Vigenere Cipher

1. 2. package com.sanfoundry.setandstring; 3. 4. public class VigenereCipher 5. { 6. public static String encrypt(String text, final String key) 7. { 8. String res = ""; 9. text = text.toUpperCase(); 10. for (int i = 0, j = 0; i < text.length(); i++) 11. { 12. char c = text.charAt(i); 13. if (c < 'A' || c > 'Z') 14. continue; 15. res += (char) ((c + key.charAt(j) - 2 * 'A') % 26 + 'A'); 16. j = ++j % key.length(); 17. } 18. return res; 19. } 20. 21. public static String decrypt(String text, final String key) 22. { 23. String res = ""; 24. text = text.toUpperCase(); 25. for (int i = 0, j = 0; i < text.length(); i++) 26. { 27. char c = text.charAt(i); 28. if (c < 'A' || c > 'Z') 29. continue; 30. res += (char) ((c - key.charAt(j) + 26) % 26 + 'A'); 31. j = ++j % key.length(); 32. } 33. return res; 34. } 35. 36. public static void main(String[] args) 37. { 38. String key = "VIGENERECIPHER"; 39. String message = "Beware the Jabberwock, my son! The jaws that bite, the claws that catch!"; 40. String encryptedMsg = encrypt(message, key); 41. System.out.println("String: " + message); 42. System.out.println("Encrypted message: " + encryptedMsg); 43. System.out.println("Decrypted message: " + decrypt(encryptedMsg, key)); 44. } 45. }

Output: $ javac VigenereCipher.java $ java VigenereCipher String: Beware the Jabberwock, my son! The jaws that bite, the claws that catch! Encrypted message: WMCEEIKLGRPIFVMEUGXQPWQVIOIAVEYXUEKFKBTALVXTGAFXYEVKPAGY Decrypted message: BEWARETHEJABBERWOCKMYSONTHEJAWSTHATBITETHECLAWSTHATCATCH