11/* *
22 * @file vigenere_cipher.cpp
3- * @brief Implementation of [Vigenère
4- * cipher](https://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher) algorithm.
3+ * @brief Implementation of [Vigenère cipher](https://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher) algorithm.
54 *
65 * @details
7- * The Vigenère cipher is a method of encrypting alphabetic text by using a
8- * series of interwoven vigenere ciphers, based on the letters of a keyword. It
9- * employs a form of polyalphabetic substitution.
6+ * The Vigenère cipher is a method of encrypting alphabetic text by using a series of interwoven vigenere
7+ * ciphers, based on the letters of a keyword. It employs a form of polyalphabetic substitution.
108 *
119 * ### Algorithm
12- * The encryption can also be represented using modular arithmetic by first
13- * transforming the letters into numbers, according to the scheme, A → 0, B → 1,
14- * ..., Z → 25. Encryption of \f$i^{th}\f$ character in Message M by key K can
15- * be described mathematically as,
16- *
10+ * The encryption can also be represented using modular arithmetic by first transforming
11+ * the letters into numbers, according to the scheme, A → 0, B → 1, ..., Z → 25.
12+ * Encryption of \f$i^{th}\f$ character in Message M by key K can be described mathematically as,
13+ *
1714 * \f[ E_{K}(M_{i}) = (M_{i} + K_{i})\;\mbox{mod}\; 26\f]
18- *
19- * while decryption of \f$i^{th}\f$ character in Cipher C by key K can be
20- * described mathematically as,
15+ *
16+ * while decryption of \f$i^{th}\f$ character in Cipher C by key K can be described mathematically as,
2117 *
2218 * \f[ D_{k}(C_{i}) = (C_{i} - K_{i} + 26)\;\mbox{mod}\; 26\f]
23- *
24- * Where \f$K_{i}\f$ denotes corresponding character in key. If \f$|key| <
25- * |text|\f$ than same key is repeated untill their lengths are equal.
26- *
19+ *
20+ * Where \f$K_{i}\f$ denotes corresponding character in key. If \f$|key| < |text|\f$ than
21+ * same key is repeated untill their lengths are equal.
22+ *
2723 * For Example,
2824 * If M = "ATTACKATDAWN" and K = "LEMON" than K becomes "LEMONLEMONLE".
29- *
30- * \note Rather than creating new key of equal length this program does this by
31- * using modular index for key (i.e. \f$(j + 1) \;\mbox{mod}\; |\mbox{key}|\f$)
32- *
33- * \note This program implements Vigenère cipher for only uppercase English
34- * alphabet characters (i.e. A-Z).
35- *
25+ *
26+ * \note Rather than creating new key of equal length this program does this by using modular index for key
27+ * (i.e. \f$(j + 1) \;\mbox{mod}\; |\mbox{key}|\f$)
28+ *
29+ * \note This program implements Vigenère cipher for only uppercase English alphabet characters (i.e. A-Z).
30+ *
3631 * @author [Deep Raval](https://github.com/imdeep2905)
3732 */
38- #include < cassert> // for assert
39- #include < cstddef> // for size_t
40- #include < iostream> // for basic_ostream, operator<<, cout, endl
41- #include < string> // for basic_string, char_traits, string, operator<<
33+ #include < iostream>
34+ #include < string>
35+ #include < cassert>
4236
4337/* * \namespace ciphers
4438 * \brief Algorithms for encryption and decryption
4539 */
4640namespace ciphers {
47- /* * \namespace vigenere
48- * \brief Functions for [vigenère
49- * cipher](https://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher) algorithm.
50- */
51- namespace vigenere {
52- namespace {
53- /* *
54- * This function finds character for given value (i.e.A-Z)
55- * @param x value for which we want character
56- * @return corresponding character for perticular value
57- */
58- inline char get_char (const int x) {
59- // By adding 65 we are scaling 0-25 to 65-90.
60- // Which are in fact ASCII values of A-Z.
61- return char (x + 65 );
62- }
63- /* *
64- * This function finds value for given character (i.e.0-25)
65- * @param c character for which we want value
66- * @return returns corresponding value for perticular character
67- */
68- inline int get_value (const char c) {
69- // A-Z have ASCII values in range 65-90.
70- // Hence subtracting 65 will scale them to 0-25.
71- return int (c - 65 );
72- }
73- } // Unnamed namespace
74- /* *
75- * Encrypt given text using vigenere cipher.
76- * @param text text to be encrypted
77- * @param key to be used for encryption
78- * @return new encrypted text
79- */
80- std::string encrypt (const std::string &text, const std::string &key) {
81- std::string encrypted_text = " " // Empty string to store encrypted text
82- // Going through each character of text and key
83- // Note that key is visited in circular way hence j = (j + 1) % |key|
84- for (size_t i = 0 , j = 0 ; i < text.length ();
85- i++, j = (j + 1 ) % key.length ()) {
86- int place_value_text =
87- get_value (text[i]); // Getting value of character in text
88- int place_value_key =
89- get_value (key[j]); // Getting value of character in key
90- place_value_text =
91- (place_value_text + place_value_key) % 26 ; // Applying encryption
92- char encrypted_char = get_char (
93- place_value_text); // Getting new character from encrypted value
94- encrypted_text += encrypted_char; // Appending encrypted character
95- }
96- return encrypted_text; // Returning encrypted text
97- }
98- /* *
99- * Decrypt given text using vigenere cipher.
