added support for Caesar cipher (#4)

* added support for Caesar cipher

binapy/encoding/__init__.py

@@ -4,5 +4,6 @@
 """
 
 from .base64 import *
+from .dumb import *
 from .hex import *
 from .url import *

binapy/encoding/dumb.py

@@ -0,0 +1,69 @@
+"""Implement support for 'dumb' ciphers such as Caesar cipher."""
+
+import string
+from typing import Union
+
+from binapy import binapy_decoder, binapy_encoder
+
+
+@binapy_encoder("caesar")
+def encode_caesar(
+ bp: bytes,
+ shift: int,
+ alphabet: Union[None, str, bytes] = None,
+) -> bytes:
+ """Encode data with Caesar cipher.
+
+ This shifts each character from `bp` by `shift` positions in the given `alphabet`.
+ Characters from `bp` that are not in the alphabet are left as-is.
+ Alphabet is usually `string.ascii_lowercase`, `string.ascii_uppercase`, but you may pass any
+ alphabet, either as a `str` (which will be encoded using 'utf-8'), or as `bytes` directly.
+ By default, alphabet will be auto-detected:
+
+ - `string.ascii_uppercase` if all character from the input are uppercase letters ASCII codes
+ - `string.ascii_lowercase` if all character from the input are lowercase letters ASCII codes
+ - `string.ascii_letters` if all character from the input are letters (both upper and lower case) ASCII codes
+ - the full ASCII range (0-127) if all characters are valid ASCII
+ - the full octect range (0-255) otherwise
+
+ Args:
+ bp: input data.
+ shift: number of places to shift each character in the alphabet.
+ alphabet: alphabet to use. Leave `None` to try to auto-detect alphabet
+
+ Returns:
+ the result of applying Caesar-cipher with `shift` positions to `bp`.
+ """
+ if not alphabet:
+ if all(65 <= c <= 90 for c in bp):
+ alphabet = string.ascii_uppercase
+ elif all(97 <= c <= 122 for c in bp):
+ alphabet = string.ascii_lowercase
+ elif all(65 <= c <= 90 or 97 <= c <= 122 for c in bp):
+ alphabet = string.ascii_letters
+ elif all(0 <= c <= 127 for c in bp):
+ alphabet = bytes(range(128))
+ else:
+ alphabet = bytes(range(256))
+
+ if isinstance(alphabet, str):
+ alphabet = alphabet.encode()
+
+ return bytes(
+ alphabet[(alphabet.index(c) + shift) % len(alphabet)] if c in alphabet else c
+ for c in bp
+ )
+
+
+@binapy_decoder("caesar")
+def decode_caesar(
+ bp: bytes,
+ shift: int,
+ alphabet: Union[None, str, bytes] = None,
+) -> bytes:
+ """Decode data with Caesar cipher.
+
+ Since encoding and decoding are symmetric, this is just an alias to `encode_caesar()` with an
+ opposite shift.
+ """
+ return encode_caesar(bp, -shift, alphabet)

tests/test_encoding.py

@@ -1,3 +1,5 @@
+import string
+
 import pytest
 
 from binapy import BinaPy
@@ -37,3 +39,20 @@ def test_url() -> None:
  bp.encode_to("url", plus_spaces=False)
  == b"https%3A//localhost%3A3200/foo%3Fbar%3Dab%20cd"
  )
+
+
+def test_caesar() -> None:
+ assert BinaPy("caesar13").to("caesar", 13, string.ascii_lowercase) == b"pnrfne13"
+ assert (
+ BinaPy(string.ascii_lowercase).to("caesar", 13, string.ascii_lowercase)
+ == b"nopqrstuvwxyzabcdefghijklm"
+ )
+ assert (
+ BinaPy(string.ascii_letters).to("caesar", 13, string.ascii_letters)
+ == b"nopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklm"
+ )
+
+ for data in (b"caesar", b"CAESAR", b"FooBAR", bytes(range(128))):
+ assert BinaPy(data).to("caesar", 4).decode_from("caesar", 4) == data
+
+ assert BinaPy(b"\x00\xff").to("caesar", 1) == b"\x01\x00"