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Task/ADFGVX-cipher/Python/adfgvx-cipher.py

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+"""
+    The ADFGVX cipher implemented as a Python class
+    See also eg. https://www.nku.edu/~christensen/092hnr304%20ADFGVX.pdf
+"""
+
+from random import shuffle, choice
+from itertools import product, accumulate
+from numpy import floor, sqrt
+
+class ADFGVX:
+    """ The WWI German ADFGVX cipher. """
+    def __init__(self, spoly, k, alph='ADFGVX'):
+        self.polybius = list(spoly.upper())
+        self.pdim = int(floor(sqrt(len(self.polybius))))
+        self.key = list(k.upper())
+        self.keylen = len(self.key)
+        self.alphabet = list(alph)
+        pairs = [p[0] + p[1] for p in product(self.alphabet, self.alphabet)]
+        self.encode = dict(zip(self.polybius, pairs))
+        self.decode = dict((v, k) for (k, v) in self.encode.items())
+
+    def encrypt(self, msg):
+        """ Encrypt with the ADFGVX cipher. """
+        chars = list(''.join([self.encode[c] for c in msg.upper() if c in self.polybius]))
+        colvecs = [(lett, chars[i:len(chars):self.keylen]) \
+            for (i, lett) in enumerate(self.key)]
+        colvecs.sort(key=lambda x: x[0])
+        return ''.join([''.join(a[1]) for a in colvecs])
+
+    def decrypt(self, cod):
+        """ Decrypt with the ADFGVX cipher. Does not depend on spacing of encoded text """
+        chars = [c for c in cod if c in self.alphabet]
+        sortedkey = sorted(self.key)
+        order = [self.key.index(ch) for ch in sortedkey]
+        originalorder = [sortedkey.index(ch) for ch in self.key]
+        base, extra = divmod(len(chars), self.keylen)
+        strides = [base + (1 if extra > i else 0) for i in order]    # shuffled column lengths
+        starts = list(accumulate(strides[:-1], lambda x, y: x + y))  # shuffled starts of columns
+        starts = [0] + starts                                        # starting index
+        ends = [starts[i] + strides[i] for i in range(self.keylen)]  # shuffled ends of columns
+        cols = [chars[starts[i]:ends[i]] for i in originalorder]     # get reordered columns
+        pairs = []                                                   # recover the rows
+        for i in range((len(chars) - 1) // self.keylen + 1):
+            for j in range(self.keylen):
+                if i * self.keylen + j < len(chars):
+                    pairs.append(cols[j][i])
+
+        return ''.join([self.decode[pairs[i] + pairs[i + 1]] for i in range(0, len(pairs), 2)])
+
+
+if __name__ == '__main__':
+    PCHARS = list('ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789')
+    shuffle(PCHARS)
+    POLYBIUS = ''.join(PCHARS)
+    with open('unixdict.txt') as fh:
+        WORDS = [w for w in (fh.read()).split() \
+            if len(w) == 9 and len(w) == len(set(list(w)))]
+        KEY = choice(WORDS)
+
+    SECRET, MESSAGE = ADFGVX(POLYBIUS, KEY), 'ATTACKAT1200AM'
+    print(f'Polybius: {POLYBIUS}, key: {KEY}')
+    print('Message: ', MESSAGE)
+    ENCODED = SECRET.encrypt(MESSAGE)
+    DECODED = SECRET.decrypt(ENCODED)
+    print('Encoded: ', ENCODED)
+    print('Decoded: ', DECODED)