Add Beaufort cipher codec

src/codext/crypto/__init__.py

@@ -1,6 +1,7 @@
 # -*- coding: UTF-8 -*-
 from .affine import *
 from .atbash import *
+from .beaufort import *
 from .bacon import *
 from .barbie import *
 from .citrix import *

src/codext/crypto/beaufort.py

@@ -0,0 +1,62 @@
+# -*- coding: UTF-8 -*-
+"""Beaufort Cipher Codec - beaufort content encoding.
+
+The Beaufort cipher is a polyalphabetic substitution cipher similar to the
+Vigenère cipher, but based on a different operation: instead of adding the key
+to the plaintext, the plaintext is subtracted from the key (C = K - P mod 26).
+This makes the cipher self-reciprocal: the same operation is used for both
+encoding and decoding.
+
+This codec:
+- en/decodes strings from str to str
+- en/decodes strings from bytes to bytes
+- decodes file content to str (read)
+- encodes file content from str to bytes (write)
+
+Reference: https://www.dcode.fr/beaufort-cipher
+"""
+from string import ascii_lowercase as LC, ascii_uppercase as UC
+
+from ..__common__ import *
+
+
+__examples__ = {
+    'enc(beaufort)':              None,
+    'enc(beaufort-lemon)':        {'ATTACKATDAWN': 'LLTOLBETLNPR'},
+    'enc(beaufort-key)':          {'hello': 'danzq'},
+    'enc(beaufort_key)':          {'Hello World': 'Danzq Cwnnh'},
+    'enc-dec(beaufort-secret)':   ['hello world', 'ATTACK AT DAWN', 'Test 1234!'],
+}
+__guess__ = ["beaufort-key", "beaufort-secret", "beaufort-password"]
+
+
+__char = lambda c, k, i: (LC if (b := c in LC) else UC)[(ord(k[i % len(k)]) - ord('a') - \
+                                                          (ord(c) - ord("Aa"[b]))) % 26]
+
+
+def __check(key):
+    key = key.lower()
+    if not key or not key.isalpha():
+        raise LookupError("Bad parameter for encoding 'beaufort': key must be a non-empty alphabetic string")
+    return key
+
+
+def beaufort_encode(key):
+    def encode(text, errors="strict"):
+        result, i, k = [], 0, __check(key)
+        for c in ensure_str(text):
+            if c in LC or c in UC:
+                result.append(__char(c, k, i))
+                i += 1
+            else:
+                result.append(c)
+        r = "".join(result)
+        return r, len(r)
+    return encode
+
+
+# Beaufort is self-reciprocal: decoding uses the same operation as encoding
+beaufort_decode = beaufort_encode
+
+
+add("beaufort", beaufort_encode, beaufort_decode, r"beaufort(?:[-_]cipher)?(?:[-_]([a-zA-Z]+))?$", penalty=.1)