Add Playfair cipher codec

README.md

@@ -290,6 +290,7 @@ This category also contains `ascii85`, `adobe`, `[x]btoa`, `zeromq` with the `ba
 - [X] `rotN`: aka Caesar cipher (*N* belongs to [1,25])
 - [X] `scytaleN`: encrypts using the number of letters on the rod (*N* belongs to [1,[)
 - [X] `shiftN`: shift ordinals (*N* belongs to [1,255])
+- [X] `vigenere`: aka Vigenere Cipher
 - [X] `xorN`: XOR with a single byte (*N* belongs to [1,255])
 
 > :warning: Crypto functions are of course definitely **NOT** encoding functions ; they are implemented for leveraging the `.encode(...)` API from `codecs`.

docs/pages/enc/crypto.md

@@ -202,6 +202,24 @@ This is a dynamic encoding, that is, it can be called with an integer to define
 
 -----
 
+### Vigenere Cipher
+
+This is a dynamic encoding, that is, it holds the key. There is no default key, meaning that `vigenere` as the encoding scheme throws a `LookupError` indicating that the _key must be a non-empty alphabetic string_.
+
+**Codec** | **Conversions** | **Aliases** | **Comment**
+:---: | :---: | --- | ---
+`vigenere` | text <-> Vigenere ciphertext | `vigenere-abcdef`, `vigenere_MySuperSecret` | key only consists of characters, not digits
+
+```python
+>>> codext.encode("This is a test !", "vigenere-abababa")
+'Tiit it a tfsu !'
+>>> codext.encode("This is a test !", "vigenere_MySuperSecret")
+'Ffam xw r liuk !'
+>>> codext.decode("Tiit it a tfsu !", "vigenere-abababa")
+```
+
+-----
+
 ### XOR with 1 byte
 
 This is a dynamic encoding, that is, it can be called with an integer to define the ordinal of the byte to XOR with the input text.

src/codext/crypto/__init__.py

@@ -4,10 +4,12 @@
 from .bacon import *
 from .barbie import *
 from .citrix import *
+from .playfair import *
 from .polybius import *
 from .railfence import *
 from .rot import *
 from .scytale import *
 from .shift import *
+from .vigenere import *
 from .xor import *
 

