# Alternated Caesar Cipher

I've recently picked up PHP, for the first assignment in my IT-security class I decided to code it in PHP. The algorithm is an alternation of the Caesar cipher, instead of using a fixed number to push the letters a keyword is applied to rearrange a couple of letters and then move the rest of the letters accordingly.

I am pretty sure there can be improvements in string usage and probably also in the algorithm? Any ideas and notes on programming style and such are very welcome.

or:

<?php
class encrypt
{
private $key; private$uword;
private $eword; private$letters;

/**
* Constructor.
*
* Creates the $letters array. */ function __construct() { for($i=0;$i<26;$i++)
{
$this->letters[$i][0] = chr(65+$i);$this->letters[$i][1] = 0; } for($i=26;$i<52;$i++)
{
$this->letters[$i][0] = chr(97+$i-26);$this->letters[$i][1] = 0; } for($i=52;$i<62;$i++)
{
$this->letters[$i][0] = $i-52;$this->letters[$i][1] = 0; }$this->letters[62][0] = ' ';
$this->letters[62][1] = 0; } /** * Encrypts the key using an alternation of the caesar cipher. * The key is used to set a different alternation for the letters, instead * of having it moved by a constant number. * * @throws Exception - if there is no key * @return string - returns the encrypted alphabet as array */ private function _encrypt() { if(empty($this->key))
{
throw new Exception("Empty key: cannot create encryption without a key.");
}

$key =$this->key;
$letters =$this->letters;

$encryption = array_fill(0, 63, '');$pos = 0;

//add key to encoding. each letter only once, though
for($i=0;$i<strlen($key);$i++)
{
$c = substr($key, $i, 1);$do = true;

//only add letter if it hasn't been used yet
for($j=0;$j<count($encryption);$j++)
{
if(!strcmp($encryption[$j], $c))$do=false;
}

if($do)$encryption[$pos] =$c;

//find letters that have already been used
for($j=0;$j<63;$j++) { if(!strcmp($letters[$j][0],$encryption[$pos])) {$letters[$j][1] = 1; } } if($do) $pos++; } //add all the unused letters to the encoding array$k=63;
for($i=$pos;$i<63;$i++)
{
$continue=true; for($j=63-$k;$j<63 && $continue;$j++)
{
if($letters[$j][1]==0)
{
$encryption[$i] = $letters[$j][0];
$letters[$j][1] = 1;
$continue = false; --$k;
}
}
}

//reset letter's usage
for($i=0;$i<63;$i++) {$this->letters[$i][1] = 0; } return$encryption;
}

/**
* Encrypts the given word.
*
* @throws Exception - if there is no unencrypted word
* @return string - Encrypted word
*/
public function encrypt()
{
if(empty($this->uword)) { throw new Exception("Empty word: cannot encrypt a non-existend word."); }$encryption = $this->_encrypt();$uword = $this->uword;$eword = '';
$letters =$this->letters;

for($i=0;$i<strlen($uword);$i++)
{
$c = substr($uword, $i, 1); for($j=0;$j<63;$j++)
{
if(!strcmp($letters[$j][0], $c)) {$eword .= $encryption[$j];
}
}
}
$this->eword =$eword;
return $eword; } /** * Decrypts the given encryption. * * @throws Exception - if there is no encrypted word * @return string - Encrypted word */ public function decrypt() { if(empty($this->eword))
{
throw new Exception("Empty encryption: cannot decrypt a non-existend word.");
}

$encryption =$this->_encrypt();
$eword =$this->eword;
$uword = '';$letters = $this->letters; for($i=0;$i<strlen($eword);$i++) {$c = substr($eword,$i, 1);

for($j=0;$j<63;$j++) { if(!strcmp($encryption[$j],$c))
{
$uword .=$letters[$j][0]; } } }$this->uword = $uword; return$uword;
}

/**
*
* @param unknown_type $key - keyword for encryption */ public function setKey($key)
{
$this->key =$key;
}

/**
*
* @param unknown_type $uword - unencrypted word */ public function setUword($uword)
{
$this->uword =$uword;
}

/**
*
* @param unknown_type $eword - encrypted word */ public function setEword($eword)
{
$this->eword =$eword;
}

/**
*
* @return - $key */ public function getKey() { return$this->key;
}

/**
*
* @return - $uword */ public function getUword() { return$this->uword;
}
/**
*
* @return - $eword */ public function getEword() { return$this->eword;
}
}
?>
• Welcome to CodeReview.SE. Please have a look at the codereview.stackexchange.com/faq . Among other things, please make sure you include your code in the question. Enjoy! – SylvainD Mar 30 '13 at 10:10

Give the class a better name... a noun makes more sense than a verb.

Consider simply removing the $uword and$eword properties and applicable setter methods. Instead, your encrypt method signature could be:

/**
* @param string $uword word to encrypt * @return string encrypted word */ public function encrypt($uword)
...

Do the same with decrypt:

/**
* @param string $eword word to decrypt * @return string decrypted word */ public function decrypt($eword)
...

Put a $key argument in the constructor: public function __construct($key)
{
$this->key =$key;
...

With the $key invariant satisfied, no need to throw an exception if not set. Remove the setKey/getKey methods (unless you really need them). Cleaner calling code example:$cipher = new CeaserCipher('my key, get this from where ever');
$encryptedValue =$cipher->encrypt('foo');

$decryptedValue =$cipher->decrypt(\$encryptedValue);
• thanks for your input, I will consider all of this in future projects. Funnily enough, when I eventually implemented it into Qt C++ using QByteArrays and its methods the code shrunk from this massive size to just a couple of lines. – LML May 16 '13 at 20:01