两组简单的PHP解密解密代码
http://www.phper.org.cn/?post=133
加密算法如下：

function encrypt($data, $key)
{
	$key	=	md5($key);
    $x		=	0;
    $len	=	strlen($data);
    $l		=	strlen($key);
    for ($i = 0; $i < $len; $i++)
    {
        if ($x == $l) 
        {
        	$x = 0;
        }
        $char .= $key{$x};
        $x++;
    }
    for ($i = 0; $i < $len; $i++)
    {
        $str .= chr(ord($data{$i}) + (ord($char{$i})) % 256);
    }
    return base64_encode($str);
}

解密算法如下：

function decrypt($data, $key)
{
	$key = md5($key);
    $x = 0;
    $data = base64_decode($data);
    $len = strlen($data);
    $l = strlen($key);
    for ($i = 0; $i < $len; $i++)
    {
        if ($x == $l) 
        {
        	$x = 0;
        }
        $char .= substr($key, $x, 1);
        $x++;
    }
    for ($i = 0; $i < $len; $i++)
    {
        if (ord(substr($data, $i, 1)) < ord(substr($char, $i, 1)))
        {
            $str .= chr((ord(substr($data, $i, 1)) + 256) - ord(substr($char, $i, 1)));
        }
        else
        {
            $str .= chr(ord(substr($data, $i, 1)) - ord(substr($char, $i, 1)));
        }
    }
    return $str;
}

使用:

$data = 'PHP加密解密算法';		// 被加密信息
$key = '123';					// 密钥
$encrypt = encrypt($data, $key);
$decrypt = decrypt($encrypt, $key);
echo $encrypt, "\n", $decrypt;

http://www.thinkphp.cn/code/282.html

/**
 * 通用加密
 * @param String $string 需要加密的字串
 * @param String $skey 加密EKY
 * @author Anyon Zou <zoujingli@echounion.com>
 * @date 2013-08-13 19:30
 * @return String
 */
 function enCode($string = '', $skey = 'echounion') {
    $skey = array_reverse(str_split($skey));
    $strArr = str_split(base64_encode($string));
    $strCount = count($strArr);
    foreach ($skey as $key => $value) {
        $key < $strCount && $strArr[$key].=$value;
    }
    return str_replace('=', 'O0O0O', join('', $strArr));
 }
 /**
 * 通用解密
 * @param String $string 需要解密的字串
 * @param String $skey 解密KEY
 * @return String
 * @author Anyon Zou <zoujingli@echounion.com>
 * @date 2013-08-13 19:30
 */
 function deCode($string = '', $skey = 'echounion') {
    $skey = array_reverse(str_split($skey));
    $strArr = str_split(str_replace('O0O0O', '=', $string), 2);
    $strCount = count($strArr);
    foreach ($skey as $key => $value) {
        $key < $strCount && $strArr[$key] = rtrim($strArr[$key], $value);
    }
    return base64_decode(join('', $strArr));
 }