ZyXEL MAX-306 User Guide - Page 281
Security Association, Diameter
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Appendix A WiMAX Security the network. In addition to the shared key, password information exchanged is also encrypted to protect the network from unauthorized access. Diameter Diameter (RFC 3588) is a type of AAA server that provides several improvements over RADIUS in efficiency, security, and support for roaming. Security Association The set of information about user authentication and data encryption between two computers is known as a security association (SA). In a WiMAX network, the process of security association has three stages. • Authorization request and reply The MS/SS presents its public certificate to the base station. The base station verifies the certificate and sends an authentication key (AK) to the MS/SS. • Key request and reply The MS/SS requests a transport encryption key (TEK) which the base station generates and encrypts using the authentication key. • Encrypted traffic The MS/SS decrypts the TEK (using the authentication key). Both stations can now securely encrypt and decrypt the data flow. CCMP All traffic in a WiMAX network is encrypted using CCMP (Counter Mode with Cipher Block Chaining Message Authentication Protocol). CCMP is based on the 128-bit Advanced Encryption Standard (AES) algorithm. 'Counter mode' refers to the encryption of each block of plain text with an arbitrary number, known as the counter. This number changes each time a block of plain text is encrypted. Counter mode avoids the security weakness of repeated identical blocks of encrypted text that makes encrypted data vulnerable to pattern-spotting. 'Cipher Block Chaining Message Authentication' (also known as CBC-MAC) ensures message integrity by encrypting each block of plain text in such a way that its encryption is dependent on the block before it. This series of 'chained' blocks creates a message authentication code (MAC or CMAC) that ensures the encrypted data has not been tampered with. User's Guide 281