Add VIC cipher codec

README.md

@@ -342,6 +342,7 @@ 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] `vic-keyword-trans1[-trans2]`: aka VIC Cipher
 - [X] `trithemius`: aka Trithemius Cipher (variant of Vigenere Cipher)
 - [X] `vigenere`: aka Vigenere Cipher
 - [X] `xorN`: XOR with a single byte (*N* belongs to [1,255])

docs/pages/enc/crypto.md

@@ -255,8 +255,6 @@ This is a dynamic encoding, that is, it can be called with an integer to define
 'this is a test'
 ```
 
------
-
 ### Trithemius Cipher
 
 This is a variant of the [Vigenere Cipher](#vigenere-cipher) with key `"ABCDEFGHIJKLMNOPQRSTUVWXYZ"`.
@@ -293,6 +291,26 @@ This is a dynamic encoding, that is, it holds the key. There is no default key,
 
 -----
 
+### VIC Cipher
+
+The VIC cipher combines a straddling checkerboard substitution (converting letters to a stream of digits) with a double columnar transposition applied to that digit stream. The checkerboard is built from a keyword-mixed alphabet; single-digit codes are assigned to the 8 letters filling the top row (columns 0–9 minus two blank columns), and two-digit codes to the remaining 18 letters across two lower rows. A keyword and two transposition keys are required.
+
+**Codec** | **Conversions** | **Aliases** | **Comment**
+:---: | :---: | --- | ---
+`vic` | text <-> VIC digit ciphertext | `vic-python-352`, `vic_secret_KEY1_KEY2` | requires checkerboard keyword and at least one transposition key
+
+```python
+>>> import codext
+>>> codext.encode("HELLO", "vic-python-352")
+'42228285'
+>>> codext.decode("42228285", "vic-python-352")
+'HELLO'
+>>> codext.encode("ATTACKATDAWN", "vic-python-352-461")
+'8833231882605277'
+```
+
+-----
+
 ### 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.
@@ -311,4 +329,3 @@ This is a dynamic encoding, that is, it can be called with an integer to define
 >>> codext.encode("~bcy*cy*k*~oy~", "xor-10")
 'this is a test'
 ```
-

src/codext/crypto/__init__.py

@@ -10,6 +10,6 @@
 from .rot import *
 from .scytale import *
 from .shift import *
+from .vic import *
 from .vigenere import *
 from .xor import *
-

