PHP加密解密数字，适用于URL加密。

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<?php
/**
 * 加密解密类
 * 该算法仅支持加密数字。比较适用于数据库中id字段的加密解密，以及根据数字显示url的加密。
 * @author 深秋的竹子
 * @email  81254648@qq.com
 * @version alpha
 * @加密原则 标记长度 + 补位 + 数字替换
 * @加密步骤：
 * 将a-z,A-Z,0-9 62个字符打乱，取前M(数字最大的位数)位作为 标记长度字符串，取第M+1 到第M+10位为数字替换字符串，剩余的为补位字符串
 * 1.计算数字长度n,取乱码的第n位作为标记长度。
 * 2.计算补位的长度，加密串的长度N -1 - n 为补位的长度。根据指定的算法得到补位字符串。
 * 3.根据数字替换字符串替换数字，得到数字加密字符串。
 * 标记长度字符 + 补位字符串 + 数字加密字符串 = 加密串
 * Usage:
 *      $obj = new XDeode(9);
 *      $e_txt = $obj->encode(123);
 *      echo $e_txt.'<br/>';
 *      echo $key->decode($e_txt);
 */

class XDeode{
	private $strbase = "Flpvf70CsakVjqgeWUPXQxSyJizmNH6B1u3b8cAEKwTd54nRtZOMDhoG2YLrI";
	private $key,$length,$codelen,$codenums,$codeext;
	function __construct($length = 9,$key = 2543.5415412812){
		$this->key = $key;
		$this->length = $length;
		$this->codelen = substr($this->strbase,0,$this->length);
		$this->codenums = substr($this->strbase,$this->length,10);
		$this->codeext = substr($this->strbase,$this->length + 10);
	}

	function encode($nums){
		$rtn = "";
		$numslen = strlen($nums);
		//密文第一位标记数字的长度
		$begin = substr($this->codelen,$numslen - 1,1);

		//密文的扩展位
		$extlen = $this->length - $numslen - 1;
		$temp = str_replace('.', '', $nums / $this->key);
		$temp = substr($temp,-$extlen);

		$arrextTemp = str_split($this->codeext);
		$arrext = str_split($temp);
		foreach ($arrext as $v) {
			$rtn .= $arrextTemp[$v];
		}

		$arrnumsTemp = str_split($this->codenums);
		$arrnums = str_split($nums);
		foreach ($arrnums as $v) {
			$rtn .= $arrnumsTemp[$v];
		}
		return $begin.$rtn;
	}

	function decode($code){

		$begin = substr($code,0,1);
		$rtn = '';
		$len = strpos($this->codelen,$begin);
		if($len!== false){
			$len++;
			$arrnums = str_split(substr($code,-$len));
			foreach ($arrnums as $v) {
				$rtn .= strpos($this->codenums,$v);
			}
		}

		return $rtn;
	}
}

/**** 示例  ****/
$begin = 9950;
$end = $begin + 50;
$obj = new XDeode(9);
for($i=$begin;$i<$end;$i++){
	$en = $obj->encode($i);
	$de = $obj->decode($en);
	echoln("[{$i}]=[{$en}]=[{$de}]");
}

function echoln($str){
	echo "{$str}<br/>";
}
?>

　　运行示例结果：

[9950]=[vmizxPPga]=[9950]
[9951]=[vSNSSPPgk]=[9951]
[9952]=[vNQNyPPgV]=[9952]
[9953]=[vyyJJPPgj]=[9953]
[9954]=[vNzQzPPgq]=[9954]
[9955]=[vyNzmPPgg]=[9955]
[9956]=[vXxSNPPge]=[9956]
[9957]=[vXJJJPPgW]=[9957]
[9958]=[vXziQPPgU]=[9958]
[9959]=[viXxSPPgP]=[9959]
[9960]=[vQxmyPPea]=[9960]
[9961]=[viJyJPPek]=[9961]