EAP-TTLS-EAP-GTC

What is Expansion of EAP-TTLS-EAP-GTC?

EAP-TTLS-EAP-GTC stands for Extensible Authentication Protocol - Tunneled Transport Layer Security - Extensible Authentication Protocol - Generic Token Card.

What is EAP-TTLS-EAP-GTC?

It is an authentication protocol combining EAP-TTLS (which provides a secure TLS tunnel) with EAP-GTC as the inner authentication method. EAP-GTC allows transmission of arbitrary text-based tokens such as one-time passwords or challenge-response data inside the secure tunnel.

Why is EAP-TTLS-EAP-GTC useful?

  • Enables secure authentication using token cards or password tokens without exposing credentials over the network.

  • Supports legacy authentication methods securely by tunneling inside TLS.

  • Useful when client certificates are not deployed.

  • Flexible and extensible for various authentication tokens.

How it works?

  1. TLS tunnel is established between the client and authentication server.

  2. Inside the tunnel, the server challenges the client using EAP-GTC.

  3. Client responds with the token (e.g., password, OTP).

  4. Server verifies and authenticates the client.

  5. Upon success, keys are generated for the secure session.

Where is EAP-TTLS-EAP-GTC used?

  • Wireless enterprise networks.

  • VPNs requiring token-based authentication.

  • Environments needing flexible inner authentication methods with secure tunneling.

Which OSI layer does this protocol belong to?

  • Application Layer (Layer 7).

IS EAP-TTLS-EAP-GTC windows specific?

  • No, it is platform independent.

  • Support varies depending on supplicant implementations.

IS EAP-TTLS-EAP-GTC Linux Specific?

  • No, supported by Linux supplicants like wpa_supplicant.

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

  • EAP over LAN (EAPOL) at Layer 2.

  • RADIUS (UDP) between authenticator and authentication server.

Which Port is used by EAP-TTLS-EAP-GTC?

  • UDP port 1812 (RADIUS Authentication).

Is EAP-TTLS-EAP-GTC using Client server model?

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

Whether EAP-TTLS-EAP-GTC protocol uses certificates?

  • Server certificates are mandatory to establish the TLS tunnel.

  • Client certificates are typically not required.

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

  • Multiple EAPOL frames for TLS handshake and inner EAP-GTC authentication.

  • Typically dozens of frames during full authentication.

Whether EAP-TTLS-EAP-GTC Protocol uses client certificates?

  • Generally no, authentication relies on tokens inside the tunnel.

Whether EAP-TTLS-EAP-GTC Protocol uses Server Certificates?

  • Yes, required for TLS tunnel establishment.

IS EAP-TTLS-EAP-GTC Protocol depends on TCP?

  • Not directly; the EAP and EAPOL operate at lower layers.

  • RADIUS typically uses UDP.

IS EAP-TTLS-EAP-GTC Protocol depends on UDP?

  • Yes, RADIUS messages are transported via UDP.

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

  • Client/Supplicant.

  • Authenticator (Access Point).

  • Authentication Server (e.g., FreeRADIUS).

  • Network analysis tools for capturing packets.

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

  • Yes, FreeRADIUS supports EAP-TTLS with inner EAP-GTC.

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

  • Limited support; external RADIUS servers like FreeRADIUS are preferred.

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

  • EAP-TTLS: RFC 5281.

  • EAP-GTC: RFC 3748 (EAP base), GTC defined in various drafts.

During Connection Procedure which EPoL Packets are encrypted?

  • Inner authentication messages (EAP-GTC token exchanges) are encrypted.

  • TLS handshake messages start unencrypted but establish tunnel security.

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

  1. Establish TLS tunnel between client and server.

  2. Inside the tunnel, perform EAP-GTC challenge/response token authentication.

  3. Server validates tokens and confirms authentication.

  4. Generate PMK for securing wireless session.

What is the final output of Connection Procedure?

  • Authentication success/failure status.

  • Pairwise Master Key (PMK) for securing wireless traffic.

  • Network access granted upon success.

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

  • 256-bit Pairwise Master Key (PMK).

Where the use of PMK generated by the Connection Procedure?

  • Used in the 4-way handshake to derive temporal encryption keys.

  • Secures subsequent wireless communication between client and AP.

  • 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="autheap=GTC"
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
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