path: root/lc4.py

#!/usr/bin/python2
# -*- coding: utf-8 -*-
# This software is hereby released into public domain. Use it wisely.
# 
# ElsieFour (LC4) and its enhancement LS47
# version 2.7: 2018-02-13
#
# - Python script for LS47 originally written by Mirek Kratochvil (2017)
#   See https://github.com/exaexa/ls47
# - Python 3 port by Bernhard Esslinger / AK (Feb 2018)
#   See www.mysterytwisterc3.org
# - New options by CrypTool project (www.cryptool.org) (Feb 2018) in order to
#   support both ciphers LC4 and LS47, both ways to deal with nonces, keyword
#   usage for both LC4 and LS47, reading from file and commandline, and
#   extended test outputs.
# 
# Sample calls:
# - Using cipher LC4, enforced with option -6:
# python lc4-ls47.py -6 -ws thisismysecretkey -es its_my_fathers_son_but_not_my_brother -v -nl 6
# python lc4-ls47.py -6 -ws thisismysecretkey -ds q6xojffkncfyz#f5czs49#3mbsco#2iscvbnm#bymaf -v -nl 6
# - Using cipher LS47, enforced with option -7:
# python lc4-ls47.py -7 -ws s3cret_p4ssw0rd/31337 -ds y'zbvvs+d2,ky4sy?w(_wkz*7'90v:./s)kcz?mj+gyu8-'h(y,i+v,z+1ws -v -nl 10
# python lc4-ls47.py -7 -ws s3cret_p4ssw0rd/31337 -ds y'zbvvs+d2,ky4sy?w(_wkz*7'90v:./s)kcz?mj+gyu8-'h(y,i+v,z+1ws -v -ns 8y(l._4ct'
#


from __future__ import print_function
import sys
import os
import random
import argparse


version = "v2.7 (2018-02-13)"

letters6 = "#_23456789abcdefghijklmnopqrstuvwxyz"
letters7 = "_abcdefghijklmnopqrstuvwxyz.0123456789,-+*/:?!'()"


def missing_letters(s,t):
    return ''.join(sorted(set(c for c in s if c not in t)))


def check_key(key):
    illegal = missing_letters(key,letters)
    missing = missing_letters(letters,key)
    duplicates = ''.join(sorted(c for c in letters if key.count(c)>1))

    errors = []
    if illegal: errors.append( "Key contains illegal letters: '%s'" % illegal )
    if missing: errors.append( "Key misses some letters: '%s'" % missing )
    if duplicates: errors.append( "Key contains duplicate letters: '%s'" % duplicates )

    if errors:
        errors.append( "The key must be a permutation of the alphabet: %s" % letters )
        raise ValueError("\n".join(errors))


def check_nonce(nonce):
    illegal = missing_letters(nonce,letters)
    if illegal:
        raise ValueError("Nonce contains illegal letters: '%s'" % illegal)


def check_plaintext(s):
    illegal = missing_letters(s,letters)
    if illegal:
        raise ValueError("Plaintext contains illegal letters: '%s'" % illegal)


def check_ciphertext(s):
    illegal = missing_letters(s,letters)
    if illegal:
        raise ValueError("Ciphertext contains illegal letters: '%s'" % illegal)


def find_ix(letter):
    m = [l[1] for l in tiles if l[0] == letter]
    if len(m) != 1:
        raise ValueError("Letter '%c' not in the alphabet!" % letter)
    return m[0]


def find_pos(key, letter):
    p = key.find(letter)
    if not (0 <= p < size * size):
        raise ValueError("Letter '%c' not in key?!" % letter)
    return (p // size, p % size)


def add_pos(a, b):
    return ((a[0] + b[0]) % size, (a[1] + b[1]) % size)


def sub_pos(a, b):
    return ((a[0] - b[0]) % size, (a[1] - b[1]) % size)


def find_at_pos(key, coord):
    return key[coord[1] + coord[0] * size]


def rotate_right(key, row, n):
    mid = key[size * row:size * (row + 1)]
    return key[:size * row] + mid[-n:] + mid[:-n] + key[size * (row + 1):]


def rotate_down(key, col, n):
    lines  = [key[i * size:(i + 1) * size] for i in range(size)]
    lefts  = [l[:col] for l in lines]
    mids   = [l[col] for l in lines]
    rights = [l[col + 1:] for l in lines]
    mids = mids[-n:] + mids[:-n]
    return ''.join(lefts[i] + mids[i] + rights[i] for i in range(size))


