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CLI-based Configuration Guide - WLAN-AC

AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R010

This document provides the concepts, configuration procedures, and configuration examples of WLAN-AC features.
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Security Policy

Security Policy

Four WLAN security policies are available: Wired Equivalent Privacy (WEP), Wi-Fi Protected Access (WPA), WPA2, WLAN Authentication and Privacy Infrastructure (WAPI). Each security policy has a series of security mechanisms, including the link authentication mechanism used to establish a wireless link, user authentication mechanism used when users attempt to connect to a wireless network, and data encryption mechanism used during data transmission.

WEP

Wired Equivalent Privacy (WEP), defined in IEEE 802.11, is used to protect the data of authorized users from tampering during transmission on a WLAN. WEP uses the RC4 algorithm to encrypt data using a 64-bit, 128-bit encryption key. An encryption key contains a 24-bit initialization vector (IV) generated by the system, so the length of key configured on the WLAN server and client is 40-bit, 104-bit, or 128 bit. WEP uses a static encryption key. That is, all STAs associating with the same SSID use the same key to connect to the wireless network.

A WEP security policy defines a link authentication mechanism and a data encryption mechanism.

Link authentication mechanisms include open system authentication and shared key authentication. For details about link authentication, see "Link Authentication" in STA Access.

  • If open system authentication is used, data is not encrypted during link authentication. After a user goes online, service data can be encrypted by WEP or not, depending on the configuration.

  • If shared key authentication is used, the WLAN client and server complete key negotiation during link authentication. After a user goes online, service data is encrypted using the negotiated key.

WPA/WPA2

WEP shared key authentication uses the RC4 symmetric stream cipher to encrypt data. This authentication method requires the same static key pre-configured on the server and client. Both the encryption mechanism and encryption algorithm can bring security risks to the network.

The Wi-Fi Alliance developed Wi-Fi Protected Access (WPA) to overcome the shortcomings of WEP before more secure policies were provided in 802.11i. WPA still uses the RC4 algorithm, but it uses an 802.1X authentication framework and supports Extensible Authentication Protocol-Protected Extensible Authentication Protocol (EAP-PEAP) and EAP-Transport Layer Security (EAP-TLS) authentication, and defines the Temporal Key Integrity Protocol (TKIP) encryption algorithm.

Later, 802.11i defined WPA2. WPA2 uses Counter Mode with CBC-MAC Protocol (CCMP), a more secure encryption algorithm than those used in WPA.

Both WPA and WPA2 support 802.1X authentication and the TKIP/CCMP encryption algorithms, ensuring better compatibility. The two protocols provide almost the same security level and their difference lies in the protocol packet format.

The WPA/WPA2 security policy involves four steps:
  1. Link authentication
  2. Access authentication
  3. Key negotiation
  4. Data encryption
Link Authentication

Link authentication can be completed in open system authentication or shared key authentication mode. WPA and WPA2 support only open system authentication.For details, see "Link Authentication" in STA Access.

Access Authentication
WPA and WPA2 have an enterprise edition and a personal edition.
  • The WPA/WPA2 enterprise edition (WPA/WPA2-802.1X authentication) uses a RADIUS server and the EAP protocol for authentication. Users provide authentication information, including the user name and password, and are authenticated by an authentication server (generally a RADIUS server).

    Large-scale enterprise networks usually use the WPA/WPA2 enterprise edition.

    NOTE:

    For details about 802.1X authentication, see 802.1X Authentication in the Configuration Guide - Security.

    WPA/WPA2 implements 802.1X authentication using EAP-TLS and EAP-PEAP. Figure 7-4 and Figure 7-5 show the EAP-TLS 802.1X authentication and EAP-PEAP 802.1X authentication processes.

    Figure 7-4  EAP-TLS 802.1X authentication

    Figure 7-5  EAP-PEAP 802.1X authentication

  • WPA/WPA2 personal edition:

    A dedicated authentication server is expensive and difficult to maintain for small- and medium-scale enterprises and individual users. The WPA/WPA2 personal edition provides a simplified authentication mode: pre-shared key authentication (WPA/WPA2-PSK). This mode does not require a dedicated authentication server. Users only need to set a pre-shared key (PSK) on each WLAN node (including WLAN server, wireless router, and wireless network adapter).

    A WLAN client can access the WLAN if its pre-shared key is the same as that configured on the WLAN server. The PSK is not used for encryption; therefore, it does not pose security risks like the 802.11 shared key authentication.

802.1X authentication can be used to authenticate wireless and wired users, whereas PSK authentication is specific to wireless users.

