802.11 Frame Exchanges – Security #CWAP7

802.11 Frame Exchanges section account for 25% of syllabus for CWAP-403 exam. Potentially around 15 questions out of 60 in the exam can be expected from this section. This blog post focuses on the “security” component of 802.11 Frame Exchange. I will be focusing on other sections in the subsequent posts in the next week or two. Let’s begin!


1st step required to connect to 802.11 BSS. Both authentication and association must occur in order to successfully pass wireless traffic over to the AP and further. IEEE 802.11i-2004 defines RSNA. Open System & Shared Key Authentication are Prior to RSNA (Pre-RSNA) methods. The 802.11 authentication merely establishes an initial connection between the client and the access point, basically validating or authenticating that the STA is a valid 802.11 device.

  • Open System Authentication > Allows any device to authenticate and then attempt to communicate with the AP. The STA can communicate only its Wired Equivalent Privacy(WEP) keys match the AP
  • Shared Key Authentication > Not used anymore. Requires static WEP key configured on STA and AP.

Open System authentication and association between client STA and AP occurs prior to 802.1x/EAP authentication exchange between client STA and Radius server.

WLAN Encryption Methods

  • WEP
    • Pre-RSNA
    • Weak / Vulnerable / No Protection against replay attacks
    • Open/Shared Authentication
  • TKIP (Temporal Key Integrity Protocol) (RSN)
    • Uses dynamically created encryption keys as opposed to static keys.
    • 128-bit temporal key can either be a pairwise transient key (PTK) or group temporal key (GTK) used to encrypt
    • WPA-PSK & WPA-Enterprise
    • Can be vulnerable against certain attacks.
  • CTR with CBC-MAC Protocol (CCMP) (RSN)
    • CTR – Counter mode is used for data confidentiality
    • CBC MAC(Cipher-block chaining message authentication code) is used for integrity.
    • Used with AES block cipher suite with 128 bit key
  • SAE (Simultaneous Authentication of Equals)
    • Uses SAE known as Dragonfly Key Exchange, with forward secrecy feature
    • WPA3 Personal – 128 Bit SAE, Enterprise – 192 bit SAE
    • Not Vulnerable to KRACK attacks and offline dictionary attacks.

The info that is protected by these L2 encryption methods is data found in layers of 3-7. L2 encryption methods are used to provide data privacy for 802.11 data frames. These methods encrypt MSDU payload of an 802.11 data frame.

Security Protocols WEP TKIP (WPA) CCMP (WPA2) OWE (Opportunistic Wireless Encryption)
Cipher RC4 RC4 AES AES-GCM & Elliptical Curve Cryptography
Key 40/104 bits 128 bits 128 bits 192 bits
Authentication N/A IEEE 802.1X/EAP/PSK IEEE 802.1X/EAP/PSK WPA3 Personal / Enterprise
Data integrity CRC32 MIC CCMP Secure Hash Algorithm-2 for each input
IV Length 24 bits 48 bits 48 bits 24 bits

RSNA (Robust Security Network Association)
First published & ratified as IEEE 802.11i-2004, defined stronger encryption and better authentication methods. Now part of 802.11-2007 standard. Association between two stations is referred to as RSNA which means the two radios should share dynamic encryption keys that are unique between those two radios. CCMP/AES s mandatory, TKIP RC4 is optional. All client stations have to undergo a unique RSNA process called the 4-way handshake.

FIGURE 9.12 
Key 1 
RSNA within a BSS 
Group temporal key (GTK) 
Key 2 
Key 4 
Key 3 Access Point 
4-Way Handshake 
Keyl Key 4 
Key2 Key4 
Keys 1, 2, and 3 encrypt 
unicast traffic 
Key 4 encrypts 
broadcast/multicast traffic 
Key3 Key4

The RSN information element field is found in 4 management frames: beacon, probe, association request and reassociation request frames. Client STA use the association request frame & reassociation request (in case of roaming to/from) to inform the AP about their security capabilities.

