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Keyword Cipher
Keyword cipher is a form of monoalphabetic substitution. A keyword is used as the key, and it determines the letter matchings of the cipher alphabet to the plain alphabet. Repeats of letters in the word are removed, then the cipher alphabet is generated with the keyword matching to A, B, C, etc. until the keyword is used up, whereupon the rest of the ciphertext letters are used in alphabetical order, excluding those already used in the key.
Encryption:
The first line of input contains the keyword which you wish to enter. The second line of input contains the string which you have to encrypt.
Plaintext: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Encrypted: K R Y P T O S A B C D E F G H I J L M N Q U V W X Z
With KRYPTOS as the keyword, all As become Ks, all Bs becoming Rs, and so on. Encrypting the message “knowledge is power” using the keyword “Kryptos”:
Encrypting the message: Knowledge is Power Encoded message: IlmWjbaEb GQ NmWbp
Examples:
Input : Keyword : secret Message : Zombie Here Output : Ciphered String : ZLJEFT DTOT
Take the first example, we used "secret" keyword there. Plain Text : A B C D E F G H I J K L M N O P Q R S T U V W X Y Z When "secret" keyword is used, the new encrypting text becomes : Encrypting : S E C R T A B D F G H I J K L M N O P Q U V W X Y Z This means 'A' means 'S', 'B' means 'E' and 'C' means 'C' and so on. Lets encode the given message "Zombie Here" ZOMBIE HERE becomes ZLJEFT DTOT
Input : Keyword : Star War Message : Attack at dawn Output : Ciphered String : SPPSAG SP RSVJ
Few points to be noted in this method:
- All the messages are encoded in uppercase.
- Whitespace, special characters, and numbers do not take into consideration keywords although you can put them in there.
- While encrypting the message, whitespace, special characters and numbers remain unaffected.
Below is the implementation:
C++
// CPP program for encoding the string// using classical cipher#include<bits/stdc++.h>using namespace std;// Function generates the encoded textstring encoder(string key){ string encoded = ""; // This array represents the // 26 letters of alphabets bool arr[26] = {0}; // This loop inserts the keyword // at the start of the encoded string for (int i=0; i<key.size(); i++) { if(key[i] >= 'A' && key[i] <= 'Z') { // To check whether the character is inserted // earlier in the encoded string or not if (arr[key[i]-65] == 0) { encoded += key[i]; arr[key[i]-65] = 1; } } else if (key[i] >= 'a' && key[i] <= 'z') { if (arr[key[i]-97] == 0) { encoded += key[i] - 32; arr[key[i]-97] = 1; } } } // This loop inserts the remaining // characters in the encoded string. for (int i=0; i<26; i++) { if(arr[i] == 0) { arr[i]=1; encoded += char(i + 65); } } return encoded;}// Function that generates encodes(cipher) the messagestring cipheredIt(string msg, string encoded){ string cipher=""; // This loop ciphered the message. // Spaces, special characters and numbers remain same. for (int i=0; i<msg.size(); i++) { if (msg[i] >='a' && msg[i] <='z') { int pos = msg[i] - 97; cipher += encoded[pos]; } else if (msg[i] >='A' && msg[i] <='Z') { int pos = msg[i] - 65; cipher += encoded[pos]; } else { cipher += msg[i]; } } return cipher;}// Driver codeint main(){ // Hold the Keyword string key; key = "Computer"; cout << "Keyword : " <<key << endl; // Function call to generate encoded text string encoded = encoder(key); // Message that need to encode string message = "GeeksforGeeks"; cout << "Message before Ciphering : " << message << endl; // Function call to print ciphered text cout << "Ciphered Text : " << cipheredIt(message,encoded) << endl; return 0;} |
Java
// Java program for encoding the string// using classical cipherclass GFG{ // Function generates the encoded text static String encoder(char[] key) { String encoded = ""; // This array represents the // 26 letters of alphabets boolean[] arr = new boolean[26]; // This loop inserts the keyword // at the start of the encoded string for (int i = 0; i < key.length; i++) { if (key[i] >= 'A' && key[i] <= 'Z') { // To check whether the character is inserted // earlier in the encoded string or not if (arr[key[i] - 65] == false) { encoded += (char) key[i]; arr[key[i] - 65] = true; } } else if (key[i] >= 'a' && key[i] <= 'z') { if (arr[key[i] - 97] == false) { encoded += (char) (key[i] - 32); arr[key[i] - 97] = true; } } } // This