SubstitutionScheme.java

package DiffieHellman;

public class SubstitutionScheme 
{
  private static final int SMALLEST_CHAR_DECIMAL_VALUE = 32;
  
  /**
   *Key required to encrypt and decrypt the message.
   */
  private final String Key;
  
  public SubstitutionScheme(String Key) 
  {
    this.Key = Key;
  }
  
  /**
    *Encrypts the plaintext by substitution. 
    */

  public String encrypt(String plaintext) 
  {
    String cipher = "";
    for (char c : plaintext.toCharArray()) 
    {
      cipher += Key.charAt((int) c - SMALLEST_CHAR_DECIMAL_VALUE);
    }
    
    return cipher;
  }
  
  /**
    *Decrypts the ciphertext by reversing the process of the encryption.
    */
  public String decrypt(String ciphertext) 
  {
    String text = "";
    for (char c : ciphertext.toCharArray()) 
    {
      text += (char) (Key.indexOf((int) c) + SMALLEST_CHAR_DECIMAL_VALUE);
    }
    
    return text;
  }
}