Explain why public key encryption is more useful for securing communications on the Internet than private (shared) key encryption. 6. A certain CS professor gives 5-point quizzes that are graded on the scale 5-A, 4-B, 3-C, 2-D, 1-F, 0-F. Write a program that accepts a quiz score as an input and prints out the corresponding grade. 7. A certain CS professor gives 100-point exams that are graded on the scale 90-100:A, 80-89:B, 70- 79:C, 60-69:D, 60:F. Write a program that accepts an exam score as input and prints out the corresponding grade.

8. An acronym is a word formed by taking the first letters of the words in a phrase and making a word from them. For example, RAM is an acronym for "random access memory." Write a program that allows the user to type in a phrase and outputs the acronym for that phrase. Note: the acronym should be all uppercase, even if the words in the phrase are not capitalized. 9. Numerologists claim to be able to determine a person's character traits based on the "numeric value" of a name. The value of a name is determined by summing up the values of the letters of the name where 'a' is 1, 'b' is 2, 'c' is 3 etc., up to 'z' being 26. For example, the name "Zelle" would have the value 26 5 12 12 5 60 (which happens to be a very auspicious number, by the way). Write a program that calculates the numeric value of a single name provided as input. 10. Expand yoursolution to the previous problem to allow the calculation of a complete name such as "John Marvin Zelle" or "John Jacob Jingleheimer Smith." The total value is just the sum of the numeric value for each name. 11. A Caesar cipher is a simple substitution cipher based on the idea of shifting each letter of the plaintext message a fixed number (called the key) of positions in the alphabet. For example, if the key value is 2, the word "Sourpuss" would be encoded as "Uqwtrwuu." The original message can be recovered by "reencoding" it using the negative of the key. Write a program that can encode and decode Caesar ciphers. The input to the program will be a string of plaintext and the value of the key. The output will be an encoded message where each character in the original message is replaced by shifting it key characters in the ASCII character set. For example, if ch is a character in the string and key is the amount to shift, then the character that replaces ch can be calculated as: chr(ord(ch) + ke

A researcher notes that the message service, fritter, resembles a datagram service. It is prone to delivery delays of up to 1 second, message re-ordering and message loss. Fritter permits a 140-byte message to be relayed between any two users and each message is delivered without data-corruption. You are asked to implement a Stop-and-wait ARQ to provide a unidirectional reliable byte-stream delivery service between two fritter users. Assume this is the only service between the two fritter users. (i) Provide a labelled diagram illustrating the format for a fritter message that could be used by a reliable, byte-stream, delivery service. Justify your answer. [3 marks] (ii) Draw and label the Finite State Machine that implements the sender portion of the Stop-and-wait ARQ. Your function will be called as reliable send() while the fritter message receive and message send functions are fritter rcv() and fritter send() respectively. You may assume that the argument to the reliable send() function does not exceed 100 bytes per function call. [8 marks] (iii) Users assert that the performance using your Stop-and-wait ARQ is terrible for large transfers. Explain why they are correct. [2 marks] (iv) Describe an appropriate enhancement to the ARQ that will improve performance. Given the constraints of a small fritter message size, justify why your particular ARQ enhancement is best suited to the fritter application.

1 Write program that prints your full name.. Write program that prints your full name using asterisk(*). Write program that prints a square, a rectangle and a triangle using asterisk. 4

A Modula-3 library module is required to provide a buffered stream of characters between two threads, with appropriate synchronization. Write a Buffer interface defining an opaque object type, T, with the following methods: init: taking an argument specifying the buffer size and returning a suitably initialized object put: inserting a single character into the buffer get: extracting a single character from the buffer [4 marks] Sketch a corresponding implementation giving (a) the concrete revelation of the types [4 marks] (b) the three default methods [4 marks each]

24. Two variables store strings that consist of a letter of the alphabet, a blank space, and a number (in the form 'R 14.3). Write a script that would initialize two such variables. Then, use string manipulating functions to extract the numbers from the strings and add them together. Cryptography, or encryption, is the process of converting plaintext fe.g., a sentence or paragraph), into something that should be unintelligible, called the ciphertext. The reverse process is code-breaking, or cryptanalysis, which relies on searching the program encrypted message for weaknesses and deciphering it from that point. Modern security systems are heavily reliant on these processes.