FIGURE 9.18 
Client STA 
Client station RSN security capabilities 
Association request frame 
RSN information element: 
Client STA security capabilities 
1) CCMP/AES encryption 
2) 802.1X authentication 
Association response frame 
Success! - Welcome to the BSS! 
Access Point 
Original AP 
Roaming Client STA 
Reassociation request frame 
RSN information element: 
New AP 
Client STA security capabilities 
1) CCMP/AES encryption 
2) 802.1X authentication 
Reassociation response frame 
Success! - Welcome to the new BSS!

RSN information element – AES(CCMP) used in the below frame example.

v Tag: RSN Information 
Tag Number: RSN Information (48) 
Tag length: 20 
RSN Version: 1 
Group Cipher Suite: (leee 802.11) AES (CCM) 
Pairwise Cipher Suite Count: 1 
Pairwise Cipher Suite List (leee 802.11) AES (CCM) 
Auth Key Management (AOI) Suite Count: 1 
Auth Key Management (AKM) List (leee 802.11) WPA 
RSN Capabilities: 
— RSN Pre—Auth capabilities: Transmitter does not support pre—authentication 
0. — RSN No Pairwise capabilities: Transmitter can support WEP default key 0 simultaneously with Pairwise key 
10.. = RSN PTKSA Replay 
10 = RSN GTKSA Replay 
. 0.. = Management Frame 
= Management Frame 
= Joint Multi—band 
= PeerKey Enabled: 
Counter capabilities: 4 replay counters per PTKSA/GTKSA/STAKeySA (Ox2) 
Counter capabilities: 4 replay counters per PTKSA/GTKSA/STAKeySA (Ox2) 
Protection Required: False 
Protection Capable: False 
RSNA: False 


The 802.1X standard is port-based access control standard which provides an authorization framework that allows or disallows traffic to pass through port thereby granting access to the network resources.  802.1X can be implemented in either wireless/wired environments. The L2 protocol called EAP (Extensible Authentication Protocol) is used and consists of 3 major components of this framework.

  • Supplicant > Client STA
  • Authenticator > AP or WLAN Controller.
  • Authentication Server > Usually Radius(NPS), ISE (Cisco)
FIGURE 9.23 
comparison-autonomous access point and WLAN controller 
Autonomous AP 
Client station 
RADIUS server 
(authentication server) 
Network resources 
802. IX—Autonomous AP 
Client station 
WLAN controller 
RADIUS server 
(authentication server) 
Network resources 
802. IX—WLAN Controller


Defined in IETF RFC 2284 and ratified in the IETF RFC 3748, provides support to many authentication methods.

  • L2 Protocol
  • Two way authentication also called as mutual authentication.
  • EAP messages are encapsulated in EAP over LAN (EAPOL)
  • Five major types of EAPOL messages as shown below
TABLE 9.1 
Packet type 
0000 0000 
0000 0001 
0000 0010 
0000 0011 
0000 0100 
EAPOL messages 
EAPOL- Encapsulated - 
This is an encapsulated EAP frame. The majority 
of EAP frames are EAP-Packet frames. 
This is an optional frame that the supplicant 
can use to start the EAP process. 
This frame terminates an EAP session and 
shuts down the virtual ports. Hackers some- 
times use this frame for DOS attacks. 
This frame is used to exchange dynamic keying 
information. For example, it is used during the 
4-Way Handshake. 
This frame is used to send alerts, such as 
SNMP traps to the virtual ports.
FIGURE 9.27 
Generic EAP exchange 
1 802.11 association 
2 EAPoL-start 
4 EAP-response/identity (username) 
8 EAP-challenge-response 
Controlled and 
ports blocked 
Uncontrolled port opens 
Dynamic encryption keys created 
4-Way Handshake 
13 Controlled port opens

EAP Protocols

The stronger and more commonly deployed methods of EAP use TLS (Transport Layer Security) or TLS-tunneled authentication. EAP-MD5 and EAP-LEAP have only 1 supplicant identity making them weaker EAP types. EAP-TLS uses 2 supplicant identities – outer and inner identity. The outer identity is effectively a bogus username and can be seen clear text, and then inner identity is the true identity protected with TLS tunnel.  Table describes all the protocols with their characteristics.

