[utils] Add generic caesar cipher and rot47

test/test_utils.py

@@ -19,6 +19,7 @@ from youtube_dl.utils import (
     age_restricted,
     args_to_str,
     encode_base_n,
+    caesar,
     clean_html,
     date_from_str,
     DateRange,
@@ -69,6 +70,7 @@ from youtube_dl.utils import (
     remove_start,
     remove_end,
     remove_quotes,
+    rot47,
     shell_quote,
     smuggle_url,
     str_to_int,
@@ -1369,6 +1371,20 @@ Line 1
         self.assertRaises(ValueError, encode_base_n, 0, 70)
         self.assertRaises(ValueError, encode_base_n, 0, 60, custom_table)
 
+    def test_caesar(self):
+        self.assertEqual(caesar('ace', 'abcdef', 2), 'cea')
+        self.assertEqual(caesar('cea', 'abcdef', -2), 'ace')
+        self.assertEqual(caesar('ace', 'abcdef', -2), 'eac')
+        self.assertEqual(caesar('eac', 'abcdef', 2), 'ace')
+        self.assertEqual(caesar('ace', 'abcdef', 0), 'ace')
+        self.assertEqual(caesar('xyz', 'abcdef', 2), 'xyz')
+        self.assertEqual(caesar('abc', 'acegik', 2), 'ebg')
+        self.assertEqual(caesar('ebg', 'acegik', -2), 'abc')
+
+    def test_rot47(self):
+        self.assertEqual(rot47('youtube-dl'), r'J@FEF36\5=')
+        self.assertEqual(rot47('YOUTUBE-DL'), r'*~&%&qt\s{')
+
     def test_urshift(self):
         self.assertEqual(urshift(3, 1), 1)
         self.assertEqual(urshift(-3, 1), 2147483646)

youtube_dl/utils.py

@@ -5383,6 +5383,19 @@ def decode_packed_codes(code):
         obfucasted_code)
 
 
+def caesar(s, alphabet, shift):
+    if shift == 0:
+        return s
+    l = len(alphabet)
+    return ''.join(
+        alphabet[(alphabet.index(c) + shift) % l] if c in alphabet else c
+        for c in s)
+
+
+def rot47(s):
+    return caesar(s, r'''!"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~''', 47)
+
+
 def parse_m3u8_attributes(attrib):
     info = {}
     for (key, val) in re.findall(r'(?P<key>[A-Z0-9-]+)=(?P<val>"[^"]+"|[^",]+)(?:,|$)', attrib):