One Time Pad algorithm is also known as Vernam Cipher. It is a method of encrypting alphabetic plain text. It is one of the Transposition techniques which converts plain text into ciphertext. In this mechanism, we assign a number to each character of the Plain-Text.
Assignment is as follows: A B C D E F G H I J 0 1 2 3 4 5 6 7 8 9 K L M N O P Q R S T 10 11 12 13 14 15 16 17 18 19 U V W X Y Z 20 21 22 23 24 25
The relation between the key and plain text: In this algorithm, the length of the key should be equal to that of plain text.
Examples:
Input: plain text - HELLO
Key - MONEY
Output: Cipher - TSYPM
Message - HELLO
Input: plain text - SAVE
Key - LIFE
Output: Cipher - DIAI
Message - SAVEExplanation of the above:
Part 1 (plain text to cipher text)
Plain text — H E L L O → 7 4 11 11 14
Key — M O N E Y → 12 14 13 4 24
Plain text + key → 19 18 24 15 38
→ 19 18 24 15 12 (=38 – 26)
Cipher Text → T S Y P M
Part 2 (cipher text to Message)
Cipher Text — T S Y P M → 19 18 24 15 12
Key — M O N E Y→ 12 14 13 4 24
Cipher text – key → 7 4 11 11 -12
→ 7 4 11 11 14
Message → H E L L O
Java
// Java program which implements// one time pad algorithm import java.io.*;public class GFG { // function which returns encryptedText public static String stringEncryption(String text, String key) { // initializing cipherText String cipherText = ""; // initialize cipher array of key length // which stores the sum of corresponding no.'s // of plainText and key. int cipher[] = new int[key.length()]; for (int i = 0; i < key.length(); i++) { cipher[i] = text.charAt(i) - 'A' + key.charAt(i) - 'A'; } // if the sum is greater than 25 // subtract 26 from it and store that resulting // value for (int i = 0; i < key.length(); i++) { if (cipher[i] > 25) { cipher[i] = cipher[i] - 26; } } // convert the no.'s into integers // convert these integers to corresponding // characters and add them up to cipherText for (int i = 0; i < key.length(); i++) { int x = cipher[i] + 'A'; cipherText += (char)x; } // returning the cipherText return cipherText; } // function which returns plainText public static String stringDecryption(String s,String key) { // initializing plainText String plainText = ""; // initializing integer array of key length // which stores difference of corresponding no.'s of // each character of cipherText and key int plain[] = new int[key.length()]; // running for loop for each character // subtracting and storing in the array for (int i = 0; i < key.length(); i++) { plain[i]= s.charAt(i) - 'A' - (key.charAt(i) - 'A'); } // if the difference is less than 0 // add 26 and store it in the array. for (int i = 0; i < key.length(); i++) { if (plain[i] < 0) { plain[i] = plain[i] + 26; } } // convert int to corresponding char // add them up to plainText for (int i = 0; i < key.length(); i++) { int x = plain[i] + 'A'; plainText += (char)x; } // returning plainText return plainText; } // main function public static void main(String[] args) { // declaration of plain text String plainText = "Hello"; // declaration of key String key = "MONEY"; // converting plain text to toUpperCase // function call to stringEncryption // with plainText and key as parameters String encryptedText = stringEncryption(plainText.toUpperCase(), key.toUpperCase()); // printing cipher Text System.out.println("Cipher Text - "+ encryptedText); // function call to stringDecryption // with encryptedText and key as parameters System.out.println("Message - " + stringDecryption(encryptedText, key.toUpperCase())); }} |
Cipher Text - TSYPM Message - HELLO
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