802.1X EAP Types Feature / Benefit MD5 Message Digest 5 TLS Transport Level Security TTLS Tunneled Transport Level Security PEAP (WIDELY USED) Protected Transport Level Security FAST Flexible Authentication via Secure Tunneling LEAP Lightweight Extensible Authentication Protocol
Client-side certificate required no yes no no no (PAC) no
Server-side certificate required no yes yes yes no (PAC) no
WEP key management no yes yes yes yes yes
Rogue AP detection no no no no yes yes
Provider MS MS Funk Software MS Cisco Cisco
Authentication Attributes One way Mutual Mutual Mutual Mutual Mutual
Deployment Difficulty Easy Difficult (because of client certificate deployment) Moderate Moderate Moderate Moderate
Wi-Fi Security Poor Very High High High High High when strong passwords are used.

4-Way Handshake

802.11-2007 standard requires EAPOL-Key frames be used to exchange cryptographic information between STA supplicants and the authenticator, which is usually an AP. EAPOL key frames are used for the implementation of three different frames exchanges: 4-way handshake, group key exchange & peerkey handshake. 4 way handshake is the final process used to generate pairwise transient keys (PMK / GTK) for the encryption of unicast transmissions and the group temporal key for encryption of broadcast/multicast transmissions.

The 4-way handshake uses pseudorandom functions, it hashes various inputs to derive a value (PRF). The PMK is one of the inputs combined with other inputs to create the pairwise transient key (PMK). Some of the other inputs used by the PRF are called nonces. A nonce is a random numerical value that is generated one time only. In the case of 4-way handshake, a nonce is associated with the  PMK. Two nonces are created in 4-way handshake – authenticator nonce (anonce), supplicant nonce (snonce).

PTK = PRF (PMK + anonce + snonce + aa(Authenticator Mac)+ spa (Supplicant Mac).

M1 – Message 1

  • Authenticator sends EAPOL-Key frame containing “anonce” to supplicant
  • With this info,  supplicant have all the necessary input to generate PTK using PRF

M2 – Message 2

  • Supplicant sends an EAPOL-Key frame containing “snonce” to the authenticator
  • Authenticator has all the inputs to create PTK
  • Supplicant also sends RSN IE capabilities to Authenticator & MIC (message integrity code)

M3 – Message 3

  • If necessary, Authenticator will derive GTK from GMK
  • Authenticator sends EAPOL-key frame containing “anonce”, RSN-IE and a MIC.
  • GTP (encrypted with PTK) delivered to the supplicant.
  • Message to supplicant to install temporal keys.

M4 – Message 4

  • Supplicant sends final EAPOL-key frame to authenticator to confirm temporal keys have been installed.

Group Key Handshake

The 802.11-2007 standard also defines a two-frame handshake that is used to distribute a new group temporal key to client STA that have already obtained a PTK and GTK in a pervious 4-way handshake. The GKH is used only to issue a new group temporal key to client STA that have previously formed security associations. Effectively GKH is identical to M3/M4 in 4 way handshake.

Fast BSS Transition (FT)

Published in 2008, 802.11r – technical name for standardized fast secure roaming. An Amendment to improve handoff from one AP to another. The handoff is the same with or without 11r, the device is what ultimately decides when and where to roam.  802.11r are often discussed in context with WLAN controller architecture. Mobility domain is a group of AP that belong to the same ESS where the client STA can roam in a fast and secure manner. FT BSS transitions can happen over-the-air or over-the-DS (Distribution System).

FIGURE 9.33 
Fast BSS transition information element 
Element ID 

FT over-the-air (AP to AP, Same Controller)

  1. Client associates with AP1 and requests to roam to AP2
  2. Client sends a FT authentication request to AP2 and receive FT authentication response from AP2.
  3. Client sends FT reassociation request to AP2 and receives FT re-association response from AP2.
  4. Client completes the roaming from AP1 > AP2

FT over-the-air (AP-CONTROLLER|CONTROLLER-AP)(Inter-Controller)

