Answer to Question #180401 in Programming & Computer Science for am1

Question

Q1. Upper case ASCII letters A to Z are represented by the denary numbers 65 to 90; lower case ASCII letters a to z are represented by the denary numbers 97 to 122. The decimal value is converted to 7-bit binary. To encrypt any letter its 7-bit binary value is combined with a 7-bit secret key using bitwise XOR. A 3-letter word has been encrypted one letter at a time. The encrypted word is OQv. If the secret key is 0111000 what was the original (plaintext) message? 

Q3. Use the RSA cipher to decrypt the word TfG. The public key is N=221, e=5. Decrypt a single letter at a time. You may use an Excel spreadsheet but for full marks you must explain each step of your calculation.

Q4. Alice's RSA public key [N:e] is stored in binary as [1111010011000111:00001011]. Eve wants to find Alice's private key by factorising N. (a) What are the factors of N and what is Alice's private key?

Answer 1

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