Describe the purpose and four typical functions of a root kit. [6 marks] 9 (TURN OVER) CST.2014.4.10 9

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- Security I Block ciphers usually process 64 or 128-bit blocks at a time. To illustrate how their modes of operation work, we can use instead a pseudo-random permutation that operates on the 26 letters of the English alphabet: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 m A B C D E F G H I J K L M N O P Q R S T U V W X Y Z EK(m) P K X C Y W R S E J U D G O Z A T N M V F H L I B Q As the XOR operation is not defined on the set {A, . . . , Z}, we replace it here during encryption with modulo-26 addition (e.g., C D = F and Y C = A). (a) Encrypt the plaintext "TRIPOS" using: (i) electronic codebook mode; [2 marks A new programming language has the notion of "statically scoped exceptions" in which the program exception foo; void f() { try { void g() { raise foo; } try { g(); } except (foo) { C2 } } except (foo) { C1 } } would execute C1 rather than C2 as the former was in scope at the raise point. By analogy with statically scoped variables, or otherwise, explain how such exceptions might be implemented on a stack. [10 marks] 6 CST.2004.13.7 7 Artificial Intelligence In the following, N is a feedforward neural network architecture taking a vector x T = ( x11 1x2 xn ) of n inputs. [4 marks] (f ) Consider different versions of an optimising compiler, each of which uses IEEE standard representation for all variables. Give two reasons why they might compile a floating-point program into code that, when run, produces differing results. [2 marks] The designer also wishes the real-time system to use demand paged virtual memory for efficiency. What problems could arise here, and how could they be overcome? [6 marks] 6 Numerical Analysis I (a) For Single Precision in the IEEE binary floating-point standard (IEEE 754) the precision is defined as 24, and the exponent requires 8 bits of storage. With reference to IEEE Single Precision, explain the terms exponent, significand, precision, sign bit, normalised number, denormal number. [6 marks] (b) Explain the term hidden bit. What are the values of the hidden bit for normalised and denormal numbers? How is the exponent stored and why? How are the exponent, significand and sign bit arranged in memory? [4 marks] The role of the C preprocessor in the source-code compilation cycle, and why it is a useful tool for debugging. [4 marks] (iii) Templated functions in C++, giving one benefit and one drawback of using them compared with using a void* function in C. 4. List the terminal images and non-terminal images, and count the creation rules both in the first syntax and in the sentence structure in your response to part (b). Demonstrate the beginning image in the two sentence structures. [2 marks] 5.Define a sort or types (in C, Java, or ML) appropriate for holding a theoretical Give a brief and rudimentary clarification of the standards of how the language coming about because of part (b) may be utilized to make a sentence structure analyser taking a token stream as information (by means of calls to work lex()) and giving as result an theoretical language structure tree relating to part (d). [13 marks] (f ) (a,87, 87c)