84 lines
2.3 KiB
Java
84 lines
2.3 KiB
Java
package Ciphers;
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class affineCipher
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{
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// Key values of a and b
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static int a = 17;
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static int b = 20;
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static String encryptMessage(char[] msg)
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{
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/// Cipher Text initially empty
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String cipher = "";
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for (int i = 0; i < msg.length; i++)
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{
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// Avoid space to be encrypted
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/* applying encryption formula ( a x + b ) mod m
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{here x is msg[i] and m is 26} and added 'A' to
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bring it in range of ascii alphabet[ 65-90 | A-Z ] */
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if (msg[i] != ' ')
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{
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cipher = cipher
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+ (char) ((((a * (msg[i] - 'A')) + b) % 26) + 'A');
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} else // else simply append space character
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{
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cipher += msg[i];
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}
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}
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return cipher;
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}
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static String decryptCipher(String cipher)
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{
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String msg = "";
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int a_inv = 0;
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int flag = 0;
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//Find a^-1 (the multiplicative inverse of a
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//in the group of integers modulo m.)
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for (int i = 0; i < 26; i++)
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{
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flag = (a * i) % 26;
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// Check if (a*i)%26 == 1,
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// then i will be the multiplicative inverse of a
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if (flag == 1)
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{
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a_inv = i;
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}
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}
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for (int i = 0; i < cipher.length(); i++)
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{
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/*Applying decryption formula a^-1 ( x - b ) mod m
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{here x is cipher[i] and m is 26} and added 'A'
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to bring it in range of ASCII alphabet[ 65-90 | A-Z ] */
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if (cipher.charAt(i) != ' ')
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{
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msg = msg + (char) (((a_inv *
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((cipher.charAt(i) + 'A' - b)) % 26)) + 'A');
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}
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else //else simply append space character
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{
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msg += cipher.charAt(i);
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}
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}
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return msg;
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}
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// Driver code
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public static void main(String[] args)
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{
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String msg = "AFFINE CIPHER";
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// Calling encryption function
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String cipherText = encryptMessage(msg.toCharArray());
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System.out.println("Encrypted Message is : " + cipherText);
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// Calling Decryption function
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System.out.println("Decrypted Message is: " + decryptCipher(cipherText));
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}
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}
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