phpass在encode64()中使用了一种我不太熟悉的算法来进行base 64编码。而Base64和Uuencode是将6个比特位成组线性拆分来生成每个8位字节,然后映射到可打印字符。而encode64
则会重新排列这些比特位:
input bit location: abcdefgh ijklmnop qrstuvwx
base64 bit location: ..abcdef ..ghijkl ..mnopqr ..stuvwx
encode64 bit location: ..cdefgh ..mnopab ..wxijkl ..qrstuv
这个算法是否广为人知?除了向后兼容之外,为什么选择它而不是Base64?以下是我重写后的内容以澄清该算法:
function encode64($input, $bytesToProcess)
{
// convert to array of ints
for ($i = 0; $i < $bytesToProcess; $i++) {
$bytes[] = ord($input[$i]);
}
$octets = array();
$i = 0;
do {
$value = $bytes[$i++];
$octets[] = $value & 0x3f;
if ($i < $bytesToProcess) {
$value |= $bytes[$i] << 8;
}
$octets[] = ($value >> 6) & 0x3f;
if ($i++ >= $bytesToProcess) {
break;
}
if ($i < $bytesToProcess) {
$value |= $bytes[$i] << 16;
}
$octets[] = ($value >> 12) & 0x3f;
if ($i++ >= $bytesToProcess) {
break;
}
$octets[] = ($value >> 18) & 0x3f;
} while ($i < $bytesToProcess);
return array_map(function ($i) {
return str_pad(base_convert($i, 10, 2), 6, '0', STR_PAD_LEFT);
}, $octets);
}
var_export(encode64("Man", 3));
(更新以指明每个输入位移动的确切位置)