  1. Step 1 & 2 similar to above steps.
  2. WLC1 ends PMK and mobility message to WLC-2 about the roaming client that uses mobility infrastructure.
  3. Client completes the roaming from AP1 > AP2
Tag: Mobility Domain 
Tag Number: Mobility Domain (54) 
Tag length: 3 
Mobility Domain Identifier: øxcd64 
FT Capability and Policy: exøø 
ø = Fast BSS Transition over DS: exø 
= Resource Request Protocol Capability: 
v Tag: Fast BSS Transition 
Tag Number: Fast BSS Transition (55) 
Tag length: 88 
MIC control: øxeeøø 
eøøø eøøø 
= Element Count: e 
MIC: eøøøooøøøøeeøøøeoøøøooøøøøooøøøe 
ANonce: øeoøøøøooøøøooøøøooøøøøooøøøooøøøooøøøøooøøøooøøm 
SNonce: cc1f8ga18b7615afa146b8249a7311283587dd66ca57eeeg„. 
Subelement ID: PMK—Rø key holder identifier (ROKH—ID) (3) 
Length: 4 
PMK-RO key holder identifier (ROKH-ID): cea814øa

FT over-the-DS (AP to AP, Same Controller)

  1. Client Associates to AP1 and requests to roam to AP2
  2. Client sends a FT authentication request to AP1 and receives a FT authentication response from AP1
  3. The controller sends the pre-authentication info to AP2 as the AP are member of same controller.
  4. Client sends a FT re-association request to AP2 and receives a FT re-association response from AP2.
  5. Client completes its roaming

FT over-the-DS (AP to AP, Different Controller)

  1. Step 1 and 2 are similar to above steps.
  2. WLC-1 sends PMK and mobility message to WLC-2 about the roaming client
  3. Client completes its roam from AP1 to AP2.
Tag: Mobility Domain 
Tag Number: Mobility Domain (54) 
Tag length: 3 
Mobility Domain Identifier: øxcd64 
FT Capability and Policy: Oxø1 
Fast BSS Transition over DS: Oxl 
Resource Request Protocol Capability: 
Tag: Fast BSS Transition 
Tag Number: Fast BSS Transition (55) 
Tag length: 88 
MIC control: øxeeøø 
eøøø eøøø 
= Element Count: e 
MIC: eøøøooøøøøooøøøooøøøooøøøøooøøøo 
ANonce: øeoøøøøooøøøooøøøooøøøøooøøøooøøøooøøøøooøøøooøø„. 
SNonce: f71ebøf1ef1b8725392f92f2979186ed912676cb6cb5cb53-. 
Length: 4 
PMK-RØ key 
ID: PM-Re key holder identifier (ROKH-ID) (3) 
holder identifier (ROKH—ID): cea814øa

Recommended Readings

FortiFocus – Virtual IPs

This section emphasizes on the Virtual IPs section in the FortiGate. I’ve learnt something which is not obvious behaviour and one of those ‘remind me later’ moments that I’ve encountered.

VIPs are essentially Destination Network Address Translation (DNAT) objects. For sessions matching the VIP, the destination address is translated. Let us go through some examples

In the above diagram, all connections going out from will use and not address.

Now, this is where it gets a bit tricky and deviate from default firewall behaviour. In the below firewall policy we would assume that no connections will be allowed to the LAN(internal_network) but VIPs can live up to their name (very important IP) and get users to access the web server even though the deny policy is at the top of the list.

SSL Inspection : Forti Focus

Often times we come across website which use certificates that not match the certificate of the site. It presents us with a warning message and option to proceed with risks, below image is quite common.

A number of applications and website that use SSL encryption correctly. In this case, the traffic goes through a Secure Sockets Layer (SSL) and is encrypted. However, there are risks associated with its use, since encrypted traffic can be used to around network. In common cases, users can unknowingly download a malicious file during an e-commerce session or there can be a phishing attachment sent with the secure email. Since the traffic is encrypted it can bypass the network’s security measures. To protect from the threat, SSL encryption can hold the key to unlock the sessions, examine the packets to find possible threats and blocks them.

When the deep inspection is used, the FortiGate impersonates the recipient of the originating SSL session, then decrypts and inspects the content. After successful inspection, it re-encrypts the content and creates a new session between FortiGate and recipient. A certificate is used from FortiGate’s own repository in order to re-encrypt the content.

