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21 networksecurity

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Unformatted text preview: Data and Computer Communications Communications Chapter 21 – Network Security Eighth Edition by William Stallings Lecture slides by Lawrie Brown Network Security Network To guard against the baneful influence exerted by strangers is therefore an elementary dictate of savage prudence. Hence before strangers are allowed to enter a district, or at least before they are permitted to mingle freely with the inhabitants, certain ceremonies are often performed by the natives of the country for the purpose of disarming the strangers of their magical powers, or of disinfecting, so to speak, the tainted atmosphere by which they are supposed to be surrounded. —The Golden Bough, Sir James George Frazer Security Requirements Security confidentiality - protect data content/access integrity - protect data accuracy availability - ensure timely service authenticity - protect data origin Passive Attacks Passive eavesdropping on transmissions to obtain information release of possibly sensitive/confidential release message contents message traffic analysis which monitors frequency and traffic length of messages to get info on senders length difficult to detect can be prevented using encryption Active Attacks Active masquerade pretending to be a different entity replay modification of messages denial of service easy to detect detection may lead to deterrent focus on detection and recovery hard to prevent Symmetric Encryption Symmetric Requirements for Security Requirements strong encryption algorithm even known, unable to decrypt without key even if many plaintexts & ciphertexts available sender and receiver must obtain secret sender key securely key once key is known, all communication once using this key is readable using Attacking Encryption Attacking cryptanalysis relay on nature of algorithm plus some knowledge of relay general characteristics of plaintext general attempt to deduce plaintext or key try every pos...
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