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Vigenere Cipher.py
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Vigenere Cipher.py
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from itertools import cycle
VALIDCHARS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
def GetKeyStream(decrypted, encrypted):
for i in range(26):
if ((VALIDCHARS.index(decrypted) + i) % 26
== VALIDCHARS.index(encrypted)):
return i
def RemoveDups(ListObject):
return map(list, set(map(tuple, ListObject)))
def GetKey(KeyStream):
for i in range(1, len(KeyStream) + 1):
SubKeys = [KeyStream[j:j + i] for j in range(0, len(KeyStream), i)]
if len(SubKeys) == 1:
return SubKeys[0]
elif (len(RemoveDups(SubKeys[:-1])) == 1
and SubKeys[-1] == SubKeys[0][:len(SubKeys[-1])]):
return SubKeys[0]
def OriginalChar(encrypted, key):
for i in range(26):
if (i + key) % 26 == VALIDCHARS.index(encrypted):
return VALIDCHARS[i]
def decode_vigenere(old_decrypted, old_encrypted, new_encrypted):
EncryptKeyStream = [GetKeyStream(old_decrypted[i], old_encrypted[i])
for i in range(len(old_decrypted))]
EncryptKey = GetKey(EncryptKeyStream)
NewEncryptKey = []
counter = len(new_encrypted)
for i in cycle(EncryptKey):
NewEncryptKey.append(i)
counter -= 1
if not counter:
break
# print NewEncryptKey
return ''.join([OriginalChar(new_encrypted[i], NewEncryptKey[i])
for i in range(len(new_encrypted))])
# These "asserts" using only for self-checking and not necessary for
# auto-testing
if __name__ == '__main__':
assert decode_vigenere(u'DONTWORRYBEHAPPY',
u'FVRVGWFTFFGRIDRF',
u'DLLCZXMFVRVGWFTF') == "BEHAPPYDONTWORRY", "CHECKIO"
assert decode_vigenere(u'HELLO', u'OIWWC', u'ICP') == "BYE", "HELLO"
assert decode_vigenere(u'LOREMIPSUM',
u'OCCSDQJEXA',
u'OCCSDQJEXA') == "LOREMIPSUM", "DOLORIUM"