一个PHP加密解密函数

//加密,十六进制
function str2hex($s)
{
$r = "";
$hexes = array ("0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f");
for ($i=0; $i<strlen($s); $i++)
$r .= ($hexes [(ord($s{$i}) >> 4)] . $hexes [(ord($s{$i}) & 0xf)]);
return $r;
}
//解密,十六进制
function hex2str($s)
{
$r = "";
for ( $i = 0; $i<strlen($s); $i += 2)
{
$x1 = ord($s{$i});
$x1 = ($x1>=48 && $x1<58) ? $x1-48 : $x1-97+10;
$x2 = ord($s{$i+1});
$x2 = ($x2>=48 && $x2<58) ? $x2-48 : $x2-97+10;
$r .= chr((($x1 << 4) & 0xf0) | ($x2 & 0x0f));
}
return $r;
}