PSK authentication requires that a STA and an AC be configured with the same PSK. The STA and AC authenticate each other through key negotiation. During key negotiation, the STA and AC use their PSKs to decrypt the message sent from each other. If the messages are successfully decrypted, the STA and AC have the same PSK. If they use the same PSK, PSK authentication is successful; otherwise, PSK authentication fails.

Key Negotiation

802.11i defines two key hierarchies: pairwise key hierarchy and group key hierarchy. The pairwise key hierarchy protects unicast data exchanged between STAs and APs. The group key hierarchy protects broadcast or multicast data exchanged between STAs and APs.

During key negotiation, a STA and an AC use the pairwise master key (PMK) to generate a pairwise transient key (PTK) and a group temporal key (GTK). The PTK is used to encrypt unicast packets, and the GTK is used to encrypt multicast and broadcast packets.

  • In 802.1X authentication, a PMK is generated in the process shown in Figure 7-4.

  • In PSK authentication, the method to generate a PMK varies according to the from of the PSK, which is configured using a command:
    • If the PSK is a hexadecimal numeral string, it is used as the PMK.
    • If the PSK is a character string, the PMK is calculated using a hash algorithm based on the PSK and service set identifier (SSID).

Key negotiation consists of unicast key negotiation and multicast key negotiation.

  • Unicast key negotiation

    Key negotiation is completed through a four-way handshake between a STA and an AC, during which the STA and AC send EAPOL-Key frames to exchange information, as shown in Figure 7-6.
    Figure 7-6  Unicast key negotiation

    The unicast key negotiation process consists of the following steps:

    1. The AC sends an EAPOL-Key frame with a random value (ANonce) to the STA.
    2. The STA calculates the PTK using its own MAC addresses and the MAC address of the AC, the PMK, ANonce, and SNonce, and sends an EAPOL-Key frame to the AC. The EAPOL-Key frame carries the SNonce, robust security network (RSN) information element, and message integrity code (MIC) of the EAPOL-Key frame. The AC calculates the PTK using the its own MAC addresses and the MAC address of the STA, the PMK, ANonce, and SNonce, and validates the MIC to determine whether STA's PMK is the same as its own PMK.
    3. The AC sends an EAPOL-Key frame to the STA to request the STA to install the PTK. The EAPOL-Key frame carries the ANonce, RSN information element, MIC, and encrypted GTK.
    4. The STA sends an EAPOL-Key frame to the AC to notify the AC that the PTK has been installed and will be used. The AC installs the PTK after receiving the EAPOL-Key frame.
  • Multicast key negotiation

    Multicast key negotiation is completed through a two-way handshake. The two-way handshake begins after the STA and AC generate and install a PTK through a four-way handshake. Figure 7-7 shows the two-way handshake process.
    Figure 7-7  Multicast key negotiation

    The multicast key negotiation process consists of the following steps:

    1. The AC calculates the GTK, uses the unicast key to encrypt the GTK, and sends an EAPOL-Key frame to the STA.
    2. After the STA receives the EAPOL-Key frame, it validates the MIC, decrypts the GTK, installs the GTK, and sends an EAPOL-Key ACK frame to the AC. After the AC receives the EAPOL-Key ACK frame, it validates the MIC and installs the GTK.
Data Encryption

WPA and WPA2 support the TKIP and CCMP encryption algorithms.

  • TKIP

    Unlike WEP, which uses a static shared key, TKIP uses a dynamic key negotiation and management mechanism. Each user obtains an independent key through dynamic negotiation. Each user obtains an independent key through dynamic negotiation. User keys are calculated using the PTK generated in key negotiation, the MAC address of the sender, and the packet sequence number.

    TKIP uses MICs to ensure the integrity of frames received on the receiver and validity of data sent by the sender and receiver. This mechanism protects information integrity. A MIC is calculated using the MIC key generated during key negotiation, the destination MAC address, source MAC address, and data frame.

  • CCMP

    While WEP and TKIP use a stream cipher algorithm, CCMP uses an Advanced Encryption Standard (AES) block cipher. The block cipher algorithm overcomes defects of the RC4 algorithm and provides a higher level of security.

WAPI

WLAN Authentication and Privacy Infrastructure (WAPI) is a Chinese national standard for WLANs, which was developed based on IEEE 802.11. WAPI provides higher security than both WEP and WPA and consists of the following:

  • WLAN Authentication Infrastructure (WAI): authenticates user identities and manages keys.
  • WLAN Privacy Infrastructure (WPI): protects data transmitted on WLANs and provides the encryption, data verification, and anti-replay functions.

