[youtube] improved decrypt_signature, closes #1060

youtube_dl/extractor/youtube.py

@@ -179,25 +179,24 @@ class YoutubeIE(InfoExtractor):
     def _decrypt_signature(self, s):
         """Turn the encrypted s field into a working signature"""
 
-        if len(s) == 88:
-            return s[48] + s[81:67:-1] + s[82] + s[66:62:-1] + s[85] + s[61:48:-1] + s[67] + s[47:12:-1] + s[3] + s[11:3:-1] + s[2] + s[12]
-        elif len(s) == 87:
-            return s[62] + s[82:62:-1] + s[83] + s[61:52:-1] + s[0] + s[51:2:-1]
-        elif len(s) == 86:
-            return s[2:63] + s[82] + s[64:82] + s[63]
-        elif len(s) == 85:
-            return s[76] + s[82:76:-1] + s[83] + s[75:60:-1] + s[0] + s[59:50:-1] + s[1] + s[49:2:-1]
-        elif len(s) == 84:
-            return s[83:36:-1] + s[2] + s[35:26:-1] + s[3] + s[25:3:-1] + s[26]
-        elif len(s) == 83:
-            return s[6] + s[3:6] + s[33] + s[7:24] + s[0] + s[25:33] + s[53] + s[34:53] + s[24] + s[54:]
-        elif len(s) == 82:
-            return s[36] + s[79:67:-1] + s[81] + s[66:40:-1] + s[33] + s[39:36:-1] + s[40] + s[35] + s[0] + s[67] + s[32:0:-1] + s[34]
-        elif len(s) == 81:
-            return s[6] + s[3:6] + s[33] + s[7:24] + s[0] + s[25:33] + s[2] + s[34:53] + s[24] + s[54:81]
-
-        else:
-            raise ExtractorError(u'Unable to decrypt signature, key length %d not supported; retrying might work' % (len(s)))
+        def voodoo(a, b):
+            c = a[0];
+            a[0] = a[b % len(a)];
+            a[b] = c;
+            return a;
+
+        s = list(s)
+        s = s[2:len(s)];
+        s = s[::-1];
+        s = s[3:len(s)];
+        s = voodoo(s, 9);
+        s = s[3:len(s)];
+        s = voodoo(s, 43);
+        s = s[3:len(s)];
+        s = s[::-1];
+        s = voodoo(s, 23);
+        s = "".join(s);
+        return s;
 
     def _get_available_subtitles(self, video_id):
         self.report_video_subtitles_download(video_id)