There are 2 methods of deployment being used for SSL inspection.

Multiple clients connecting to multiple servers – This uses a CA certificate and applied to outbound policies destined to unknown servers or websites.

Protecting SSL server – Uses a server certificate, typically used for inbound policies

CWNA, Authentication & Encryption Types

Different Authentication types

  1. Open
  2. PSK
  3. 802.1X

Open Authentication – There is no authentication (Free for all). Device connects to wireless network without any issue.  Open Authentication might also redirect to a captive portal like at a Airport or Public Wireless places. There is a two way packet exchange. It is not the secure way to setup the wireless.

PSK / WPA/WPA2 – Preshared Key – Authentication using a set password on the network. Used in small/medium and mostly home deployments. Also deployed in secondary wireless network in organizations.
There is no additional requirements for authentication. PSK can be subjected to dictionary attacks. Suggested to change the PSK regularly. Recently there was an outbreak for WPA2 Krack attack (https://www.krackattacks.com/) You can setup a phrase or lengthy password. Consists of WPA/WPA2 Personal.

802.1X / WPA2 Enterprise – Strongest of all the authentication types. Framework which defines authentication, there is a Supplicant(Client which wants to connect), Authenticator(AP/Controller) and Authentication Server(Radius, ISE etc). Advantageous if there are more than 1 radius servers as a backup if primary server is not available due to any reason. Different EAP (Extensible Authentication Protocol) types are used in this setup. EAP method used (Credentials/Certificate/SIM Card etc) will be defined for the user authentication to the wireless network.

Upcoming Authentication Types in near future

SAE – Simultaneous Authentication of Equals – SAE is resistant to passive attack, active attack, and dictionary attack. It provides a secure alternative to using certificates or when a centralized authority is not available.
DPP – Device provisioning protocol – authenticate device without password like QR code, some kind of tag etc. Applies to lot of IoT devices which do not have screen for authentication.
WPA3 – The new WPA3 security standard is expected to land in devices later in 2019. our new capabilities for personal and enterprise Wi-Fi networks will emerge in 2018 as part of Wi-Fi CERTIFIED WPA3™. Two of the features will deliver robust protections even when users choose passwords that fall short of typical complexity recommendations, and will simplify the process of configuring security for devices that have limited or no display interface. Another feature will strengthen user privacy in open networks through individualized data encryption. Finally, a 192-bit security suite, aligned with the Commercial National Security Algorithm (CNSA) Suite from the Committee on National Security Systems, will further protect Wi-Fi networks with higher security requirements such as government, defense, and industrial. (https://www.wi-fi.org/news-events/newsroom/wi-fi-alliance-introduces-security-enhancements)

Encryption Types

Only the payload of data frames are encrypted in general cases. In some advanced cases, management frames can also be encrypted. Encryption here is targeted towards data frames.

None – No Encryption – Open Authentication, relying on application for encryption, not reliable. Suggested to use your personal VPN services to mitigate against any attacks. OWE – (Opportunistic Wireless Encryption) – may offer some encryption for open authentication in the near future. (https://tools.ietf.org/html/draft-wkumari-owe-00) 
TKIP (Temporal Key Integrity Protocol)- Introduced in 2002, Patch WEP (Wireless Encryption Protocol). It uses RC4 as its cipher, same as WEP.  You should refrain from using TKIP and upgrade your devices. Data rates are also limited to 54Mbps.
CCMP/AES (Counter Mode Cipher Block Chaining Message Authentication Code Protocol) – Strongest of all, not compromised till now. Suggested to use for your network. WPA/WPA2 – WPA uses TKIP, WPA2 uses CCMP/AES and TKIP as well.

Thanks to SemFio network for the diagram below.

CWNA , IEEE 802.11!

  • Hi IEEE 802.11 Key Concepts

Let’s get started with the IEEE 802.11 Journey synopsis. Standards are defined at physical and mac-sub layer(data-link). We are referring to different ways of transmitting data over the air. Also how our communication signal would deliver information. One of the original ones we’ve come across is FHSS (Frequency Hopping Spread Spectrum) and DSSS (Distributed Sequence Spread Spectrum).

