vigenere cipher

vigenere-cipher.py

# encoding: utf8
# vigenere cipher
# https://stackoverflow.com/a/2490718/1675586

def encode(key, string):
    encoded_chars = []
    for i in range(len(string)):
        key_c = key[i % len(key)]
        encoded_c = chr(ord(string[i]) + ord(key_c) % 256)
        encoded_chars.append(encoded_c)
    encoded_string = ''.join(encoded_chars)
    return encoded_string

def decode(key, string):
    encoded_chars = []
    for i in range(len(string)):
        key_c = key[i % len(key)]
        encoded_c = chr((ord(string[i]) - ord(key_c) + 256) % 256)
        encoded_chars.append(encoded_c)
    encoded_string = ''.join(encoded_chars)
    return encoded_string

e = encode('a key', 'a message')
d = decode('a key', e)
print([e])
print([d])

# python 3
# ['Â@ØÊìÔ\x81ÒÊ']
# ['a message']

# python 2
# ['\xc2@\xd8\xca\xec\xd4\x81\xd2\xca']
# ['a message']


#--------------------------------------------------
# this version makes it also base64:


import six, base64

def encode(key, string):
    encoded_chars = []
    for i in range(len(string)):
        key_c = key[i % len(key)]
        encoded_c = chr(ord(string[i]) + ord(key_c) % 256)
        encoded_chars.append(encoded_c)
    encoded_string = ''.join(encoded_chars)
    encoded_string = encoded_string.encode('latin') if six.PY3 else encoded_string
    return base64.urlsafe_b64encode(encoded_string).rstrip(b'=')

def decode(key, string):
    string = base64.urlsafe_b64decode(string + b'===')
    string = string.decode('latin') if six.PY3 else string
    encoded_chars = []
    for i in range(len(string)):
        key_c = key[i % len(key)]
        encoded_c = chr((ord(string[i]) - ord(key_c) + 256) % 256)
        encoded_chars.append(encoded_c)
    encoded_string = ''.join(encoded_chars)
    return encoded_string

e = encode('a key', 'a message')
d = decode('a key', e)
print([e])
print([d])

# python 3
# [b'wkDYyuzUgdLK']
# ['a message']

# python 2
# ['wkDYyuzUgdLK']
# ['a message']

def forcode(key, string, act='d'):
    encoded_chars = []
    for i in range(len(string)):
        key_c = key[i % len(key)]
        if act!='d':
            encoded_c = chr(ord(string[i]) + ord(key_c) % 256)
        else:
            encoded_c = chr((ord(string[i]) - ord(key_c) + 256) % 256)
        encoded_chars.append(encoded_c)
    encoded_string = ''.join(encoded_chars)
    return encoded_string

e = forcode('a key', 'a message')
d = forcode('a key', e, '')

Thank you, Iman and Alex! This is exactly what I needed.

Thanks alex!!! This helped greatly!!!

thanks!

Hey @alex-pancho , can you please explain what you did?

@ademidun

Hey @alex-pancho , can you please explain what you did?

I wrote this answer a long time ago. There seems to be a question whether it is possible to cut everything into one function. Indeed, if you look closely at the code, you will notice that the difference is only one line.
But now, I would have done the code a little differently:

def forcode(key, string, act='e'):
    '''vigenere cipher function, use (key,text) for encoding and (key,text, 'd') for decoding'''
    
    encoded_chars = []
    for i in range(len(string)):
        key_c = key[i % len(key)]
        if act=='e':
            encoded_c = chr(ord(string[i]) + ord(key_c) % 256)
        else:
            encoded_c = chr((ord(string[i]) - ord(key_c) + 256) % 256)
        encoded_chars.append(encoded_c)
    encoded_string = ''.join(encoded_chars)
    return encoded_string

useex:
e = forcode('a key', 'a message')
d = forcode('a key', e,'d')
print(e)
print(d)

nice

For base64 version

import six
import base64


def enc_or_dec(key: str, string: str, dec: bool = False) -> str:
    encoded_chars = []
    if dec:
        string = base64.urlsafe_b64decode(string + b'===')
        string = string.decode('latin') if six.PY3 else string

    for i in range(len(string)):
        key_c = key[i % len(key)]
        if dec:
            encoded_c = chr((ord(string[i]) - ord(key_c) + 256) % 256)

        encoded_c = chr(ord(string[i]) + ord(key_c) % 256)
        encoded_chars.append(encoded_c)

    encoded_string = ''.join(encoded_chars)
    if dec:
        return encoded_string
    encoded_string = encoded_string.encode('latin') if six.PY3 else encoded_string
    return base64.urlsafe_b64encode(encoded_string).rstrip(b'=')

Usage:

key = 'zm'
msg  = 'test'

encoded = enc_or_dec(key, msg)
print(encoded)
decoded = enc_or_dec(key, encoded, True)
print(decoded)