loop inserts the remaining // characters in the encoded string. for (int i = 0; i < 26; i++) { if (arr[i] == false) { arr[i] = true; encoded += (char) (i + 65); } } return encoded; } // Function that generates encodes(cipher) the message static String cipheredIt(String msg, String encoded) { String cipher = ""; // This loop ciphered the message. // Spaces, special characters and numbers remain same. for (int i = 0; i < msg.length(); i++) { if (msg.charAt(i) >= 'a' && msg.charAt(i) <= 'z') { int pos = msg.charAt(i) - 97; cipher += encoded.charAt(pos); } else if (msg.charAt(i) >= 'A' && msg.charAt(i) <= 'Z') { int pos = msg.charAt(i) - 65; cipher += encoded.charAt(pos); } else { cipher += msg.charAt(i); } } return cipher; } // Driver code public static void main(String[] args) { // Hold the Keyword String key; key = "Computer"; System.out.println("Keyword : " + key); // Function call to generate encoded text String encoded = encoder(key.toCharArray()); // Message that need to encode String message = "GeeksforGeeks"; System.out.println("Message before Ciphering : " + message); // Function call to print ciphered text System.out.println("Ciphered Text : " + cipheredIt(message, encoded)); }}// This code is contributed by 29AjayKumar |
C#
// C# program for encoding the string// using classical cipherusing System; class GFG{ // Function generates the encoded text static String encoder(char[] key) { String encoded = ""; // This array represents the // 26 letters of alphabets Boolean[] arr = new Boolean[26]; // This loop inserts the keyword // at the start of the encoded string for (int i = 0; i < key.Length; i++) { if (key[i] >= 'A' && key[i] <= 'Z') { // To check whether the character is inserted // earlier in the encoded string or not if (arr[key[i] - 65] == false) { encoded += (char) key[i]; arr[key[i] - 65] = true; } } else if (key[i] >= 'a' && key[i] <= 'z') { if (arr[key[i] - 97] == false) { encoded += (char) (key[i] - 32); arr[key[i] - 97] = true; } } } // This loop inserts the remaining // characters in the encoded string. for (int i = 0; i < 26; i++) { if (arr[i] == false) { arr[i] = true; encoded += (char) (i + 65); } } return encoded; } // Function that generates encodes(cipher) the message static String cipheredIt(String msg, String encoded) { String cipher = ""; // This loop ciphered the message. // Spaces, special characters and numbers remain same. for (int i = 0; i < msg.Length; i++) { if (msg[i] >= 'a' && msg[i] <= 'z') { int pos = msg[i] - 97; cipher += encoded[pos]; } else if (msg[i] >= 'A' && msg[i] <= 'Z') { int pos = msg[i] - 65; cipher += encoded[pos]; } else { cipher += msg[i]; } } return cipher; } // Driver code public static void Main(String[] args) { // Hold the Keyword String key; key = "Computer"; Console.WriteLine("Keyword : " + key); // Function call to generate encoded text String encoded = encoder(key.ToCharArray()); // Message that need to encode String message = "GeeksforGeeks"; Console.WriteLine("Message before Ciphering : " + message); // Function call to print ciphered text Console.WriteLine("Ciphered Text : " + cipheredIt(message, encoded)); }}/* This code contributed by PrinciRaj1992 */ |
Javascript
<script>// JavaScript program for encoding the string// using classical cipher// Function generates the encoded textfunction encoder(key){ let encoded = ""; // This array represents the // 26 letters of alphabets let arr = new Array(26); for(let i=0;i<26;i++) { arr[i]=false; } // This loop inserts the keyword // at the start of the encoded string for (let i = 0; i < key.length; i++) { if (key[i].charCodeAt(0) >= 'A'.charCodeAt(0) && key[i].charCodeAt(0) <= 'Z'.charCodeAt(0)) { // To check whether the character is inserted // earlier in the encoded string or not if (arr[key[i].charCodeAt(0) - 65] == false) { encoded += ( key[i]); arr[key[i].charCodeAt(0) - 65] = true; } } else if (key[i].charCodeAt(0) >= 'a'.charCodeAt(0) && key[i].charCodeAt(0) <= 'z'.charCodeAt(0)) { if (arr[key[i].charCodeAt(0) - 97] == false) { encoded += String.fromCharCode(key[i].charCodeAt(0) - 32); arr[key[i].charCodeAt(0) - 97] = true; } } } // This loop inserts the remaining // characters in the encoded string. for (let i = 0; i < 26; i++) { if (arr[i] == false) { arr[i] = true; encoded += String.fromCharCode(i + 65); } } return encoded;}// Function that generates encodes(cipher) the messagefunction cipheredIt(msg,encoded){ let