WAPI uses the elliptic curve cryptography (ECC) algorithm, which is based on public key cryptography and the block key algorithm based on symmetric-key cryptography. The ECC algorithm is used for digital certificate authentication and key negotiation between wireless devices. The block key algorithm is used to encrypt and decrypt data transmitted between wireless devices. The two algorithms implement identity authentication, link authentication, access control, and user information encryption.

WAPI has the following features:
  • Bidirectional identity authentication

    Bidirectional identity authentication prevents access from unauthorized STAs and protects a WLAN against attacks from unauthorized WLAN devices.

  • Digital certificate as identity information

    A WAPI system has an independent certificate server. STAs and WLAN devices use digital certificates to prove their identities, improving network security. When a STA requests to join or leave a network, the administrator only needs to issue a certificate to the STA or revoke the certificate of the STA.

  • Well-developed authentication protocol

    WAPI uses digital certificates to identify STAs and wireless devices. During identity authentication, the elliptic curve digital signature algorithm is used to verify a digital certificate. In addition, the secure message hash algorithm is used to ensure message integrity, which prevents attackers from tampering or forging information transmitted during identity authentication.

WAPI involves identity authentication and key negotiation, which begin after a STA associates with an AC, as shown in Figure 7-8.

Figure 7-8  WAPI networking

Identity Authentication

WAPI provides two identity authentication modes: certificate-based mode (WAPI-CERT) and pre-shared key-based mode (WAPI-PSK).

  • WAPI-CERT: A STA and an AC authenticate each other's certificate. The certificates must be loaded on the STA and AC and verified by an authentication service unit (ASU). After certificate authentication is complete, the STA and AC use the temporal public key and private key to generate a base key (BK) for key negotiation.

    The WAPI-CERT mode is applicable to large-scale enterprise networks or carrier networks that can deploy and maintain an expensive certificate system.

    Figure 7-9 shows the WAPI certificate authentication process.

    Figure 7-9  WAPI certificate authentication

    The WAPI certificate authentication process is as follows:

    1. Authentication activation

      When a STA requests to associate or re-associate with an AC, the AC checks whether the user is a WAPI user. If the user is a WAPI user, the AC sends an authentication activation packet to trigger the certificate authentication process.

    2. Access authentication request

      The STA sends an access authentication request carrying the STA's certificate and the system time to the AC. The system time is the access authentication request time.

    3. Certificate authentication request

      When the AC receives the access authentication request, it records the access authentication request time and sends a certificate authentication request to the ASU. The certificate authentication request carries the STA's certificate, access authentication request time, the AC's certificate, and a signature generated using the AC's private key and the preceding information.

    4. Certificate authentication response

      When the ASU receives the certificate authentication request, it authenticates the AC's signature and certificate. If the AC's signature and certificate are invalid, the authentication fails. If they are valid, the ASU authenticates the STA's certificate.

      After the authentication is complete, the ASU constructs a certificate authentication response with the STA's certificate authentication result, AC's certificate authentication result, and a signature generated using the authentication results, and sends the certificate authentication response to the AC.

    5. Access authentication response

      When the AC receives the certificate authentication response, it checks the signature to obtain the STA's certificate authentication result, and controls access of the STA based on the certificate authentication result. The AC then forwards the certificate authentication response to the STA. The STA checks the signature generated by the ASU to obtain the AC's certificate authentication result, and determines whether to associate with the AC based on the result.

      If the certificate authentication succeeds, the AC accepts the access request. If the certificate authentication fails, the AC disassociates the STA from the network.

  • WAPI-PSK: The STA and AC have the same PSK configured before authentication. The PSK is converted into a BK during authentication.

    The WAPI-PSK mode does not require an expensive certificate system, so it is applicable to individual users or small-scale enterprise networks.

Key Negotiation

After the AC is authenticated by the ASU, the AC initiates key negotiation with the STA. Key negotiation consists of two stages: unicast key negotiation and multicast key negotiation.

  • Unicast key negotiation

    The STA and AC obtain a unicast encryption key and unicast integrity key through unicast key negotiation and uses these keys to ensure the security of unicast data exchanged between them.

    During unicast key negotiation, the STA and AC use the KD-HMAC-SHA256 algorithm to calculate a unicast session key (USK) based on the BK. In addition to the USK, the STA and AC also negotiate the encryption key and identity key used to generate the multicast key.

    Figure 7-10 shows the unicast key negotiation process.

    Figure 7-10  WAPI unicast key negotiation

    The unicast key negotiation process is as follows:

    1. Unicast key negotiation request

      After a BK is generated, the AC sends a unicast key negotiation request packet to the STA.