src/codext/crypto/vic.py

@@ -0,0 +1,187 @@
+# -*- coding: UTF-8 -*-
+"""VIC Cipher Codec - vic content encoding.
+
+The VIC cipher is a complex manual cipher used by Soviet spies. It combines a
+straddling checkerboard substitution (converting letters to a stream of digits)
+with a double columnar transposition applied to that digit stream.
+
+The straddling checkerboard uses a keyword-mixed alphabet laid out in a 3-row
+grid with two blank positions (default: columns 2 and 6) in the top row.
+Letters in the top row get single-digit codes; letters in the two lower rows
+get two-digit codes whose first digit is the blank-column header, making the
+encoding self-synchronising.
+
+Parameters:
+  keyword   : phrase to build the mixed alphabet for the checkerboard
+  trans1key : first columnar-transposition key (letters or digits)
+  trans2key : second columnar-transposition key (defaults to trans1key)
+
+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/vic-cipher
+"""
+from ..__common__ import *
+
+
+__examples__ = {
+    'enc-dec(vic-python-352)':     ['HELLO', 'ATTACKATDAWN', 'TEST', ''],
+    'enc-dec(vic-python-352-461)': ['HELLO', 'ATTACKATDAWN', 'TEST'],
+}
+__guess__ = []
+
+
+# Positions in the top row (0-9) that are left blank; their values become the
+# row-header digits for the two lower rows of the checkerboard.
+_BLANKS = (2, 6)
+
+
+def _mixed_alpha(keyword):
+    """Return the 26-letter mixed alphabet derived from *keyword*."""
+    seen, result = set(), []
+    for c in keyword.upper():
+        if c.isalpha() and c not in seen:
+            result.append(c)
+            seen.add(c)
+    for c in "ABCDEFGHIJKLMNOPQRSTUVWXYZ":
+        if c not in seen:
+            result.append(c)
+    return result
+
+
+def _build_checkerboard(keyword):
+    """Build encode/decode lookup tables for the straddling checkerboard.
+
+    Layout with blanks=(2,6):
+      col:  0  1  [2]  3  4  5  [6]  7  8  9
+      row0: *  *       *  *  *       *  *  *   (8 single-digit codes)
+      row2: *  *  *    *  *  *  *    *  *  *   (10 two-digit codes 2x)
+      row6: *  *  *    *  *  *  *    *          (8 two-digit codes 6x)
+    """
+    alpha = _mixed_alpha(keyword)
+    b0, b1 = _BLANKS
+    enc, dec, ai = {}, {}, 0
+    # Top row – 8 positions
+    for col in range(10):
+        if col not in _BLANKS:
+            enc[alpha[ai]] = str(col)
+            dec[str(col)] = alpha[ai]
+            ai += 1
+    # Second row – 10 positions, header digit = b0
+    for col in range(10):
+        code = str(b0) + str(col)
+        enc[alpha[ai]] = code
+        dec[code] = alpha[ai]
+        ai += 1
+    # Third row – remaining 8 positions, header digit = b1
+    for col in range(8):          # 26 total – 8 top-row – 10 second-row = 8 remaining
+        code = str(b1) + str(col)
+        enc[alpha[ai]] = code
+        dec[code] = alpha[ai]
+        ai += 1
+    return enc, dec
+
+
+def _col_order(key):
+    """Return column indices sorted by the character value of *key* (stable)."""
+    return [i for _, i in sorted(zip(key, range(len(key))))]
+
+
+def _trans_encode(text, key):
+    """Columnar transposition: write row-by-row, read column-by-column in key order."""
+    k, n = len(key), len(text)
+    if n == 0 or k == 0:
+        return text
+    order = _col_order(key)
+    result = []
+    for col in order:
+        i = col
+        while i < n:
+            result.append(text[i])
+            i += k
+    return ''.join(result)
+
+
+def _trans_decode(text, key):
+    """Reverse columnar transposition."""
+    k, n = len(key), len(text)
+    if n == 0 or k == 0:
+        return text
+    order = _col_order(key)
+    full_rows, remainder = n // k, n % k
+    cols = [None] * k
+    idx = 0
+    for col in order:
+        col_len = full_rows + (1 if col < remainder else 0)
+        cols[col] = list(text[idx:idx + col_len])
+        idx += col_len
+    result = []
+    for row in range(full_rows + (1 if remainder else 0)):
+        for col in range(k):
+            if row < len(cols[col]):
+                result.append(cols[col][row])
+    return ''.join(result)
+
+
+def vic_encode(keyword, trans1, trans2):
+    enc_map, _ = _build_checkerboard(keyword)
+    # The framework converts pure-digit groups to int; convert back to str
+    t1 = str(trans1)
+    t2 = str(trans2) if trans2 else t1
+
+    def encode(text, errors="strict"):
+        _h = handle_error("vic", errors)
+        digits = []
+        for pos, c in enumerate(ensure_str(text).upper()):
+            if c in enc_map:
+                digits.append(enc_map[c])
+            else:
+                digits.append(_h(c, pos, ''.join(digits)))
+        digit_str = ''.join(d for d in digits if d)
+        step1 = _trans_encode(digit_str, t1)
+        step2 = _trans_encode(step1, t2)
+        return step2, len(step2)
+
+    return encode
+
+
+def vic_decode(keyword, trans1, trans2):
+    _, dec_map = _build_checkerboard(keyword)
+    b_set = {str(b) for b in _BLANKS}
+    # The framework converts pure-digit groups to int; convert back to str
+    t1 = str(trans1)
+    t2 = str(trans2) if trans2 else t1
+
+    def decode(text, errors="strict"):
+        _h = handle_error("vic", errors, decode=True)
+        t = ensure_str(text)
+        step1 = _trans_decode(t, t2)
+        digit_str = _trans_decode(step1, t1)
+        result, i = [], 0
+        while i < len(digit_str):
+            d = digit_str[i]
+            if d in b_set:
+                code = digit_str[i:i + 2]
+                if code in dec_map:
+                    result.append(dec_map[code])
+                    i += 2
+                else:
+                    result.append(_h(code, i, ''.join(result)))
+                    i += 2
+            elif d in dec_map:
+                result.append(dec_map[d])
+                i += 1
+            else:
+                result.append(_h(d, i, ''.join(result)))
+                i += 1
+        r = ''.join(c for c in result if c)
+        return r, len(r)
+
+    return decode
+
+
+add("vic", vic_encode, vic_decode,
+    r"^vic[-_]([a-zA-Z]+)[-_]([a-zA-Z0-9]+)(?:[-_]([a-zA-Z0-9]+))?$")