Added codec: vernam

Author: dhondta

README.md

@@ -383,6 +383,7 @@ This category also contains `ascii85`, `adobe`, `[x]btoa`, `zeromq` with the `ba
 - [X] `skip`: aka Skip Cipher (transposition reading every N-th character, looping on the text)
 - [X] `trithemius`: aka Trithemius Cipher (variant of Vigenere Cipher)
 - [X] `twosquare`: aka Two-square Cipher or Double Playfair (bigrams substituted with two keyed squares, vertically or horizontally)
+- [X] `vernam`: aka Vernam Cipher (XOR with a repeating key)
 - [X] `vic`: aka VIC Cipher
 - [X] `vigenere`: aka Vigenere Cipher
 - [X] `xorN`: XOR with a single byte (*N* belongs to [1,255])

docs/pages/enc/crypto.md

@@ -759,6 +759,23 @@ Alphabet markers:
 
 -----
 
+### Vernam Cipher
+
+This is a dynamic encoding, that is, it holds the key. Each character of the text is XORed with the corresponding character of the repeated key ; with a random key as long as the text, used only once, it becomes the one-time pad. As XOR is its own inverse, decoding is the same as encoding. There is no default key, meaning that `vernam` as the encoding scheme throws a `LookupError` indicating that the _key must be a non-empty string_.
+
+**Codec** | **Conversions** | **Aliases** | **Comment**
+:---: | :---: | --- | ---
+`vernam` | text <-> Vernam ciphertext | `vernam-key`, `vernam_cipher-My Secret!` | key is case-sensitive and may hold any character
+
+```python
+>>> codext.encode("this is a test", "vernam-key")
+'\x1f\r\x10\x18E\x10\x18E\x18K\x11\x1c\x18\x11'
+>>> codext.decode("\x1f\r\x10\x18E\x10\x18E\x18K\x11\x1c\x18\x11", "vernam-key")
+'this is a test'
+```
+
+-----
+
 ### 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_.

src/codext/crypto/__init__.py

@@ -32,5 +32,6 @@
 from .skip import *
 from .twosquare import *
 from .vic import *
+from .vernam import *
 from .vigenere import *
 from .xor import *

src/codext/crypto/vernam.py

@@ -0,0 +1,39 @@
+# -*- coding: UTF-8 -*-
+"""Vernam Cipher Codec - vernam content encoding.
+
+The Vernam cipher, patented by Gilbert Vernam in 1919, XORs each character of the text with the corresponding character
+ of a repeated key ; with a random key as long as the text, used only once, it becomes the one-time pad. As XOR is its
+ own inverse, decoding is the same as 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)
+
+Reference: https://en.wikipedia.org/wiki/Gilbert_Vernam
+"""
+from ..__common__ import *
+
+
+__examples__ = {
+    'enc(vernam|vernam-cipher)': None,
+    'enc(vernam-key)':           {'this is a test': "\x1f\r\x10\x18E\x10\x18E\x18K\x11\x1c\x18\x11"},
+    'enc(vernam_cipher-Key)':    {'this is a test': "?\r\x108E\x108E\x18k\x11\x1c8\x11"},
+    'dec(vernam-key)':           {"\x1f\r\x10\x18E\x10\x18E\x18K\x11\x1c\x18\x11": 'this is a test'},
+    'enc-dec(vernam-secret|vernam-a b!)': ["", "this is a test", "@random{256}", "Caf\xe9 €"],
+}
+__guess__ = ["vernam-key", "vernam-password", "vernam-secret"]
+
+
+def vernam(key=None):
+    def code(text, errors="strict"):
+        if not key:
+            raise LookupError("Bad parameter for encoding 'vernam': key must be a non-empty string")
+        r = "".join(chr(ord(c) ^ ord(key[i % len(key)])) for i, c in enumerate(ensure_str(text)))
+        return r, len(r)
+    return code
+
+
+add("vernam", vernam, vernam, r"^vernam(?:[-_]cipher)?(?:[-_](.+))?$", examples=__examples__, guess=__guess__,
+    transitive=True, penalty=.1)