In 2007, the IEEE consolidated 8 ratified amendments along with the original standard, creating a single document that was published as the IEEE standard 802.11-2007
The standard covers IEEE standard 802.11-1999, 802.11a.1999, 802.11b-1999, 802.11g-2003,802.11i-2004

802.11b (Sep 1999) is high rate DSSS – Based on 2.4GHz to 2.4835 GHz ISM band
802.11a (Sep 1999) is OFDM (Orthogonal Frequency Divisional Multiplexing) would operate in 5GHz frequency.  There are 3 U-NIII (Unlicensed National Information Infrastructure) frequency bands consisting of 12 channels.
802.11b (1999) – High Rate DSSS, operates in 2.4 GHz frequency. OFDM transmission type and supports BPSK (binary phase shift keying) and QPSK (Quadrature PSK) – 1 & 5.5Mbps and 2 & 11 Mbps. 
802.11g (June 2003) – Speeds upto 54Mbps/works similar to 802.11b in 2.4 GHz. Used a new technology called Extended Rate Physical (ERP) – ISM frequency band.
802.11i (Security) – From 1997 – 2004, not much defined in terms of security in the original 802.11 standard. Three key components of security solution – Data Privacy/Data Integrity/Authentication. This amendment defined a RSN (Robust Security Network).
802.11r-2008 (FT)-  Technology is more often referred to as fast secure roaming because it defines faster handoffs when roaming occurs between cells in WLAN using a strong security defined by RSN.
802.11w (Sep 2009) – IEEE Task Group was a way of delivering management frames in a security manner. Preventing the management frames from being able to be spoofed.802.11 – only on 2.4. Uses hi rate DSSS. It actually came out before 802.11a. Enabled 5.5 and 11Mbps data rates. 22MHz wide channels. Today these rates have become legacy rates. 
802.11n (October 2009) – also known as Wi-Fi 4 is an amendment that improves upon the previous 802.11 standards by adding multiple-input multiple-output antennas (MIMO). 802.11n operates on both the 2.4 GHz and the 5 GHz bands. Support for 5 GHz bands is optional. Its net data rate ranges from 54 Mbit/s to 600 Mbit/s
802.11ac (December 2013) – VTH (Very high throughput, wider channel (20MHz-160MHz) – also known as Wi-Fi 5 is an amendment to IEEE 802.11, published in December 2013, that builds on 802.11n.[28] Changes compared to 802.11n include wider channels (80 or 160 MHz versus 40 MHz) in the 5 GHz band, more spatial streams (up to eight versus four), higher-order modulation (up to 256-QAM vs. 64-QAM), and the addition of Multi-user MIMO (MU-MIMO). As of October 2013, high-end implementations support 80 MHz channels, three spatial streams, and 256-QAM, yielding a data rate of up to 433.3 Mbit/s per spatial stream, 1300 Mbit/s total, in 80 MHz channels in the 5 GHz band
802.11ax ( Sometime in 2019*)  – IEEE 802.11ax also known as Wi-Fi 6 is the successor to 802.11ac, and will increase the efficiency of WLAN networks. Currently in development, this project has the goal of providing 4x the throughput of 802.11ac at the user layer, having just 37% higher nominal data rates at the PHY layer.  More can be read here

While learning about 802.11 PHYs (Physical) I have come across this extremely useful table from cleartosend podcasts/posts as below




CWNA : New Things Learnt today

Cinemas jamming mobile phone signals #cinemajammers

The US’s National Association of Theater Owners wants the FCC’s permission to block mobile reception inside cinemas. To be honest I thought this already happened in some places… maybe I’d mentally linked it to office buildings with Faraday cage wall structures to prevent eavesdropping on wireless data transfer; I don’t know how common these are in general, but would guess that more sensitive workplaces have had these for a long time.
Of course, the problem with not being able to dial emergency services may be significant, although one would hope that the cinema staff would be able to use a land line to do that if alerted. What might be a more worrying problem is the audience not being able to receive messages/calls–imagine a situation where some urgent or critical news (e.g. “Come home, your house is on fire”) can’t be communicated to someone simply because he or she is in the cinema. Yes, before cellular phones (and pagers) that wouldn’t have been an issue anyway, but it is now.