cipher = ""; // This loop ciphered the message. // Spaces, special characters and numbers remain same. for (let i = 0; i < msg.length; i++) { if (msg[i] >= 'a' && msg[i] <= 'z') { let pos = msg[i].charCodeAt(0) - 97; cipher += encoded[pos]; } else if (msg[i] >= 'A' && msg[i] <= 'Z') { let pos = msg[i].charCodeAt(0) - 65; cipher += encoded[pos]; } else { cipher += msg[i]; } } return cipher;}// Driver code// Hold the Keywordlet key;key = "Computer";document.write("Keyword : " + key+"<br>");// Function call to generate encoded textlet encoded = encoder(key.split(""));// Message that need to encodelet message = "GeeksforGeeks";document.write("Message before Ciphering : " + message+"<br>");// Function call to print ciphered textdocument.write("Ciphered Text : " + cipheredIt(message, encoded));// This code is contributed by rag2127</script> |
Python3
# Python program for encoding the string# using classical cipherimport string# stores all upper case alphabetsall_alphabets = list(string.ascii_uppercase)keyword = "Star War"keyword1 = keyword.upper()message = "Attack at dawn"# converts message to listmsg = []for i in message: msg.append(i.upper())# removes default elementsdef duplicates(list): key = [] for i in list: if i not in key: key.append(i) return keykeyword1 = duplicates(keyword1)# Stores the encryption listencrypting = duplicates(keyword1+all_alphabets)# removes spaces from the encryption listfor i in encrypting: if(i == ' '): encrypting.remove(' ')ciphertext = ""# maps each element of the message to the encryption list and stores it in ciphertextfor i in range(len(msg)): if(msg[i] != ' '): ciphertext = ciphertext+encrypting[all_alphabets.index(msg[i])] else: ciphertext = ciphertext+' 'print("Keyword : ", keyword)print("Message before Ciphering : ", message)print("Ciphered Text : ", ciphertext)# This code is contributed by Pranay Arora |
Output
Keyword : Computer Message before Ciphering : GeeksforGeeks Ciphered Text : EUUDNTILEUUDN
Decryption:
To decode the message you check the position of the given message in encrypting text with the plain text.
Plaintext: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Encrypted: K R Y P T O S A B C D E F G H I J L M N Q U V W X Z
Message: PTYBIATLEP Deciphered Text: DECIPHERED
Now, how do we generate the deciphered string? We search for ‘P’ in Encrypted Text and compare its position with plain text letter and generate that letter. So ‘P’ becomes ‘D’, ‘T’ becomes ‘E’, ‘Y’ becomes ‘C’, and so on.
Examples:
Input : Keyword : secret Message : zljeft dtOT Output : Deciphered String : ZOMBIE HERE Input : Keyword : joker0O7hack123 Message : QjTijl Output : Deciphered String : BATMAN
Below is the implementation:
Example 1
CPP
// CPP program for decoding the string// which generate using classical cipher#include <bits/stdc++.h>using namespace std;// Original Set of lettersstring plaintext = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";// Function generates the encoded textstring encoder(string key){ string encoded = ""; bool arr[26] = { 0 }; // This loop inserts the keyword // at the start of the encoded string for (int i = 0; i < key.size(); i++) { if (key[i] >= 'A' && key[i] <= 'Z') { // To check whether the character is inserted // earlier in the encoded string or not if (arr[key[i] - 65] == 0) { encoded += key[i]; arr[key[i] - 65] = 1; } } else if (key[i] >= 'a' && key[i] <= 'z') { if (arr[key[i] - 97] == 0) { encoded += key[i] - 32; arr[key[i] - 97] = 1; } } } // This loop inserts the remaining // characters in the encoded string. for (int i = 0; i < 26; i++) { if (arr[i] == 0) { arr[i] = 1; encoded += char(i + 65); } } return encoded;}// This function will decode the messagestring decipheredIt(string msg, string encoded){ // Hold the position of every character (A-Z) // from encoded string map<char, int> enc; for (int i = 0; i < encoded.size(); i++) { enc[encoded[i]] = i; } string decipher = ""; // This loop deciphered the message. // Spaces, special characters and numbers remain same. for (int i = 0; i < msg.size(); i++) { if (msg[i] >= 'a' && msg[i] <= 'z') { int pos = enc[msg[i] - 32]; decipher += plaintext[pos]; } else if (msg[i] >= 'A' && msg[i] <= 'Z') { int pos = enc[msg[i]]; decipher += plaintext[pos]; } else { decipher += msg[i]; } } return decipher;}// Driver codeint main(){ // Hold the Keyword string key; key = "Computer"; cout << "Keyword : " << key << endl; // Function call to generate encoded text string encoded = encoder(key); // Message that need to decode string message = "EUUDN TIL EUUDN"; cout << "Message before Deciphering : " << message << endl; // Function call to print deciphered text cout << "Ciphered Text : " << decipheredIt(message, encoded) << endl; return 0;} |
