112 lines
4.0 KiB
C
112 lines
4.0 KiB
C
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// cipher.h
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// Deitel implementation of the Vigen<65>re cipher.
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#pragma once
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#include <algorithm>
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#include <array>
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#include <iostream>
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#include <string>
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#include <cctype>
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#include <stdexcept>
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#include <gsl/gsl>
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class Cipher {
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public:
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Cipher() noexcept {
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std::array<char, size> alphabet{};
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for (int i{0}; i < size; ++i) {
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alphabet.at(i) = 'a' + i;
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}
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square.at(0) = alphabet;
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for (int row{1}; row < size; ++row) {
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std::rotate(alphabet.begin(), alphabet.begin() + 1, alphabet.end());
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square.at(row) = alphabet;
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}
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}
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std::string encrypt(const std::string& plainText,
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const std::string& secret) {
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checkKey(secret); // ensure only letters in secret
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std::string cipherText{};
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size_t keyCounter{0};
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for (size_t i{0}; i < plainText.length(); ++i) {
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const bool upper = std::isupper(plainText.at(i));
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const char current = std::tolower(plainText.at(i));
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if ('a' <= current && current <= 'z') {
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const int row{tolower(secret.at(keyCounter)) - 'a'};
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keyCounter = (keyCounter + 1) % secret.length();
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const int col{current - 'a'};
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const char substitute{square.at(row).at(col)};
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cipherText += (upper ? std::toupper(substitute) : substitute);
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}
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else {
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cipherText += plainText.at(i); // pass through numbers and punctuation
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}
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}
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return cipherText;
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}
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std::string decrypt(const std::string& text,
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const std::string& secret) {
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checkKey(secret); // ensure only letters in secret
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std::string plainText;
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size_t keyCounter{0};
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for (size_t i{0}; i < text.length(); ++i) {
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const bool upper = std::isupper(text.at(i));
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const char current = std::tolower(text.at(i));
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if ('a' <= current && current <= 'z') {
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const int row{std::tolower(secret.at(keyCounter)) - 'a'};
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keyCounter = (keyCounter + 1) % secret.length();
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int column{-1};
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for (size_t col{0}; col < square.at(row).size(); ++col) {
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if (square.at(row).at(col) == current) {
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column = gsl::narrow_cast<int>(col);
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break;
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}
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}
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const char original{gsl::narrow_cast<char>('a' + column)};
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plainText += (upper ? std::toupper(original) : original);
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}
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else {
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plainText += current; // pass through numbers and punctuation
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}
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}
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return plainText;
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}
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private:
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constexpr static int size{26};
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std::array<std::array<char, 26>, 26> square;
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// checks that secret key contains only letters
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void checkKey(std::string secret) {
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for (int i{0}; i < secret.size(); ++i) {
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if (tolower(secret.at(i)) < 'a' || tolower(secret.at(i)) > 'z') {
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throw std::invalid_argument(
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"key must contain only letters A-Z or a-z");
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}
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}
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}
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};
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/**************************************************************************
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* (C) Copyright 1992-2022 by Deitel & Associates, Inc. and *
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* Pearson Education, Inc. All Rights Reserved. *
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* *
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* DISCLAIMER: The authors and publisher of this book have used their *
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* best efforts in preparing the book. These efforts include the *
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* development, research, and testing of the theories and programs *
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* to determine their effectiveness. The authors and publisher make *
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* no warranty of any kind, expressed or implied, with regard to these *
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* programs or to the documentation contained in these books. The authors *
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* and publisher shall not be liable in any event for incidental or *
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* consequential damages in connection with, or arising out of, the *
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* furnishing, performance, or use of these programs. *
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**************************************************************************/
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