Cisco 7925G Administration Guide - Page 48

Security for Voice Communications in WLANs Chapter 2 Overview of the VoIP Wireless Network Authenticated Key Management The following authentication schemes use the RADIUS server to manage authentication keys: • WPA-Uses information on a RADIUS server to generate unique keys for authentication. Because these keys are generated at the centralized RADIUS server, WPA provides more security than WPA pre-shared keys that are stored on the AP and phone. • Cisco Centralized Key Management (CCKM)-Uses information on a RADIUS server and a wireless domain server (WDS) to manage and authenticate keys. The WDS creates a cache of security credentials for CCKM-enabled client devices for fast and secure reauthentication. With WPA and CCKM, encryption keys are not entered on the phone, but are automatically derived between the AP and phone. But the EAP username and password that are used for authentication must be entered on each phone. Encryption Methods To ensure that voice traffic is secure, the Cisco Unified Wireless IP Phone 7925G supports WEP, TKIP, and Advanced Encryption Standards (AES) for encryption. When using these mechanisms for encryption, both the signaling Skinny Client Control Protocol (SCCP) packets and voice Real-Time Transport Protocol (RTP) packets are encrypted between the AP and the wireless IP phone. • WEP-When using WEP in the wireless network, authentication happens at the AP by using open or shared-key authentication. The WEP key that is setup on the phone must match the WEP key that is configured at the AP for successful connections. The Cisco Unified Wireless IP Phone 7925G supports WEP keys that use 40-bit encryption or a 128-bit encryption and remain static on the phone and AP. EAP and CCKM authentication can use WEP keys for encryption. The RADIUS server manages the WEP key and passes a unique key to the AP after authentication for encrypting all voice packets; consequently, these WEP keys can change with each authentication. • TKIP-WPA and CCKM use TKIP encryption that has several improvements over WEP. TKIP provides per-packet key ciphering and longer initialization vectors (IVs) that strengthen encryption. In addition, a message integrity check (MIC) ensures that encrypted packets are not being altered. TKIP removes the predictability of WEP that helps intruders decipher the WEP key. • AES-An encryption method used for WPA2 authentication. This national standard for encryption uses a symmetrical algorithm that has the same key for encryption and decryption. AES uses Cipher Blocking Chain (CBC) encryption of 128 bits in size, supporting key sizes of 128, 192 and 256 bits, as a minimum. Note The Cisco Unified Wireless IP Phone 7925G does not support Cisco Key Integrity Protocol (CKIP) with CMIC. Choosing AP Authentication and Encryption Methods Authentication and encryption schemes are setup within the wireless LAN. VLANS are configured in the network and on the APs and specify different combinations of authentication and encryption. An SSID is associated with a VLAN and its particular authentication and encryption scheme. In order for wireless client devices to authenticate successfully, you must configure the same SSIDs with their authentication and encryption schemes on the APs and on the wireless IP phone. 2-18 Cisco Unified Wireless IP Phone 7925G Administration Guide for Cisco Unified Communications Manager 7.0(1) OL-15984-01