[Help] How to download attachment from octet-stream

[luvyoursmile]

I want to download file 6258.srt from this site. How should I do?
Here is code from header

GET /6258_h4418b97c1f76367e2b5db47b328eee1f_k4.st HTTP/1.1
Host: pl.hdviet.com
User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:29.0) Gecko/20100101 Firefox/29.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://movies.hdviet.com/6.8.4688/jwplayer.flash.swf
Cookie: _ga=GA1.2.1760528871.1397493353; fbm_227923017338590=base_domain=.hdviet.com; H=82cc3aaf86929a786e029f5f1b7f9e443451a9cb963f7ac2f20d3acf8abd4edd7969b3620e6ba8d9bb4908caef49b6bd544fe11490b9eaf8802921a859e899a29b627b5d6be6; __gads=ID=535719ef39a46737:T=1397931316:S=ALNI_MbhbHMdsom1-nlvAYqqw5E9LFMT5g; CR=86cd38a6d3c8c7666c1d9a5f5860b6472f59a5d3963f7ac2a11e36c481a942d32a20fd330833b083ed505e99a008e1b25754a616cbafb6b2dc; oauth_; __utma=121279313.1760528871.1397493353.1398830039.1398830039.1; __utmz=121279313.1398830039.1.1.utmcsr=movies.hdviet.com|utmccn=(referral)|utmcmd=referral|utmcct=/phim-bo-hoat-hinh.html; fbsr_227923017338590=ZGKfWAGCKFDCnTP_hDoRnY6GedboUdvuBochqloLPpA.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; vnhd_sessionhash=toe2tjbei0u1atk77cv2r53fb6
Connection: keep-alive

HTTP/1.1 200 OK
Server: Web HDViet 1.0
Date: Thu, 01 May 2014 16:05:59 GMT
Content-Type: application/octet-stream
Content-Length: 298616
Connection: keep-alive
Content-Disposition: attachment; filename='6258.srt'
Expires: Thu, 01 May 2014 16:05:59 GMT
Cache-Control: max-age=0
Cache-Control: private

Here is content of file 6258.srt, it's encrypted. Help me decrypt
https://app.box.com/s/8zq4rd35reiifs25yr4m


Thanks!