计算机导论课件（北航）NP2014_Chapter05.pptVIP

* * Figure 5-20 – 5-21 * * * * Figure 5-25 * Figure 5-26 * * Figure 5-29 * Figure 5-30 * Figure 5-31 * Figure 5-32 * Figure 5-33 – 5-34 * Figure 5-36 * Figure 5-37 * Figure 5-38 * Figure 5-39 * * * * Figure 5-40 * Figure 5-41 * Figure 5-42 * Figure 5-45 * * Figure 5-47 * * * Figure 5-50 Figure 5-51 * Figure 5-52 * Encryption Encryption transforms a message so that its contents are hidden from unauthorized readers Plaintext has not yet been encrypted An encrypted message is referred to as ciphertext Decryption is the opposite of encryption Cryptographic algorithm Cryptographic key Chapter 5: Local Area Networks * Encryption Weak vs. strong encryption AES (Advanced Encryption Standard) Encryption methods can be broken by the use of expensive, specialized, code-breaking computers Chapter 5: Local Area Networks * Encryption Public key encryption (PKE) eliminates key-distribution problem, by using one key to encrypt a message and another key to decrypt the message Chapter 5: Local Area Networks * Encryption When personal computer users want to encrypt e-mail or other documents, they turn to public key encryption software such as PGP (Pretty Good Privacy), GnuPG, or AxCrypt Chapter 5: Local Area Networks * Question How can you tell if someone is hacking your network? A. Assign an IP address to each network device. B. Scan your router for viruses that might have been left by hackers. C. Set up your router software to maintain a log of network activity. D. Disable the SSID. Chapter 5: Local Area Networks * Answer C Chapter 5: Local Area Networks * FastPoll True/False QuestionsAnswer A for True and B for False (1) The networks typically installed by individuals in homes are classified as LANs. (2) High bandwidth networks, such as cable TV and DSL are referred to as broadband. (3) When you send an e-mail message over a network, it is chopped up into packets. (4) The IP address assigned to your computer on the