python - 对于 Kasiski 测试，如何在 Python 中实现 26x26 表

Question

这是表格http://en.wikipedia.org/wiki/File:Vigen%C3%A8re_square_shading.svg

如何在 Python 中实现这个表？这样做的方法是什么？

以及有关如何检查例如 Row: L & Column G 的任何线索都成为 R 欢迎。

Answer 1

>>> letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
>>> mat = [(letters * 2)[i:i+26] for i in range(26)]
>>> print '\n'.join(mat)
ABCDEFGHIJKLMNOPQRSTUVWXYZ
BCDEFGHIJKLMNOPQRSTUVWXYZA
CDEFGHIJKLMNOPQRSTUVWXYZAB
DEFGHIJKLMNOPQRSTUVWXYZABC
EFGHIJKLMNOPQRSTUVWXYZABCD
FGHIJKLMNOPQRSTUVWXYZABCDE
GHIJKLMNOPQRSTUVWXYZABCDEF
HIJKLMNOPQRSTUVWXYZABCDEFG
IJKLMNOPQRSTUVWXYZABCDEFGH
JKLMNOPQRSTUVWXYZABCDEFGHI
KLMNOPQRSTUVWXYZABCDEFGHIJ
LMNOPQRSTUVWXYZABCDEFGHIJK
MNOPQRSTUVWXYZABCDEFGHIJKL
NOPQRSTUVWXYZABCDEFGHIJKLM
OPQRSTUVWXYZABCDEFGHIJKLMN
PQRSTUVWXYZABCDEFGHIJKLMNO
QRSTUVWXYZABCDEFGHIJKLMNOP
RSTUVWXYZABCDEFGHIJKLMNOPQ
STUVWXYZABCDEFGHIJKLMNOPQR
TUVWXYZABCDEFGHIJKLMNOPQRS
UVWXYZABCDEFGHIJKLMNOPQRST
VWXYZABCDEFGHIJKLMNOPQRSTU
WXYZABCDEFGHIJKLMNOPQRSTUV
XYZABCDEFGHIJKLMNOPQRSTUVW
YZABCDEFGHIJKLMNOPQRSTUVWX
ZABCDEFGHIJKLMNOPQRSTUVWXY

或者，您可以即时计算元素：

def get_elem(row, col):
  return 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'[(ord(row) + ord(col)) % 26]

print get_elem('L', 'G')

Answer 2

我喜欢尽可能使用标准库，以避免滚动我自己的代码并无意中遗漏一些东西（比如不小心放错地方或忘记了一个字母。）

import string
import collections

def vigsquare(printable=False):
    '''
    Returns a string like a vigenere square,
    printable joins each row with a newline so it's literally square
    printable=False (defaul) joins without newlines for easier 
    searching by row and column index
    '''
    alpha = string.ascii_uppercase
    rotater = collections.deque(alpha)
    vigsquare_list = []
    for i in xrange(26):
        vigsquare_list.append(''.join(rotater))
        rotater.rotate(-1)
    if printable:
        return '\n'.join(vigsquare_list) 
    else:
        return ''.join(vigsquare_list)

和

def vigenere(row, column):
    ''' 
    Return a character from a vigenere square by 
    row and column letter.
    vigenere('L', 'G') returns 'R'
    '''
    alpha = string.ascii_uppercase
    rowindex = alpha.find(row)
    columnindex = alpha.find(column)
    return vigsquare()[rowindex*26 + columnindex]

print vigsquare(printable=True)
vigenere('L', 'G')

