CypherText.java

/*
 * $Id: CypherText.java,v 1.4 2006/04/09 12:13:13 laddi Exp $
 *
 * Copyright (C) 2001 Idega hf. All Rights Reserved.
 *
 * This software is the proprietary information of Idega hf.
 * Use is subject to license terms.
 *
 */
package com.idega.util;

/**
 *
 * @author <a href="mailto:palli@idega.is">Pall Helgason</a>
 * @version 1.0
 */
public class CypherText {
  private final String alphabet_ = "nk2cmqYgidw9spTuyDXFZt4HA8Ma3xEr75QClBV0IUPo6LezWNbOv1SjRfJGKh";
  private String cypherKey_ = null;

  public CypherText() {
  }

  /**
   *
   */
  public String doCyper(String text, String cypherKey) throws NullPointerException {
    setKey(cypherKey);

    return(cypher(text));
  }

  /**
   *
   */
  public String doDeCypher(String text, String cypherKey) throws NullPointerException {
    setKey(cypherKey);

    return(deCypher(text));
  }

  /**
   * Returns the current cypher key for this object. If the cypher key is null
   * a new cypher key is created and returned.
   *
   * @param
   *
   * @return
   */
  public String getKey(int length) {
    if (this.cypherKey_ == null) {
			createKey(length);
		}

    if (this.cypherKey_.length() != length) {
			createKey(length);
		}

    return(this.cypherKey_);
  }

  /**
   *
   */
  public void setKey(String key) throws NullPointerException {
    if (key == null) {
			throw(new NullPointerException("Cypher key is null"));
		}

    this.cypherKey_ = key;
  }

  /*
   *
   */
  private void createKey(int length) {
    StringBuffer key = new StringBuffer();
    for (int i = 0; i < length; i++) {
      char rnd = (char)(Math.random() * this.alphabet_.length());
      key.append(this.alphabet_.charAt(rnd));
    }

    this.cypherKey_ = key.toString();
  }

  /*
   *
   */
  private String cypher(String text) throws NullPointerException, IllegalArgumentException {
    if (text == null) {
			throw(new NullPointerException("No text to cypher"));
		}

    boolean isAlphabet = checkAlphabet(text);
    if (!isAlphabet) {
			throw(new IllegalArgumentException("Text contains characters which are not cypherable. Please use only [a..z][A..Z][0..9]"));
		}

    StringBuffer cyphered = new StringBuffer();

    while (this.cypherKey_.length() < text.length()) {
			this.cypherKey_ = this.cypherKey_.concat(this.cypherKey_);
		}

    for (int i = 0; i < text.length(); i++) {
      int a = getIntValue(text.charAt(i));
      int b = getIntValue(this.cypherKey_.charAt(i));
      int c = (a + b) % this.alphabet_.length();

      cyphered.append(this.alphabet_.charAt(c));
    }

    String reversed = cyphered.toString();
    reversed = reverse(reversed);

    return(reversed);
  }

  /*
   *
   */
  public String reverse(String text) {
    String ret = new String();
    for (int i = text.length() - 1; i >= 0; i--) {
			ret = ret.concat(String.valueOf(text.charAt(i)));
		}

    return(ret);
  }

  /*
   *
   */
  private boolean checkAlphabet(String text) {
    for (int i = 0; i < this.alphabet_.length(); i++) {
			text = text.replace(this.alphabet_.charAt(i),' ');
		}

    text = text.trim();
    if ((text == null) || (text.equalsIgnoreCase(""))) {
			return(true);
		}
		else {
			return(false);
		}
  }

  /*
   *
   */
  private String deCypher(String cypherText) throws NullPointerException {
    if (cypherText == null) {
			throw(new NullPointerException("No text to decypher"));
		}

    StringBuffer decyphered = new StringBuffer();
    cypherText = reverse(cypherText);

    while (this.cypherKey_.length() < cypherText.length()) {
			this.cypherKey_ = this.cypherKey_.concat(this.cypherKey_);
		}

    for (int i = 0; i < cypherText.length(); i++) {
      int a = getIntValue(cypherText.charAt(i));
      int b = getIntValue(this.cypherKey_.charAt(i));
      int c = (a - b) % this.alphabet_.length();

      while (c < 0) {
        c += this.alphabet_.length();
      }

      decyphered.append(this.alphabet_.charAt(c));
    }

    return(decyphered.toString());
  }

  /*
   *
   */
  private int getIntValue(char a) {
    int i = this.alphabet_.indexOf(a);

    return(i);
  }
}