src/codext/crypto/playfair.py

@@ -0,0 +1,138 @@
+# -*- coding: UTF-8 -*-
+"""Playfair Cipher Codec - playfair content encoding.
+
+The Playfair cipher is a symmetric encryption method using polygram substitution
+with bigrams (pairs of letters), invented in 1854 by Charles Wheatstone, but
+popularized by his friend Lord Playfair.
+
+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/playfair-cipher
+"""
+from ..__common__ import *
+
+
+__examples__ = {
+    # Classic example from Wikipedia (key "PLAYFAIR EXAMPLE"):
+    #   the EE in "TREE" is split with an X filler during encoding, so decoding
+    #   exposes the filler: "TREESTUMP" → encoded → decoded as "TREXESTUMP"
+    'enc(playfair-playfairexample)': {'HIDETHEGOLDINTHETREESTUMP': 'BMODZBXDNABEKUDMUIXMMOUVIF'},
+    'dec(playfair-playfairexample)': {'BMODZBXDNABEKUDMUIXMMOUVIF': 'HIDETHEGOLDINTHETREXESTUMP'},
+    'enc-dec(playfair-keyword)':     ['INSTRUMENT'],
+}
+__guess__ = ["playfair"]
+
+
+# Standard 5×5 Playfair alphabet (I and J share the same cell)
+_DEFAULT_ALPHABET = "ABCDEFGHIKLMNOPQRSTUVWXYZ"
+
+
+def _build_grid(key=None):
+    """Build the 5×5 Playfair grid from an optional keyword."""
+    seen, grid = set(), []
+    if key:
+        for c in key.upper():
+            if c == 'J':
+                c = 'I'
+            if c.isalpha() and c not in seen:
+                seen.add(c)
+                grid.append(c)
+    for c in _DEFAULT_ALPHABET:
+        if c not in seen:
+            seen.add(c)
+            grid.append(c)
+    pos = {grid[i]: (i // 5, i % 5) for i in range(25)}
+    return grid, pos
+
+
+def _filler(c):
+    """Return the filler character for a given letter (X, or Q when the letter is X)."""
+    return 'Q' if c == 'X' else 'X'
+
+
+def _make_bigrams(text):
+    """Convert plaintext to bigrams, inserting fillers for repeated-letter pairs."""
+    chars = []
+    for c in ensure_str(text).upper():
+        if c == 'J':
+            chars.append('I')
+        elif c.isalpha():
+            chars.append(c)
+    bigrams = []
+    i = 0
+    while i < len(chars):
+        a = chars[i]
+        if i + 1 < len(chars):
+            b = chars[i + 1]
+            if a == b:
+                bigrams.append((a, _filler(a)))
+                i += 1
+            else:
+                bigrams.append((a, b))
+                i += 2
+        else:
+            bigrams.append((a, _filler(a)))
+            i += 1
+    return bigrams
+
+
+def _encode_bigram(grid, pos, a, b):
+    r_a, c_a = pos[a]
+    r_b, c_b = pos[b]
+    if r_a == r_b:
+        return grid[r_a * 5 + (c_a + 1) % 5], grid[r_b * 5 + (c_b + 1) % 5]
+    elif c_a == c_b:
+        return grid[((r_a + 1) % 5) * 5 + c_a], grid[((r_b + 1) % 5) * 5 + c_b]
+    else:
+        return grid[r_a * 5 + c_b], grid[r_b * 5 + c_a]
+
+
+def _decode_bigram(grid, pos, a, b):
+    r_a, c_a = pos[a]
+    r_b, c_b = pos[b]
+    if r_a == r_b:
+        return grid[r_a * 5 + (c_a - 1) % 5], grid[r_b * 5 + (c_b - 1) % 5]
+    elif c_a == c_b:
+        return grid[((r_a - 1) % 5) * 5 + c_a], grid[((r_b - 1) % 5) * 5 + c_b]
+    else:
+        return grid[r_a * 5 + c_b], grid[r_b * 5 + c_a]
+
+
+def playfair_encode(key=None):
+    grid, pos = _build_grid(key)
+    def encode(text, errors="strict"):
+        t = ensure_str(text)
+        result = []
+        for a, b in _make_bigrams(t):
+            ea, eb = _encode_bigram(grid, pos, a, b)
+            result.extend([ea, eb])
+        r = "".join(result)
+        return r, len(t)
+    return encode
+
+
+def playfair_decode(key=None):
+    grid, pos = _build_grid(key)
+    def decode(text, errors="strict"):
+        t = ensure_str(text)
+        chars = []
+        for c in t.upper():
+            if c == 'J':
+                chars.append('I')
+            elif c.isalpha():
+                chars.append(c)
+        result = []
+        for i in range(0, len(chars) - 1, 2):
+            da, db = _decode_bigram(grid, pos, chars[i], chars[i + 1])
+            result.extend([da, db])
+        r = "".join(result)
+        return r, len(t)
+    return decode
+
+
+add("playfair", playfair_encode, playfair_decode, r"^playfair(?:[-_]cipher)?(?:[-_]([a-zA-Z]+))?$",
+    printables_rate=1.)

src/codext/crypto/vigenere.py

@@ -0,0 +1,65 @@
+# -*- coding: UTF-8 -*-
+"""Vigenere Cipher Codec - vigenere content encoding.
+
+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)
+"""
+from string import ascii_lowercase as LC, ascii_uppercase as UC
+
+from ..__common__ import *
+
+
+__examples__ = {
+    'enc(vigenere)':             None,
+    'enc(vigenere-lemon)':       {'ATTACKATDAWN': 'LXFOPVEFRNHR'},
+    'enc(vigenere-key)':         {'hello': 'rijvs'},
+    'enc(vigenère_key)':         {'Hello World': 'Rijvs Uyvjn'},
+    'enc-dec(vigenere-secret)':  ['hello world', 'ATTACK AT DAWN', 'Test 1234!'],
+}
+__guess__ = ["vigenere-key", "vigenere-secret", "vigenere-password"]
+
+
+__char = lambda c, k, i, d=False: (LC if (b := c in LC) else UC)[(ord(c) - ord("Aa"[b]) + \
+                                                                  [1, -1][d] * (ord(k[i % len(k)]) - ord('a'))) % 26]
+
+
+def __check(key):
+    key = key.lower()
+    if not key or not key.isalpha():
+        raise LookupError("Bad parameter for encoding 'vigenere': key must be a non-empty alphabetic string")
+    return key
+
+
+def vigenere_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
+
+
+def vigenere_decode(key):
+    def decode(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, True))
+                i += 1
+            else:
+                result.append(c)
+        r = "".join(result)
+        return r, len(r)
+    return decode
+
+
+add("vigenere", vigenere_encode, vigenere_decode, r"vigen[eè]re(?:[-_]cipher)?(?:[-_]([a-zA-Z]+))?$", penalty=.1)
+