100- * @param text text to be decrypted
101- * @param key key to be used for decryption
102- * @return new decrypted text
103- */
104- std::string decrypt (const std::string &text, const std::string &key) {
105- // Going through each character of text and key
106- // Note that key is visited in circular way hence j = (j + 1) % |key|
107- std::string decrypted_text = " " // Empty string to store decrypted text
108- for (size_t i = 0 , j = 0 ; i < text.length ();
109- i++, j = (j + 1 ) % key.length ()) {
110- int place_value_text =
111- get_value (text[i]); // Getting value of character in text
112- int place_value_key =
113- get_value (key[j]); // Getting value of character in key
114- place_value_text = (place_value_text - place_value_key + 26 ) %
115- 26 ; // Applying decryption
116- char decrypted_char = get_char (
117- place_value_text); // Getting new character from decrypted value
118- decrypted_text += decrypted_char; // Appending decrypted character
119- }
120- return decrypted_text; // Returning decrypted text
121- }
122- } // namespace vigenere
123- } // namespace ciphers
41+ /* * \namespace vigenere
42+ * \brief Functions for [vigenère cipher](https://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher) algorithm.
43+ */
44+ namespace vigenere {
45+ namespace {
46+ /* *
47+ * This function finds character for given value (i.e.A-Z)
48+ * @param x value for which we want character
49+ * @return corresponding character for perticular value
50+ */
51+ inline char get_char (const int x) {
52+ // By adding 65 we are scaling 0-25 to 65-90.
53+ // Which are in fact ASCII values of A-Z.
54+ return char (x + 65 );
55+ }
56+ /* *
57+ * This function finds value for given character (i.e.0-25)
58+ * @param c character for which we want value
59+ * @return returns corresponding value for perticular character
60+ */
61+ inline int get_value (const char c) {
62+ // A-Z have ASCII values in range 65-90.
63+ // Hence subtracting 65 will scale them to 0-25.
64+ return int (c - 65 );
65+ }
66+ } // Unnamed namespace
67+ /* *
68+ * Encrypt given text using vigenere cipher.
69+ * @param text text to be encrypted
70+ * @param key to be used for encryption
71+ * @return new encrypted text
72+ */
73+ std::string encrypt (const std::string &text, const std::string &key) {
74+ std::string encrypted_text = " " // Empty string to store encrypted text
75+ // Going through each character of text and key
76+ // Note that key is visited in circular way hence j = (j + 1) % |key|
77+ for (size_t i = 0 , j = 0 ; i < text.length (); i++, j = (j + 1 ) % key.length ()) {
78+ int place_value_text = get_value (text[i]); // Getting value of character in text
79+ int place_value_key = get_value (key[j]); // Getting value of character in key
80+ place_value_text = (place_value_text + place_value_key) % 26 ; // Applying encryption
81+ char encrypted_char = get_char (place_value_text); // Getting new character from encrypted value
82+ encrypted_text += encrypted_char; // Appending encrypted character
83+ }
84+ return encrypted_text; // Returning encrypted text
85+ }
86+ /* *
87+ * Decrypt given text using vigenere cipher.
88+ * @param text text to be decrypted
89+ * @param key key to be used for decryption
90+ * @return new decrypted text
91+ */
92+ std::string decrypt (const std::string &text, const std::string &key) {
93+ // Going through each character of text and key
94+ // Note that key is visited in circular way hence j = (j + 1) % |key|
95+ std::string decrypted_text = " " // Empty string to store decrypted text
96+ for (size_t i = 0 , j = 0 ; i < text.length (); i++, j = (j + 1 ) % key.length ()) {
97+ int place_value_text = get_value (text[i]); // Getting value of character in text
98+ int place_value_key = get_value (key[j]); // Getting value of character in key
99+ place_value_text = (place_value_text - place_value_key + 26 ) % 26 ; // Applying decryption
100+ char decrypted_char = get_char (place_value_text); // Getting new character from decrypted value
101+ decrypted_text += decrypted_char; // Appending decrypted character
102+ }
103+ return decrypted_text; // Returning decrypted text
104+ }
105+ } // namespace vigenere
106+ } // namespace ciphers
124107
125108/* *
126109 * Function to test above algorithm
@@ -133,15 +116,15 @@ void test() {
133116 assert (text1 == decrypted1);
134117 std::cout << " Original text : "
135118 std::cout << " , Encrypted text (with key = TESLA) : "
136- std::cout << " , Decrypted text : " << decrypted1 << std::endl;
119+ std::cout << " , Decrypted text : "
137120 // Test 2
138121 std::string text2 = " GOOGLEIT"
139122 std::string encrypted2 = ciphers::vigenere::encrypt (text2, " REALLY"
140123 std::string decrypted2 = ciphers::vigenere::decrypt (encrypted2, " REALLY"
141124 assert (text2 == decrypted2);
142125 std::cout << " Original text : "
143126 std::cout << " , Encrypted text (with key = REALLY) : "
144- std::cout << " , Decrypted text : " << decrypted2 << std::endl;
127+ std::cout << " , Decrypted text : "
145128}
146129
147130/* * Driver Code */
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