class Bifid(Cipher):
"""The Bifid Cipher is a fractionating cipher, and has a key consisting of a 25 letter keysquare (with a letter removed e.g. 'J'), along with
a 'period', which is an integer.
For more information, the algorithm can be
seen e.g. http://www.practicalcryptography.com/ciphers/bifid-cipher/
:param key: The keysquare, as a 25 character string.
:param period: an integer.
"""
def __init__(self,key='phqgmeaylnofdxkrcvszwbuti',period=5):
self.key = [k.upper() for k in key]
self.pb = PolybiusSquare(self.key,size=5)
self.period = period
assert len(key)==25, 'invalid key in init: must have length 25, has length '+str(len(key))
assert period>=1, 'invalid period in init: period should be >= 1'
def encipher(self,string):
"""Encipher string using Bifid cipher according to initialised key. Punctuation and whitespace
are removed from the input.
Example::
ciphertext = Bifid('phqgmeaylnofdxkrcvszwbuti',5).encipher(plaintext)
:param string: The string to encipher.
:returns: The enciphered string.
"""
string = self.remove_punctuation(string)
step1 = self.pb.encipher(string)
evens = step1[::2]
odds = step1[1::2]
step2 = []
for i in range(0,len(string),self.period):
step2 += evens[i:i+self.period]
step2 += odds[i:i+self.period]
return self.pb.decipher(''.join(step2))
def decipher(self,string):
"""Decipher string using Bifid cipher according to initialised key. Punctuation and whitespace
are removed from the input.
Example::
plaintext = Bifid('phqgmeaylnofdxkrcvszwbuti',5).decipher(ciphertext)
:param string: The string to decipher.
:returns: The deciphered string.
"""
ret = ''
string = string.upper()
rowseq,colseq = [],[]
# take blocks of length period, reform rowseq,colseq from them
for i in range(0,len(string),self.period):
tempseq = []
for j in range(0,self.period):
if i+j >= len(string): continue
tempseq.append( self.key.index(string[i + j]) / 5 )
tempseq.append( self.key.index(string[i + j]) % 5 )
rowseq.extend(tempseq[0:len(tempseq)/2])
colseq.extend(tempseq[len(tempseq)/2:])
for i in range(len(rowseq)):
ret += self.key[rowseq[i]*5 + colseq[i]]
return ret
def crypto_polybius_decipher_api(key: 'The keysquare, each row one after the other. The key must by size^2 characters in length', size:type_key_square_size, chars:'the set of characters to use. By default ABCDE are used, this parameter should have the same length as size', msg: 'Message to be [de]ciphered'):
"""The Polybius square is a simple substitution cipher that outputs 2 characters of ciphertext for each character of plaintext. It has a key consisting
which depends on 'size'. By default 'size' is 5, and the key is 25 letters (5^2). For a size of 6 a 36 letter key required etc.
For a more detailed look at how it works see http://www.practicalcryptography.com/ciphers pycipher.polybius-square-cipher/"""
if len(key) == size**2 and len(chars) == size:
polybius = PolybiusSquare(key=key, size=size, chars=chars)
return polybius.decipher(msg)
else:
return 'Invalid parameters'