mixed_keyword_cypher.py

fromstringimportascii_uppercase


defmixed_keyword(
keyword: str, plaintext: str, verbose: bool=False, alphabet: str=ascii_uppercase
) ->str:
"""
 For keyword: hello

 H E L O
 A B C D
 F G I J
 K M N P
 Q R S T
 U V W X
 Y Z
 and map vertically

 >>> mixed_keyword("college", "UNIVERSITY", True) # doctest: +NORMALIZE_WHITESPACE
 {'A': 'C', 'B': 'A', 'C': 'I', 'D': 'P', 'E': 'U', 'F': 'Z', 'G': 'O', 'H': 'B',
 'I': 'J', 'J': 'Q', 'K': 'V', 'L': 'L', 'M': 'D', 'N': 'K', 'O': 'R', 'P': 'W',
 'Q': 'E', 'R': 'F', 'S': 'M', 'T': 'S', 'U': 'X', 'V': 'G', 'W': 'H', 'X': 'N',
 'Y': 'T', 'Z': 'Y'}
 'XKJGUFMJST'

 >>> mixed_keyword("college", "UNIVERSITY", False) # doctest: +NORMALIZE_WHITESPACE
 'XKJGUFMJST'
 """
keyword=keyword.upper()
plaintext=plaintext.upper()
alphabet_set=set(alphabet)

# create a list of unique characters in the keyword - their order matters
# it determines how we will map plaintext characters to the ciphertext
unique_chars= []
forcharinkeyword:
ifcharinalphabet_setandcharnotinunique_chars:
unique_chars.append(char)
# the number of those unique characters will determine the number of rows
num_unique_chars_in_keyword=len(unique_chars)

# create a shifted version of the alphabet
shifted_alphabet=unique_chars+ [
charforcharinalphabetifcharnotinunique_chars
 ]

# create a modified alphabet by splitting the shifted alphabet into rows
modified_alphabet= [
shifted_alphabet[k : k+num_unique_chars_in_keyword]
forkinrange(0, 26, num_unique_chars_in_keyword)
 ]

# map the alphabet characters to the modified alphabet characters
# going 'vertically' through the modified alphabet - consider columns first
mapping= {}
letter_index=0
forcolumninrange(num_unique_chars_in_keyword):
forrowinmodified_alphabet:
# if current row (the last one) is too short, break out of loop
iflen(row) <=column:
break

# map current letter to letter in modified alphabet
mapping[alphabet[letter_index]] =row[column]
letter_index+=1

ifverbose:
print(mapping)
# create the encrypted text by mapping the plaintext to the modified alphabet
return"".join(mapping.get(char, char) forcharinplaintext)


if__name__=="__main__":
# example use
print(mixed_keyword("college", "UNIVERSITY"))