Encryptor.php

<?php
namespace YandexFotkiAPI;

class Encryptor {
	public static function hex2dec($num) {
		$res = '0'; $mul = '1';
		for ($i = strlen($num)-1; $i >= 0; $i--) {
			$res = bcadd($res, bcmul(hexdec($num{$i}), $mul));
			$mul = bcmul($mul, 16);
		}
		return $res;
	}

	public static function dec2hex($num) {
		$ciphers = array('0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F');
		$res = '';
		while ($num != '0') {
			$res = $ciphers[bcmod($num, 16)].$res;
			$num = bcdiv($num, 16, 0);
		}
		return $res;
	}

	public static function str2arr($str) {
		return preg_split('//', $str, -1, PREG_SPLIT_NO_EMPTY);
	}

	public static function encryptPortion($portion, $size, $n, $e) {
		$padding = ($size & 3) ? (4 - ($size & 3)) : 0;
		$padding = (int)($padding/2);

		$plain = '0';
		foreach (array_reverse($portion) as $k => $v)
			$plain = bcadd($plain, bcmul($v, bcpowmod(256, $k, $n)));
		$t = self::dec2hex( bcpowmod($plain, $e, $n) );
		return $t;
	}

	public static function encrypt($key, $data){
		list($nstr, $estr) = explode('#', $key);
		$ps = strlen($nstr);
		$ks = strlen($nstr) / 2;
		$n = self::hex2dec($nstr);
		$e = self::hex2dec($estr);
		$in_size = strlen($data);
		$data = array_map(function($c){return ord($c);}, self::str2arr($data));
		$portion_len = strlen($nstr)/2 - 1;
		$prev_crypted = array_fill(0, $portion_len, 0);
		$out = "";
		while ($in_size) {
			$cur_size = $in_size > $portion_len ? $portion_len : $in_size;
			$portbuf = array();
			for ($i = 0; $i < $cur_size; $i++) $portbuf[$i] = $data[$i] ^ $prev_crypted[$i];
			$encrypted_portion = self::encryptPortion($portbuf, $cur_size, $n, $e);
			$encrypted_size = strlen($encrypted_portion);
			$out .= ($cur_size < 16 ? "0" : "") . dechex($cur_size) . "00";
			$out .= ($ks < 16 ? "0" : "") . dechex($ks) . "00";
			$out .= $encrypted_portion;
			$in_size -= $cur_size;
			for ($i = 0; $i < $encrypted_size; $i += 2)
				$prev_crypted[$i/2] = hexdec('0x'.substr($encrypted_portion, $i, 2));
			$data = array_slice($data, $cur_size);
		}
		return base64_encode(pack("H*", $out));
	}
}