Java
// Java program for decoding the string// using classical cipher import java.util.HashMap;import java.util.Map;class GFG{ // Function generates the encoded text public static String encoder(char[] key) { String encoded = ""; // This array represents the // 26 letters of alphabets boolean[] arr = new boolean[26]; // This loop inserts the keyword // at the start of the encoded string for (int i = 0; i < key.length; i++) { if (key[i] >= 'A' && key[i] <= 'Z') { // To check whether the character is inserted // earlier in the encoded string or not if (arr[key[i] - 65] == false) { encoded += (char) key[i]; arr[key[i] - 65] = true; } } else if (key[i] >= 'a' && key[i] <= 'z') { if (arr[key[i] - 97] == false) { encoded += (char) (key[i] - 32); arr[key[i] - 97] = true; } } } // This loop inserts the remaining // characters in the encoded string. for (int i = 0; i < 26; i++) { if (arr[i] == false) { arr[i] = true; encoded += (char) (i + 65); } } return encoded; } // This function will decode the message public static String decipheredIt(String msg, String input) { // Original Set of letters String plaintext = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; String decipher = ""; // Hold the position of every character (A-Z) from encoded string Map<Character, Integer> enc = new HashMap<>(); for (int i = 0; i < input.length(); i++) { enc.put(input.charAt(i), i); } // This loop deciphered the message. // Spaces, special characters and numbers remain same. for (int i = 0; i < msg.length(); i++) { if (msg.charAt(i) >= 'a' && msg.charAt(i) <= 'z') { int pos = enc.get((char)(msg.charAt(i)-32)); decipher += plaintext.charAt(pos); } else if (msg.charAt(i) >= 'A' && msg.charAt(i) <= 'Z') { int pos = enc.get(msg.charAt(i)); decipher += plaintext.charAt(pos); } else { decipher += msg.charAt(i); } } return decipher; } // Driver code public static void main(String[] args) { // Hold the Keyword String key; key = "Computer"; System.out.println("Keyword : " + key); // Function call to generate encoded text String decoded = encoder(key.toCharArray()); // Message that need to encode String message = "EUUDN TIL EUUDN"; System.out.println("Message before Deciphering : " + message); // Function call to print ciphered text System.out.println("Ciphered Text : " + decipheredIt(message, decoded)); }}// This code is contributed by javierdsv |
Output
Keyword : Computer Message before Deciphering : EUUDN TIL EUUDN Ciphered Text : GEEKS FOR GEEKS
Example 2
Python
# Python Program for Decoding the String# using Classical Cipherimport string# stores all upper case alphabetsall_alphabets = list(string.ascii_uppercase)keyword = "Star War"keyword1 = keyword.upper()ciphertext = "SPPSAG SP RSVJ"# converts message to listct = []for i in ciphertext: ct.append(i.upper())# removes default elementsdef duplicates(list): key = [] for i in list: if i not in key: key.append(i) return keykeyword1 = duplicates(keyword1)# Stores the encryption listencrypting = duplicates(keyword1+all_alphabets)# removes spaces from the encryption listfor i in encrypting: if(i == ' '): encrypting.remove(' ')# maps each element of the message to the encryption list and stores it in ciphertextmessage = ""for i in range(len(ct)): if(ct[i] != ' '): message = message+all_alphabets[encrypting.index(ct[i])] else: message = message+' 'print("Keyword : ", keyword)print("Ciphered Text : ", ciphertext)print("Message before Ciphering : ", message) |
Output
('Keyword : ', 'Star War')
('Ciphered Text : ', 'SPPSAG SP RSVJ')
('Message before Ciphering : ', 'ATTACK AT DAWN')Note: One can improve this Classical Cipher: Keyword also. Here we are only taking A-Z in plain text. You can take uppercase, lowercase, and numbers also into consideration.
Ways to attack a keyword cipher:
The best ways to attack a keyword cipher without knowing the keyword are through the known-plaintext attack, frequency analysis, and discovery of the keyword (often a cryptanalyst will combine all three techniques). Keyword discovery allows immediate decryption since the table can be made immediately.
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