221 lines
7.1 KiB
Python
221 lines
7.1 KiB
Python
from itertools import izip
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DEFAULT_PAD_WIDTH = 72
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def mod25encode(msg, pad):
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mod25 = Mod25(pad=pad)
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return mod25.encode(msg)
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def mod25decode(msg, pad):
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mod25 = Mod25(pad=pad)
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return mod25.decode(msg)
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class Mod25(object):
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_pad_modulo = 3
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_padline_offset = -2
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_textline_offset = -1
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_cipher_floor = 1
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_cipher_ceil = 25
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_nullchar = '.'
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def __init__(self, pad=''):
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self.pad = pad
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self._as_alpha = {}
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self._as_nums = {}
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self._mk_as_alpha_as_nums()
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def _mk_as_alpha_as_nums(self):
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as_alpha = {}
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as_nums = {}
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a_chr = ord('A')
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past_j = False
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for char in range(self._cipher_ceil + 1):
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letter = chr(a_chr + char)
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if letter != 'J':
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key = char + (1 if not past_j else 0)
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as_alpha[key] = letter
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else:
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past_j = True
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for key, val in as_alpha.iteritems():
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as_nums[val] = key
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self._as_alpha.update(as_alpha)
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self._as_nums.update(as_nums)
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def encode(self, msg):
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ret = []
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filled = list(self._text_padfill(msg))
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for i, line in enumerate(self._text_cipherfill(filled)):
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lineno = i + 1
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if self._is_cipherline(lineno):
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ret.append(line)
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return ''.join(ret).strip(self._nullchar)
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def decode(self, ciphertext):
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ret = []
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filled = list(self._cipher_padfill(ciphertext))
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for i, line in enumerate(self._cipher_textfill(filled)):
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lineno = i + 1
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if self._is_textline(lineno):
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ret.append(line)
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return ''.join(ret).strip(self._nullchar)
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def create_pad(self, length, width=DEFAULT_PAD_WIDTH):
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return '\n'.join(self.create_pad_lines(length, width=width))
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def create_pad_lines(self, length, width=DEFAULT_PAD_WIDTH):
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chars = self._create_chars_for_pad(length)
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lines = _chunk_chars_into_lines(chars, self._nullchar, width=width)
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for line in lines:
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yield line
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yield ''
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yield ''
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def _create_chars_for_pad(self, length):
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chars = []
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for char in range(length):
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chars.append(self._as_alpha[_get_randint(self._cipher_ceil)])
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return ''.join(chars)
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def _ensure_pad_is_lines(self):
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if isinstance(self.pad, basestring):
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self.pad = self.pad.splitlines()
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def _text_padfill(self, text):
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self._ensure_pad_is_lines()
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padlines = [line.strip() for line in self.pad if line.strip()]
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textlines = _chunk_chars_into_lines(text, self._nullchar,
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_get_textwidth(padlines))
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for textline, padline in izip(textlines, padlines):
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yield padline
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yield textline
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yield ''
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def _cipher_padfill(self, ciphertext):
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self._ensure_pad_is_lines()
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padlines = [line.strip() for line in self.pad if line.strip()]
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cipherlines = _chunk_chars_into_lines(ciphertext, self._nullchar,
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_get_textwidth(padlines))
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for cipherline, padline in izip(cipherlines, padlines):
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yield padline
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yield ''
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yield cipherline
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def _text_cipherfill(self, padfilled_text_lines):
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for i, line in enumerate(padfilled_text_lines):
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lineno = i + 1
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if self._is_cipherline(lineno):
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padline = padfilled_text_lines[i - abs(self._padline_offset)]
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textline = padfilled_text_lines[i - abs(self._textline_offset)]
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yield padline
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yield textline
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yield self._cipherline_from_padline_and_textline(padline,
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textline)
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def _cipher_textfill(self, padfilled_cipher_lines):
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for i, line in enumerate(padfilled_cipher_lines):
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lineno = i + 1
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if self._is_cipherline(lineno):
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padline = padfilled_cipher_lines[i - abs(self._padline_offset)]
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textline = \
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padfilled_cipher_lines[i - abs(self._textline_offset)]
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yield padline
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yield self._textline_from_cipherline_and_padline(line, padline)
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yield line
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def _cipherline_from_padline_and_textline(self, padline, textline):
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ret = []
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for padchar, textchar in izip(padline, textline):
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if textchar == self._nullchar:
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ret.append(self._nullchar)
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continue
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charnum = self._as_nums[padchar] + self._as_nums[textchar]
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idx = charnum if charnum <= self._cipher_ceil else \
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charnum % self._cipher_ceil
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ret.append(self._as_alpha[idx])
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return ''.join(ret)
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def _textline_from_cipherline_and_padline(self, cipherline, padline):
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ret = []
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for ciphercar, padchar in izip(cipherline, padline):
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if ciphercar == self._nullchar:
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ret.append(self._nullchar)
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continue
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charnum = self._as_nums[ciphercar] - self._as_nums[padchar]
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idx = charnum if charnum <= self._cipher_ceil else \
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charnum % self._cipher_ceil
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if idx < 0:
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idx = self._cipher_ceil + idx
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ret.append(self._as_alpha[idx])
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return ''.join(ret)
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def _is_padline(self, lineno):
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return self._is_cipherline(lineno + abs(self._padline_offset))
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def _is_textline(self, lineno):
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return self._is_cipherline(lineno + abs(self._textline_offset))
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def _is_cipherline(self, lineno):
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return not lineno % self._pad_modulo
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def _chunk_chars_into_lines(chars, nullchar, width=DEFAULT_PAD_WIDTH):
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lines = []
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for chunk in _as_line_chunks(chars, nullchar, width=width):
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lines.append(chunk)
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return lines
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def _as_line_chunks(chars, nullchar, width=DEFAULT_PAD_WIDTH):
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chunk = []
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for char in chars.replace('\n', ''):
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chunk.append(char)
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if len(chunk) == width:
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yield ''.join(chunk)
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chunk = []
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if len(chunk) < width:
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chunk += ([nullchar] * (width - len(chunk)))
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yield ''.join(chunk)
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def _get_textwidth(textlines):
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return max([len(line) for line in textlines])
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def _get_randint(modulo, randomness_file='/dev/urandom',
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fallback_to_fake=True):
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if not _DEV_URANDOM.get('fp'):
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_get_urandom_fp(randomness_file=randomness_file,
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fallback_to_fake=fallback_to_fake)
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ret = ord(_DEV_URANDOM['fp'].read(1)) % modulo
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return ret if ret != 0 else _get_randint(modulo)
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class _FakeDevUrandom(object):
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@staticmethod
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def read(nchars):
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import random
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ret = []
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for i in range(0, nchars):
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ret.append(chr(random.randint(0, 255)))
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return ''.join(ret)
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def _get_urandom_fp(randomness_file='/dev/urandom', fallback_to_fake=True):
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try:
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_DEV_URANDOM['fp'] = open(randomness_file)
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except (OSError, IOError):
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if fallback_to_fake:
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_DEV_URANDOM['fp'] = _FakeDevUrandom()
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else:
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raise
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_DEV_URANDOM = {}
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