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Hacker Professional Ebook part 159

Tham khảo tài liệu 'hacker professional ebook part 159', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | c.d.f. In statistics cumulative distribution function. A function which gives the probability of obtaining a particular value or lower. CFB CFB or Ciphertext FeedBack is an operating mode for a block cipher. CFB is closely related to OFB and is intended to provide some of the characteristics of a stream cipher from a block cipher. CFB generally forms an autokey stream cipher. CFB is a way of using a block cipher to form a random number generator. The resulting pseudorandom confusion sequence can be combined with data as in the usual stream cipher. CFB assumes a shift register of the block cipher block size. An IV or initial value first fills the register and then is ciphered. Part of the result often just a single byte is used to cipher data and the resulting ciphertext is also shifted into the register. The new register value is ciphered producing another confusion value for use in stream ciphering. One disadvantage of this of course is the need for a full block-wide ciphering operation typically for each data byte ciphered. The advantage is the ability to cipher individual characters instead of requiring accumulation into a block before processing. Chain An operation repeated in a sequence such that each result depends upon the previous result or an initial value. One example is the CBC operating mode. Chaos The unexpected ability to find numerical relationships in physical processes formerly considered random. Typically these take the form of iterative applications of fairly simple computations. In a chaotic system even tiny changes in state eventually lead to major changes in state this is called sensitive dependence on initial conditions. It has been argued that every good computational random number generator is chaotic in this sense. In physics the state of an analog physical system cannot be fully measured which always leaves some remaining uncertainty to be magnified on subsequent steps. And in many cases a physical system may be slightly affected by .