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Added AffineCipher algorithm to Ciphers #2668

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Merged
siriak merged 3 commits into from
Oct 18, 2021
Merged

Added AffineCipher algorithm to Ciphers #2668

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vatsal-dp Oct 18, 2021
00df978
Update AffineCipher.java
vatsal-dp Oct 18, 2021
421439b
Merge branch 'master' into master
siriak Oct 18, 2021
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98 changes: 98 additions & 0 deletions Ciphers/AffineCipher.java
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Original file line number Diff line number Diff line change
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//The ‘key’ for the Affine cipher consists of 2 numbers, we’ll call them a and b.
// The following discussion assumes the use of a 26 character alphabet (m = 26).
// a should be chosen to be relatively prime to m (i.e. a should have no factors in common with m).

package Ciphers;

import java.util.Scanner;

class AffineCipher
{
static Scanner in = new Scanner(System.in);

static String encryptMessage(char[] msg)
{
System.out.println("Enter key value a for encryption : ");
int a = in.nextInt();

System.out.println("Enter key value b for encryption : ");
int b = in.nextInt();

/// Initially empty cipher String
String cipher = "";
for (int i = 0; i < msg.length; i++)
{
// Avoid space to be encrypted
/* applying encryption formula ( a x + b ) mod m
{here x is msg[i] and m is 26} and added 'A' to
bring it in range of ascii alphabet[ 65-90 | A-Z ] */
if (msg[i] != ' ')
{
cipher = cipher
+ (char) ((((a * (msg[i] - 'A')) + b) % 26) + 'A');
} else // append space character
{
cipher += msg[i];
}
}
return cipher;
}

static String decryptCipher(String cipher)
{
System.out.println("Enter key value a for decryption : ");
int a = in.nextInt();

System.out.println("Enter key value b for decryption : ");
int b = in.nextInt();

String msg = "";
int a_inv = 0;
int flag = 0;

//Find a^-1 (the multiplicative inverse of a
//in the group of integers modulo m.)
for (int i = 0; i < 26; i++)
{
flag = (a * i) % 26;

// Check if (a*i)%26 == 1,
// if so, then i will be the multiplicative inverse of a
if (flag == 1)
{
a_inv = i;
}
}
for (int i = 0; i < cipher.length(); i++)
{
/*Applying decryption formula a^-1 ( x - b ) mod m
{here x is cipher[i] and m is 26} and added 'A'
to bring it in range of ASCII alphabet[ 65-90 | A-Z ] */
if (cipher.charAt(i) != ' ')
{
msg = msg + (char) (((a_inv *
((cipher.charAt(i) + 'A' - b)) % 26)) + 'A');
}
else // append space character
{
msg += cipher.charAt(i);
}
}

return msg;
}

// Main method
public static void main(String[] args)
{
String msg = "AFFINE CIPHER";

// Encrypting message
String cipherText = encryptMessage(msg.toCharArray());
System.out.println("Encrypted Message is : " + cipherText);

// Decrypting message
System.out.println("Decrypted Message is: " + decryptCipher(cipherText));

}
}