Four-Way Handshake


A Four-Way Handshake is a security protocol used in the Wi-Fi Protected Access (WPA) and WPA2 wireless network standards to confirm the authenticity of devices and establish an encrypted connection. It consists of four messages exchanged between a client device and an access point, facilitating a shared encryption key called the Pairwise Transient Key (PTK). The process ensures secure data transmission, protection against replay attacks, and key updates for wireless clients.


The phonetic pronunciation of “Four-Way Handshake” is /fɔːr-weɪ ˈhændˌʃeɪk/.

Key Takeaways

  1. Four-Way Handshake is a crucial process in wireless security, primarily used in WPA and WPA2 authentication protocols to establish pairwise transient key (PTK) and confirm the authenticity of clients and access points.
  2. The handshake consists of four messages exchanged between the client (supplicant) and access point (authenticator); it provides data confidentiality, message integrity, and mutual authentication without requiring the clients to reveal their passwords to the access points.
  3. The process is vulnerable to attacks, such as disconnected clients losing their handshakes or offline dictionary attacks against weak passwords; the introduction of WPA3 and robust password policies has aimed to address these vulnerabilities and further enhance wireless security.


The Four-Way Handshake is a crucial element in wireless network security, specifically within the context of Wi-Fi Protected Access (WPA) and WPA2 protocols.

This term is important because it establishes a secure connection between a wireless access point (router) and a user’s device, ensuring confidentiality and integrity of data transmission.

During the handshake, the involved parties exchange cryptographic keys and confirm their identities, allowing the formation of a unique encryption key for that specific session.

This process effectively prevents unauthorized access and potential eavesdropping on the network, contributing to the overall security of Wi-Fi communications.


The Four-Way Handshake is a vital security feature designed to achieve secure communication and data transfer in wireless networks, particularly in the Wi-Fi Protected Access (WPA) and Wi-Fi Protected Access II (WPA2) protocols. The primary purpose of this mechanism is to ensure that both the access point (AP) and the client have a shared and valid encryption key, known as the Pairwise Transient Key (PTK), for secure communication.

By establishing a mutual understanding of the encryption key without revealing it, the Four-Way Handshake successfully maintains data confidentiality and safeguarding against potential eavesdroppers or third parties attempting unauthorized access. The process begins when a client device, such as a smartphone or laptop, tries to connect to a secure Wi-Fi network.

The Four-Way Handshake consists of a four-step exchange between the client and the AP, starting with the AP sharing an Anonce (a random number), followed by the client sharing its own Snonce (also a random number). Using these nonces and previously shared credentials (Pre-Shared Key or PSK and Authenticator Master Session Key or AMSK), both parties independently calculate and derive the PTK. Finally, the fourth message serves as a confirmation that the PTK is successfully installed, and communications can commence securely.

Ultimately, the Four-Way Handshake streamlines secure communication and is an integral component of wireless network security.

Examples of Four-Way Handshake

Wi-Fi Connection at Home: A four-way handshake is crucial for securely connecting devices to home Wi-Fi networks. When a device like a smartphone, tablet, or laptop tries to connect to the Wi-Fi router, the four-way handshake validates the device’s access to the network and directs the proper transfer of encryption keys, ensuring the network remains secure and the connection is reliable.

Office Networks: Similarly, office networks employ a four-way handshake to securely connect employees’ devices to the company’s Wi-Fi network. This technique ensures that sensitive company data doesn’t fall into the wrong hands due to unauthorized network access. It also helps manage access rights, authenticating the employee’s device as they interact with the network without compromising the company’s intellectual property.

Public Wi-Fi Hotspots: Public Wi-Fi hotspots, such as those found in airports, cafes, or libraries, depend on the four-way handshake to provide secure connections for their users. By utilizing this technology, the service provider can protect the session from unwanted access or interference, safeguarding users’ privacy and the integrity of the communication between the user’s device and the hotspot server.

Four-Way Handshake FAQ

What is a four-way handshake?

A four-way handshake is a process used in Wi-Fi Protected Access (WPA) and WPA2 protocols to establish a secure and encrypted connection between a client device and a wireless access point.

Why is it called a four-way handshake?

It is called a four-way handshake because there are four messages exchanged between the client device and the wireless access point during the process. These messages serve different purposes and ensure a secure connection.

What is the purpose of the four-way handshake?

The main purpose of the four-way handshake is to authenticate the client device and the wireless access point as well as to generate a unique encryption key, Pairwise Transient Key (PTK), for securing the communication between them.

How does the four-way handshake work?

The four-way handshake consists of the following steps:

  1. The access point sends a nonce value (ANonce) to the client device.
  2. The client device generates a nonce value (SNonce) and derives the PTK using the ANonce, SNonce, and shared secret key. The client sends the SNonce along with the Message Integrity Code (MIC) to the access point.
  3. The access point derives the PTK using the SNonce and sends the Group Temporal Key (GTK) along with the MIC to the client device.
  4. The client device verifies the MIC and installs the PTK and GTK. It sends an acknowledgment message to the access point, after which encrypted communication can begin.

Is the four-way handshake secure?

Yes, the four-way handshake is secure as long as the pre-shared key (PSK) or passphrase used is strong and is not compromised. The use of nonce values and MIC ensures that any tampering or replay attacks are detected and prevented.

What is the difference between WPA and WPA2 four-way handshake?

While the four-way handshake process remains the same for both WPA and WPA2, the main difference lies in the encryption protocol used. WPA uses Temporal Key Integrity Protocol (TKIP) for encryption, whereas WPA2 uses Advanced Encryption Standard (AES) which is more secure and faster than TKIP.

Related Technology Terms

  • Authentication
  • Encryption key
  • Wi-Fi Protected Access (WPA)
  • Temporal Key Integrity Protocol (TKIP)
  • IEEE 802.11i standard

Sources for More Information


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