    2. Unicast key negotiation response

      After the STA receives the unicast key negotiation request packet, it performs the following steps:

      1. Checks whether this negotiation process is triggered to update the unicast key.
        • If so, the STA proceeds to step b.
        • If not, the STA proceeds to step c.
        NOTE:

        WAPI allows the STA to directly send a unicast key negotiation response to the AC to initiate a unicast key update.

      2. Checks whether the challenge of the AC is the same as the challenge that is obtained in last unicast key negotiation and saved locally. If the two challenges are different, the STA drops the unicast key negotiation request packet.
      3. Generates a random challenge, and then uses the KD-HMAC-SHA256 algorithm to calculate a USK and the AC's challenge used for the next unicast key negotiation based on the BK, the AC's challenge, and the STA's challenge.
      4. Uses the message authentication key and HMAC-SHA256 algorithm to calculate a message authentication code, and sends it to the AC with a unicast key negotiation response packet.
    3. Unicast key negotiation ACK

      After the AC receives the unicast key negotiation response packet, it performs the following steps:

      1. Checks whether the AC's challenge is correct. If the AC's challenge is incorrect, the AC drops the unicast key negotiation response packet.
      2. Uses the KD-HMAC-SHA256 algorithm to calculate a USK and the AC's challenge used for the next unicast key negotiation based on the BK, AC's challenge, STA's challenge. The AC then calculates the local message authentication code using the message authentication key and HMAC-SHA256 algorithm, and compares the local message authentication code with that in the received unicast key negotiation response packet. If the two message authentication codes are different, the AC drops the unicast key negotiation response packet.
      3. Checks the WAPI information element in the response packet if this is the first unicast key negotiation after the BK is generated. If the network type is BSS, the AC checks whether the WAPI information element in the response packet is the same as that in the association request packet it received before. If they are different, the AC sends a Deauthentication frame to disassociate the STA. If the network type is IBSS (ad-hoc network), the AC checks whether the unicast key algorithm supports the information element in the response packet. If not, the AC sends a Deauthentication frame to disassociate the STA.
      4. Uses the message authentication key and HMAC-SHA256 algorithm to calculate a message authentication code, and sends it to the STA with a unicast key negotiation ACK packet.
  • Multicast key negotiation

    Multicast key negotiation is performed after unicast key negotiation is complete. The AC advertises the multicast keys to the STA in this process.

    The AC uses the multicast encryption key and multicast integrity key derived from the multicast master key (MMK) to encrypt broadcast or multicast data it sends, and sends a multicast key advertisement packet to the STA. The STA obtains the multicast encryption key and multicast integrity key from the multicast key advertisement packet to decrypt the broadcast or multicast data it receives.

    Figure 7-11 shows the multicast key negotiation process.

    Figure 7-11  WAPI multicast key negotiation

    The multicast key negotiation process is as follows:

    1. Multicast key advertisement

      The AC uses the random number algorithm to calculate an MMK, encrypts the MMK using the negotiated unicast key, and sends an advertisement packet to notify the STA of the MMK.

    2. Multicast key response

      After the STA receives the multicast key advertisement packet, it performs the following steps:

      1. Calculates the checksum using the message authentication key identified by the unicast key identifier, and compares the checksum with the message authentication code. If the checksum is different from the message authentication code, the STA drops the multicast key advertisement packet.
      2. Checks whether the key advertisement identifier is increasing. If not, the STA drops the multicast key advertisement packet.
      3. Decrypts the multicast key to obtain the 16-byte master key and uses the KD-HMAC-SHA256 algorithm to extend it to 32 bytes. The first 16 bytes indicate the encryption key, and the last 16 bytes indicate the integrity key.
      4. Saves the key advertisement identifier and sends a multicast key response packet to the AC.
      5. After the AC receives the multicast key response packet, it performs the following steps:
        1. Calculates the checksum using the message authentication key identified by the unicast key identifier, and compares the checksum with the message authentication code. If the checksum is different from the message authentication code, the AC drops the multicast key response packet.
        2. Compares fields (such as key advertisement identifier) in the multicast key response packet with corresponding fields in the multicast key advertisement packet it has sent. If all the fields are the same, the multicast key negotiation is successful. Otherwise, the AC drops the multicast key response packet.
Key Update

WAPI features a dynamic key negotiation mechanism, but there may still be security risks if a STA uses the same encryption key for a long time. To enhance security, WAPI provides a time-based key update mechanism.

Time-based key update: The unicast and multicast keys of a STA have an aging time (configured using a command). When the aging time of the current unicast or multicast key expires, the STA and AC negotiate a new unicast or multicast key.

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Updated: 2019-05-20

Document ID: EDOC1100033726

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