminology

  • Version Info

  • rfc details

  • Run Free RADIUS

FreeRADIUS: Download latest freeradius source code

Note

  • Make sure internet is available in laptop to download freeradius package

test:~$ wget https://github.com/FreeRADIUS/freeradius-server/archive/v3.0.x.tar.gz

FreeRADIUS: Extract freeradius

test:~$ tar -zvf v3.0.x.tar.gz

FreeRADIUS: Change directory to Radius server

test:~$ cd freeradius-server-3.0/

FreeRADIUS: Check the current working directory using pwd command

Note

  • Make sure your current working directory is freeradius-server-3.0

test:~$ pwd
/home/test/freeradius-server-3.0

FreeRADIUS: Open debian/rules and add this line –without-rml_sql_iodbc above –without-rlm_eap_ikev2

test:~$ vim debian/rules
--without-rml_sql_iodbc \
--without-rlm_eap_ikev2 \

FreeRADIUS: Configure for Compilation

test:~$ ./configure

FreeRADIUS: Build the Radius server

test:~$ make

FreeRADIUS: Go to raddb folder (all radius server/client files and certificates and keys will be generated here)

test:~$ cd /usr/local/etc/raddb

FreeRADIUS: Open clients.conf file and verify localhost client is present else add your own client like below

test:~$ sudo vi clients.conf

client 192.168.56.10{
ipaddr = 192.168.56.10
secret = testing123
}  

FreeRADIUS: Open users file and uncomment below two lines or add

test:~$ sudo vi users

bob 	Cleartext-Password := "testing123"
 	Reply-Message := "Hello, %{User-Name}"

FreeRADIUS: Set default_eap_type=tls in eap file located in /usr/local/etc/raddb/mods-enabled

test:~$ sudo vi /usr/local/etc/raddb/mods-enabled/eap

default_eap_type=ttls

FreeRADIUS: Start radius server

test:~$ sudo radiusd -X
  • Run AP mode operation with hostapd

AP : Download hostapd

Note

  • Make sure internet is available in laptop to download hostapd package

test:~$ wget http://w1.fi/releases/hostapd-2.9.tar.gz

AP: Install required packages

test:~$ sudo apt install libnl-genl-3-dev libnl-3-dev libdbus-glib-1-dev

AP : Extract hostapd

test:~$ tar -xzvf hostapd-2.9.tar.gz

AP : Change directory to hostapd

test:~$ cd hostapd-2.9/hostapd/

AP : Check the current working directory using pwd command

Note

  • Make sure your current working directory is hostapd

test:~$ pwd
/home/test/hostapd-2.9/hostapd

AP : Copy the contents of defconfig file to .config file

Note

  • .config file is required for make to start compilation of hostapd

test:~$ sudo cp defconfig .config

AP : Complile hostapd

Note

  • Compile hostapd by running make command

test:~$ make

AP : Check for the binaries created

Note

  • Make sure hostapd and hostapd_cli are present

test:~$ ls
hostapd
hostapd_cli

AP : Create a hostapd.conf file in /etc/hostapd folder with below content

test:~$ sudo vim /etc/hostapd/hostapd.conf

ctrl_interface=/var/run/hostapd
interface=enp0s8
driver=wired
logger_stdout=1
logger_stdout_level=1
debug=2
ieee8021x=1
eap_server=0
eap_user_file=/etc/hostapd/eap_user
eap_reauth_period=3600
use_pae_group_addr=1
auth_algs=1
auth_server_addr=127.0.0.1
auth_server_port=1812
auth_server_shared_secret=testing123
acct_server_addr=127.0.0.1
acct_server_port=1812
acct_server_shared_secret=testing123
macaddr_acl=0
ca_cert=/usr/local/etc/raddb/certs/ca.pem
server_cert=/usr/local/etc/raddb/certs/server.crt
private_key=/usr/local/etc/raddb/certs/server.p12
private_key_passwd=whatever 

AP : Create a file eap_user in /etc/hostapd/ folder with below content

test:~$ sudo vim /etc/hostapd/eap_user

AP : Run hostapd

test:~$ sudo ./hostapd /etc/hostapd/hostapd.conf
enp0s8: interface state UNINITIALIZED->ENABLED
enp0s8: AP-ENABLED

STA : Download wpa_supplicant

Note

  • Make sure internet is available in laptop to download supplicant package

test:~$ wget https://w1.fi/releases/wpa_supplicant-2.9.tar.gz

STA: Install required packages

test:~$ sudo apt install libnl-genl-3-dev libnl-3-dev libdbus-glib-1-dev

STA : Extract wpa_supplicant

test:~$ tar -xvf wpa_supplicant-2.9.tar.gz

STA : Change directory to wpa_supplicant

test:~$ cd wpa_supplicant-2.9/wpa_supplicant/

STA : Check the current working directory using pwd command

Note

  • Make sure your current working directory is wpa_supplicant

test:~$ pwd
/home/test/wpa_supplicant-2.9/wpa_supplicant

STA : Copy the contents of defconfig file to .config file

Note

  • .config file is required for make to start compilation of supplicant

test:~$ cp defconfig .config

STA : Compile wpa_supplicant

Note

  • Compile supplicant by running make command.

test:~$ make

STA: You might get errors while make regarding openssl headers in that case install the openssl headers and then do make clean and then do make again.

test:~$ sudo apt install libssl-dev
test:~$ make clean
test:~$ make

STA : Check for the binaries created

Note

  • Make sure wpa_supplicant and wpa_cli are present

test:~$ ls
wpa_supplicant
wpa_cli

STA: Copy required certificates from hostapd to wpa_supplicant

STA : Create wpa_supplicant.conf

test:~$ sudo vim wpa_supplicant.conf

ctrl_interface=/run/wpa_supplicant
update_config=1
network={
key_mgmt=WPA-EAP
eap=TTLS
phase2="auth=CHAP"
identity="bob"
password="testing123"
}

STA : Run wpa_supplicant

test:~$ sudo ./wpa_supplicant -D wired -i enp0s8 -c wpa_supplicant.conf
enp0s8: CTRL-EVENT-EAP-SUCCESS EAP authentication completed successfully

STA: Test

test:sudo ./wpa_cli -i enp0s8
> status
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