Answer to Question #251947 in C++ for Steve Jobs

Question

Lets create your first cipher!!! Cipher is an algorithm that you can use to encrypt and decrypt

sensitive information. In an information system, sensitive information is stored in a 16-bit unsigned

number, where bit-wise information is stored in following format, 9-bits are reserved for account number

and 7-bits are reserved for customer ID.

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

C C C C C C C A A A A A A A A A

a) Using bit wise operators, write a function to extract customer ID

b) Another function to extract account number.

c) Due to security concerns, you have been given a task to create a cipher. Write a function to

encrypt the 16-bit number (X) using the following expression.

y = aX + b, consider a = 5 and b = 233

d) Write another function to decrypt the number and display the original number.

Answer 1

#include <iostream>
#include <cstdint>
using namespace std;

uint16_t selectID(uint16_t x) {
    return (x & 0xFE00) >> 9;
}

uint16_t selectAccount(uint16_t x) {
    return (x & 0x01FF);
}

uint16_t encrypt(uint16_t x) {
    uint16_t a = 5, b = 233;
    return a*x + b;
}

uint16_t decrypt(uint16_t y) {
    uint16_t a = 5, b = 233;
    uint32_t x = y - b;

    for (uint16_t i=0; i<a; i++) {
        if ( x % a == 0 ) {
            break;
        }
        x += 0x10000;
    }
    return (uint16_t) (x/5);
}

int main() {
    uint16_t x = 0x1234;

    cout << "Customer ID is " << selectID(x) << endl;
    cout << "Customer account is " << selectAccount(x) << endl;

    for (uint16_t u = 100; u < 65000; u += 5000) {
        uint16_t e = encrypt(u);
        cout << "Encrypt of " << u << " is " << e << endl;
        cout << "Decrypt of " << e << " is " << decrypt(e) << endl << endl;
    }
}