给你：

ABCDEFGHIJKLMNOPQRSTUVWXYZ
BCDEFGHIJKLMNOPQRSTUVWXYZA
CDEFGHIJKLMNOPQRSTUVWXYZAB
DEFGHIJKLMNOPQRSTUVWXYZABC
EFGHIJKLMNOPQRSTUVWXYZABCD
FGHIJKLMNOPQRSTUVWXYZABCDE
GHIJKLMNOPQRSTUVWXYZABCDEF
HIJKLMNOPQRSTUVWXYZABCDEFG
IJKLMNOPQRSTUVWXYZABCDEFGH
JKLMNOPQRSTUVWXYZABCDEFGHI
KLMNOPQRSTUVWXYZABCDEFGHIJ
LMNOPQRSTUVWXYZABCDEFGHIJK
MNOPQRSTUVWXYZABCDEFGHIJKL
NOPQRSTUVWXYZABCDEFGHIJKLM
OPQRSTUVWXYZABCDEFGHIJKLMN
PQRSTUVWXYZABCDEFGHIJKLMNO
QRSTUVWXYZABCDEFGHIJKLMNOP
RSTUVWXYZABCDEFGHIJKLMNOPQ
STUVWXYZABCDEFGHIJKLMNOPQR
TUVWXYZABCDEFGHIJKLMNOPQRS
UVWXYZABCDEFGHIJKLMNOPQRST
VWXYZABCDEFGHIJKLMNOPQRSTU
WXYZABCDEFGHIJKLMNOPQRSTUV
XYZABCDEFGHIJKLMNOPQRSTUVW
YZABCDEFGHIJKLMNOPQRSTUVWX
ZABCDEFGHIJKLMNOPQRSTUVWXY

和

'R'

这里有另一个看起来很有趣的解决方案，但我不相信它，因为我不理解它，所以我将对我的代码和其他代码进行单元测试，看看它是否可靠。

def vig_2(row, col):
    return string.ascii_uppercase[(ord(row) + ord(col)) % 26]

并通过单元测试比较了这两种方法。如果它是正确的，第二个（从 NPE 借来的，我现在欠他一个赞成票）可能会更好：

import unittest
class VigTestCase(unittest.TestCase):
    def test_vigenere(self):
        self.assertEqual(vigenere('L', 'G'), 'R')
    def test_vigsquare(self):
        self.assertEqual(vigsquare(printable=False), 'ABCDEFGHIJKLMNOPQRSTUVWXYZBCDEFGHIJKLMNOPQRSTUVWXYZACDEFGHIJKLMNOPQRSTUVWXYZABDEFGHIJKLMNOPQRSTUVWXYZABCEFGHIJKLMNOPQRSTUVWXYZABCDFGHIJKLMNOPQRSTUVWXYZABCDEGHIJKLMNOPQRSTUVWXYZABCDEFHIJKLMNOPQRSTUVWXYZABCDEFGIJKLMNOPQRSTUVWXYZABCDEFGHJKLMNOPQRSTUVWXYZABCDEFGHIKLMNOPQRSTUVWXYZABCDEFGHIJLMNOPQRSTUVWXYZABCDEFGHIJKMNOPQRSTUVWXYZABCDEFGHIJKLNOPQRSTUVWXYZABCDEFGHIJKLMOPQRSTUVWXYZABCDEFGHIJKLMNPQRSTUVWXYZABCDEFGHIJKLMNOQRSTUVWXYZABCDEFGHIJKLMNOPRSTUVWXYZABCDEFGHIJKLMNOPQSTUVWXYZABCDEFGHIJKLMNOPQRTUVWXYZABCDEFGHIJKLMNOPQRSUVWXYZABCDEFGHIJKLMNOPQRSTVWXYZABCDEFGHIJKLMNOPQRSTUWXYZABCDEFGHIJKLMNOPQRSTUVXYZABCDEFGHIJKLMNOPQRSTUVWYZABCDEFGHIJKLMNOPQRSTUVWXZABCDEFGHIJKLMNOPQRSTUVWXY')
    def test_vig2(self):
        for i in string.ascii_uppercase:
            for j in string.ascii_uppercase:
                self.assertEqual(vig_2(i, j), vigenere(i, j))

unittest.main()
...
----------------------------------------------------------------------
Ran 3 tests in 0.038s

OK

所以看起来 NPE 有一个很好的解决方案！