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 - SAVE
Explanation 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
Attention reader! Don’t stop learning now. Get hold of all the important Java Foundation and Collections concepts with the Fundamentals of Java and Java Collections Course at a student-friendly price and become industry ready.
