Add Phillips cipher codec

Co-authored-by: dhondta <9108102+dhondta@users.noreply.github.com>
Agent-Logs-Url: https://github.com/dhondta/python-codext/sessions/01837063-2248-4979-b695-b34e3bf223bf

Author: Copilot

README.md

@@ -286,6 +286,7 @@ This category also contains `ascii85`, `adobe`, `[x]btoa`, `zeromq` with the `ba
 - [X] `barbie-N`: aka Barbie Typewriter (*N* belongs to [1, 4])
 - [X] `beaufort`: aka Beaufort Cipher (variant of Vigenere Cipher)
 - [X] `citrix`: aka Citrix CTX1 password encoding
+- [X] `phillips`: aka Phillips Cipher (polyalphabetic block cipher with 8 key squares)
 - [X] `polybius`: aka Polybius Square Cipher
 - [X] `railfence`: aka Rail Fence Cipher
 - [X] `rotN`: aka Caesar cipher (*N* belongs to [1,25])

src/codext/crypto/__init__.py

@@ -4,6 +4,7 @@
 from .bacon import *
 from .barbie import *
 from .citrix import *
+from .phillips import *
 from .polybius import *
 from .railfence import *
 from .rot import *

src/codext/crypto/phillips.py

@@ -0,0 +1,142 @@
+# -*- coding: UTF-8 -*-
+"""Phillips Cipher Codec - phillips content encoding.
+
+The Phillips cipher is a polyalphabetic substitution cipher using 8 key
+squares.  The first square is a 5×5 grid built from a keyword (I and J share
+one cell).  Seven additional squares are derived by rotating every row of the
+previous square one step to the left.  Plaintext is enciphered in bigrams,
+each pair using the next square in a cycle of 8.  Non-alphabetic characters
+are passed through unchanged; J is treated as I.
+
+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/phillips-cipher
+"""
+from ..__common__ import *
+
+_ALPHA = "ABCDEFGHIKLMNOPQRSTUVWXYZ"  # 25 letters; I and J share one cell
+_ALPHA_SET = set(_ALPHA)
+
+
+__examples__ = {
+    'enc(phillips)':             None,
+    'enc(phillips-key)':         {'ATTACK': 'BSSBIC', 'TESTME': 'QBTPLY', 'ABCDEF': 'BKDFYD'},
+    'enc-dec(phillips-key)':     ['ATTACK', 'TESTME', 'ABCDEF'],
+    'enc-dec(phillips-secret)':  ['HELLOWORLD', 'ATTACKATDAWN'],
+}
+__guess__ = ["phillips-key", "phillips-secret", "phillips-password"]
+
+
+def _build_grid(key):
+    """Build the initial 5×5 grid from a keyword (J treated as I)."""
+    seen, letters = set(), []
+    for c in key.upper().replace("J", "I") + _ALPHA:
+        if c in _ALPHA_SET and c not in seen:
+            letters.append(c)
+            seen.add(c)
+    return [letters[i * 5:(i + 1) * 5] for i in range(5)]
+
+
+def _make_grids(key):
+    """Return all 8 grids: the initial grid plus 7 row-rotated variants."""
+    grid = _build_grid(key)
+    grids = [grid]
+    for _ in range(7):
+        grid = [row[1:] + [row[0]] for row in grid]
+        grids.append(grid)
+    return grids
+
+
+def _grid_positions(grid):
+    """Return a mapping from letter to (row, col) for the given grid."""
+    return {ch: (r, c) for r, row in enumerate(grid) for c, ch in enumerate(row)}
+
+
+def _process_pair(a, b, grid, decode=False):
+    """Encode or decode a letter pair using Playfair substitution rules.
+
+    Same row   → each letter shifts one step right (encode) / left (decode).
+    Same col   → each letter shifts one step down  (encode) / up   (decode).
+    Rectangle  → each letter moves to the other's column (self-inverse).
+    """
+    pos = _grid_positions(grid)
+    r1, c1 = pos[a]
+    r2, c2 = pos[b]
+    d = -1 if decode else 1
+    if r1 == r2:
+        return grid[r1][(c1 + d) % 5], grid[r2][(c2 + d) % 5]
+    if c1 == c2:
+        return grid[(r1 + d) % 5][c1], grid[(r2 + d) % 5][c2]
+    return grid[r1][c2], grid[r2][c1]  # rectangle rule is its own inverse
+
+
+def phillips_encode(key):
+    _key = (key or "").strip()
+    # Compute grids eagerly if key is valid; otherwise defer error to call time
+    _grids = _make_grids(_key) if _key and _key.isalpha() else None
+
+    def encode(text, errors="strict"):
+        if _grids is None:
+            raise LookupError("Bad parameter for encoding 'phillips': "
+                              "key must be a non-empty alphabetic string")
+        t = ensure_str(text).upper().replace("J", "I")
+        alpha = [(i, c) for i, c in enumerate(t) if c in _ALPHA_SET]
+        # Pad to an even count with a trailing X
+        padding_char = None
+        if len(alpha) % 2 == 1:
+            alpha.append((-1, "X"))
+        enc_map = {}
+        for pair_num, k in enumerate(range(0, len(alpha), 2)):
+            pos1, a = alpha[k]
+            pos2, b = alpha[k + 1]
+            e1, e2 = _process_pair(a, b, _grids[pair_num % 8])
+            enc_map[pos1] = e1
+            if pos2 >= 0:
+                enc_map[pos2] = e2
+            else:
+                padding_char = e2
+        result = [enc_map.get(i, c) for i, c in enumerate(t)]
+        if padding_char is not None:
+            result.append(padding_char)
+        r = "".join(result)
+        return r, len(text)
+
+    return encode
+
+
+def phillips_decode(key):
+    _key = (key or "").strip()
+    # Compute grids eagerly if key is valid; otherwise defer error to call time
+    _grids = _make_grids(_key) if _key and _key.isalpha() else None
+
+    def decode(text, errors="strict"):
+        if _grids is None:
+            raise LookupError("Bad parameter for decoding 'phillips': "
+                              "key must be a non-empty alphabetic string")
+        t = ensure_str(text).upper().replace("J", "I")
+        alpha = [(i, c) for i, c in enumerate(t) if c in _ALPHA_SET]
+        if len(alpha) % 2 == 1:
+            if errors == "strict":
+                raise ValueError("phillips: encoded text must contain an even "
+                                 "number of alphabetic characters")
+            alpha = alpha[:-1]
+        dec_map = {}
+        for pair_num, k in enumerate(range(0, len(alpha), 2)):
+            pos1, a = alpha[k]
+            pos2, b = alpha[k + 1]
+            d1, d2 = _process_pair(a, b, _grids[pair_num % 8], decode=True)
+            dec_map[pos1] = d1
+            dec_map[pos2] = d2
+        result = [dec_map.get(i, c) for i, c in enumerate(t)]
+        r = "".join(result)
+        return r, len(text)
+
+    return decode
+
+
+add("phillips", phillips_encode, phillips_decode,
+    r"^phillips(?:[-_]cipher)?(?:[-_]([a-zA-Z]+))?$", penalty=.1)