tailieunhanh - A+ NETWORK+ SECURITY+ EXAMSIN A NUTSHELL phần 9

Hầu hết các mạng máy tính sử dụng công nghệ baseband. Các công nghệ băng thông rộng được sử dụng cho truyền hình cáp. Truy cập vào một máy chủ DHCP có thể cung cấp thông tin về một chương trình địa chỉ IP nội bộ. • DHCP server phải được bảo vệ hợp lý và lưu giữ đến ngày với các các bản vá lỗi bảo mật, các hotfix, và các gói dịch vụ. | Figures 11-9 and 11-10 show ad-hoc and infrastructure wireless network configurations respectively. Wired Equivalent Privacy WEP WEP is the primary security standard for wireless networks and it is designed to provide privacy in transmissions occurring between the AP and wireless client. It uses shared key authentication which allows encryption and decryption of wireless transmissions. Up to four different keys can be defined on the AP and the client and these keys can be rotated to enhance security. WEP encryption can use either 40- or 128-bit keys. When WEP is enabled on the AP and the wireless clients the encryption keys and the SSID must match on both ends. WEP is easy to implement because the administrator or the user can define the keys. WEP uses the CRC-32 checksum for data integrity and privacy is ensured with the RC4 encryption algorithm. RC4 is a stream cipher and both the AP and the client encrypt and decrypt messages using a known preshared key. The sender 644 Chapter 11 Security Exam Study Guide runs the plain text message through an integrity check algorithm Cyclic Redundancy Check CRC-32 to produce the Integrity Check Value ICV . The ICV is added to the plain text message. A random 24-bit Initialization Cector IC is generated and added to the beginning of the secret key to ensure the key s security. The ec is changed every time to prevent reuse of the key. Authentication in wireless networks The IEEE standard defines the following two types of authentication in wireless networks. Open authentication. Open authentication is device-specific and allows almost all devices access to the wireless network. It should not be assumed that the open authentication method does not use encryption because all devices are granted access. This method can also require the use of WEP keys. Any client who knows the SSID of the AP can connect to the wireless network. Shared key authentication. Shared key authentication is used to grant access only to those