#EVILTWIN #securityattack – Evil Twin attack

“A Fake WiFi access point is a wireless access point that has been installed on a secure network without explicit authorization from a local network administrator, whether added by a well-meaning employee or by a malicious attacker.” – Wikipedia

Fake WiFi access point is often called as:

Using this method it is possible to retrieve the WPA/2 passphrase in clear-text within minutes. No need of cracking or any extra hardware other than a Wireless adapter.

In some cases you don’t even need an adapter. When ? that we will discuss

Keep reading…


#fresnelzone  FRESNEL ZONE

resnel zones are used by propagation theory to calculate reflections and diffraction loss between a transmitter and receiver. Fresnel zones are numbered and are called ‘F1’, ‘F2’, ‘F3’ etc.

There are an infinite number of Fresnel zones, however, only the first 3 have any real effect on radio propagation.

In Radio Mobile Fresnel zones ove a radio path can be analysed in ‘Radio Link‘ and ‘RMpath

What is a Fresnel zone and why is it important?

Fist, what is it? A Fresnel zone is a cylindrical ellipse drawn between transmitter and receiver. The size of the ellipse is determined by the frequency of operation and the distance between the two sites.

Earth Bulge #Earthbulge

Earth bulge is a term used in telecommunications. It refers to the circular segment of earth profile which blocks off long distance communications.

Fade Margin #fademargin

Fade Margin is an expression for how much margin – in dB – there is between the received signal strength level and the receiver sensitivity of the radio.

4 Way Handshake



In my own simple words  4-way handshake between a client and an access point

Acronyms used:

PMK - pairwise master key
PRF = Pseudo Random Function
AA = Authenticator Address, SA = Supplicant Address
PTK = PRF(PMK | ANonce | SNonce | AA | SA)
MIC = Message integrity code
GTK = Group temporal key 
  1. EAP-Key Message 1/4 (ANonce) – AP to CLIENT
    As the first message is send from AP to client, this message includes a random number as ANonce for PTK generation at the client. Since the client knows its own SNonce and SA as well as the AA (from Beacons, Probe Response and/or Association Response) and PMK, the ANonce from this message is the only missing information.
  2. EAP-Key Message 2/4 – CLIENT to AP (SNonce, MIC)
    As the Supplicant (client) replies to the first EAP Key message, the client sends the used SNonce as clear text to the AP “protected” by a cryptographic hash (HMAC-SHA1) called Message Integrity Code (MIC) for integrity of of this message the installed key on the client side. The AP will generate its own MIC and compare it the the one in this message, if they match, EAP-Key message 3 is send for key installation. This message also includes the Robust Security Network Information Element (RSN IE).
  3. EAP-Key Message 3/4 – AP to CLIENT >

    Message 3 is the last unencrypted key message, as long as no retransmission(s) occur and the pairwise temporal key remains valid. The AP informs the client about the installation of the PTK and the receive sequence counter (RSC) for the GTK. The GTK itself is given in the WPA Key Data field, secured/encrypted with the PTK.

  4. EAP-Key Message 4/4 CLIENT to AP

    The Supplicant acknowledges the installation of PTK and GTK afterwards, encrypted Unicast and Broad-/Multicast transmission can start now.

NOTE: The 4 Way Handshake happens after the open system auth or 802.11 association. WPA/2 right after the association. In case of 802.1x it happens after above process in the image.


Duo MFA Security

Learnt something new today for DUO security. Any app or device can now be configured for MFA. Today i was able to get office 365 and azure login to redirect to DUO, got it working in less than 15 minutes. Quite amazing. Not sure if its so easy to configure or i am getting good at it 🙂 I am sure it is easy.

Followed this Microsoft blogpost to configure MFA with DUO – https://blogs.technet.microsoft.com/cbernier/2017/10/16/azure-ad-3rd-party-mfa-azure-ad-custom-controls/

#Duo #Security #MFA #2FA