Python/ciphers/playfair_cipher.py
ashu01 4fb978cf58 1. typo fix {playfair_cipher.py, AVL.py}
2. Corrected Logic {AVL.py, 104-107}
3. Removed unnecessary semicolons {BellmanFord.py, Dijkstra.py}
2017-12-31 14:30:31 +05:30

103 lines
2.8 KiB
Python

import string
import itertools
def chunker(seq, size):
it = iter(seq)
while True:
chunk = tuple(itertools.islice(it, size))
if not chunk:
return
yield chunk
def prepare_input(dirty):
"""
Prepare the plaintext by up-casing it
and separating repeated letters with X's
"""
dirty = ''.join([c.upper() for c in dirty if c in string.ascii_letters])
clean = ""
if len(dirty) < 2:
return dirty
for i in range(len(dirty)-1):
clean += dirty[i]
if dirty[i] == dirty[i+1]:
clean += 'X'
clean += dirty[-1]
if len(clean) & 1:
clean += 'X'
return clean
def generate_table(key):
# I and J are used interchangeably to allow
# us to use a 5x5 table (25 letters)
alphabet = "ABCDEFGHIKLMNOPQRSTUVWXYZ"
# we're using a list instead of a '2d' array because it makes the math
# for setting up the table and doing the actual encoding/decoding simpler
table = []
# copy key chars into the table if they are in `alphabet` ignoring duplicates
for char in key.upper():
if char not in table and char in alphabet:
table.append(char)
# fill the rest of the table in with the remaining alphabet chars
for char in alphabet:
if char not in table:
table.append(char)
return table
def encode(plaintext, key):
table = generate_table(key)
plaintext = prepare_input(plaintext)
ciphertext = ""
# https://en.wikipedia.org/wiki/Playfair_cipher#Description
for char1, char2 in chunker(plaintext, 2):
row1, col1 = divmod(table.index(char1), 5)
row2, col2 = divmod(table.index(char2), 5)
if row1 == row2:
ciphertext += table[row1*5+(col1+1)%5]
ciphertext += table[row2*5+(col2+1)%5]
elif col1 == col2:
ciphertext += table[((row1+1)%5)*5+col1]
ciphertext += table[((row2+1)%5)*5+col2]
else: # rectangle
ciphertext += table[row1*5+col2]
ciphertext += table[row2*5+col1]
return ciphertext
def decode(ciphertext, key):
table = generate_table(key)
plaintext = ""
# https://en.wikipedia.org/wiki/Playfair_cipher#Description
for char1, char2 in chunker(ciphertext, 2):
row1, col1 = divmod(table.index(char1), 5)
row2, col2 = divmod(table.index(char2), 5)
if row1 == row2:
plaintext += table[row1*5+(col1-1)%5]
plaintext += table[row2*5+(col2-1)%5]
elif col1 == col2:
plaintext += table[((row1-1)%5)*5+col1]
plaintext += table[((row2-1)%5)*5+col2]
else: # rectangle
plaintext += table[row1*5+col2]
plaintext += table[row2*5+col1]
return plaintext