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Voic 802.11e over phần 6

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OFDM là chặt chẽ liên quan đến đồng bằng cũ ghép kênh phân chia tần số (FDM). Cả haiCác đặc điểm kỹ thuật 802.11e dựa trên hơn một thập kỷ kinh nghiệm trong thiết kế của giao thức WLAN và được xây dựng từ mặt đất lên cho các điều kiện thực thế giới không dây. | Security and Vo802.11 125 actually knew its own secret key and thus could decrypt the ticket and the authenticator. Secure Communications The target server knows that the user is who he claims to be and the two now share an encryption key for secure communications. Because only the user and target server share this key they can assume that a recent message encrypted in that key originated with the other party. Disadvantages of Kerberos The Kerberos authentication system has an inherent disadvantage If an attacker logs on to the same computer at the same time as an authorized user the cached keys located on that computer are accessible to the attacker. The Kerberos system relies on the synchronization of the clocks located on the different machines. If an intruder can mislead a host in terms of the correct time the authentication ticket to the network can be used repeatedly as a result of the nonexpiring time stamp. Kerebos must trust that all three machines time authenticator servers KDC the client and the network server are void of an intruder. If a ticket is forwarded the system must trust all of the other systems that the ticket has traveled through before reaching the current server. However the server in which the ticket arrives cannot tell where it has come from it can only tell that it has been on other servers by a flag which has been set to 1. Passwords can be guessed by plugging a password guess into the public encryption key algorithm. The longer a ticket is granted the more likely it is to be stolen and used by an unauthorized user. In a wireless system using MAC address registration as an authentication method if the NIC is stolen the card has the inherent authentication of the user that is tied to that NIC and will be granted access to the network 18 . Standards Kerberos version 5 is standardized under RFC 1521 19 . Conclusion At the time of this writing there has been much coverage in the press regarding potential security holes in 802.11 security .