def rotate_marker_right(m, row, n):
    if m[0] != row:
        return (m[0], m[1])
    else:
        return (m[0], (m[1] + n) % size)


def rotate_marker_down(m, col, n):
    if m[1] != col:
        return (m[0], m[1])
    else:
        return ((m[0] + n) % size, m[1])


def derive_key(password):
    i = 0
    k = letters
    for c in password:
        (row, col) = find_ix(c)
        k = rotate_down(rotate_right(k, i, col), i, row)
        i = (i + 1) % size
    return k


def encrypt(plaintext):
    global key, mp

    ciphertext = ''
    for p in plaintext:
        pp = find_pos(key, p)
        mix = find_ix(find_at_pos(key, mp))
        cp = add_pos(pp, mix)
        c = find_at_pos(key, cp)
        ciphertext += c

        key = rotate_right(key, pp[0], 1)
        if marker_mode==1: mp = rotate_marker_right(mp, pp[0], 1)
        cp = find_pos(key, c)
        key = rotate_down(key, cp[1], 1)
        if marker_mode==1: mp = rotate_marker_down(mp, cp[1], 1)
        mp = add_pos(mp, find_ix(c))
    return ciphertext


def decrypt(ciphertext):
    global key, mp
 
    plaintext = ''
    for c in ciphertext:
        cp = find_pos(key, c)
        mix = find_ix(find_at_pos(key, mp))
        pp = sub_pos(cp, mix)
        p = find_at_pos(key, pp)
        plaintext += p

        key = rotate_right(key, pp[0], 1)
        if marker_mode==1: mp = rotate_marker_right(mp, pp[0], 1)
        cp = find_pos(key, c)
        key = rotate_down(key, cp[1], 1)
        if marker_mode==1: mp = rotate_marker_down(mp, cp[1], 1)
        mp = add_pos(mp, find_ix(c))
    return plaintext


def create_random_nonce(size):
    return ''.join(random.choice(letters) for i in range(size))


def encrypt_with_nonce(plaintext):
    global nonce, nonce_enc

    ciphertext = encrypt(nonce + plaintext)
    nonce_enc = ciphertext[:nonce_size]

    if nonce_mode==1:
        return nonce + ciphertext[nonce_size:]
    else:
        return ciphertext


def decrypt_with_nonce(ciphertext):
    global nonce, nonce_enc

    if nonce_mode==1:
        nonce = ciphertext[:nonce_size]
        nonce_enc = encrypt(nonce)
        return decrypt(ciphertext[nonce_size:])
    else:
        plaintext = decrypt(ciphertext)
        nonce = plaintext[:nonce_size]
        nonce_enc = ciphertext[:nonce_size]
        return plaintext[nonce_size:]


def eprint(*args, **kwargs):
    print(*args, file=sys.stderr, **kwargs)


def printinfo(enc=False):
    eprint('CIPHER    : ' + ("LC4" if size==6 else "LS47"))
    eprint('ALPHABET  : ' + letters)
    if args.keywordstring:
        eprint('KEYWORD   : ' + args.keywordstring)
    eprint('KEY       : ' + initialkey)  # key variable modified during process?
    eprint('NONCE     : ' + nonce)
    eprint('NONCE ENC : ' + nonce_enc)
    eprint('NONCEMODE : ' + ("Kaminsky" if nonce_mode==1 else "Kratochvil"))
    eprint('MARKER    : ' + ("Kaminsky" if marker_mode==1 else "Kratochvil"))
    if enc:
        eprint('PLAINTEXT : ' + plaintext)
        eprint('CIPHERTEXT: ' + ciphertext)
    else:
        eprint('CIPHERTEXT: ' + ciphertext)
        eprint('PLAINTEXT : ' + plaintext)


def test1(size):
    global letters, nonce_mode, marker_mode, tiles, noncelen, nonce, nonce_size, nonce_enc, signature
    global ciphertext, plaintext, key, initialkey, mp

    if size == 7:
        CIPHERNAME = "LS47"
        letters = letters7;
        nonce_mode = 2
        marker_mode = 2
        noncelen=10; nonce = create_random_nonce(noncelen)
        # nonce = 'dr0+:_pij2'  # just a sample for testing fixed nonce
    else:
        CIPHERNAME = "LC4"
        letters = letters6;
        nonce_mode = 1
        marker_mode = 1
        noncelen=6; nonce = create_random_nonce(noncelen)
        # nonce = 'pjpm5i'  # just a sample for testing fixed nonce

    tiles = list(zip(letters, [(x // size, x % size) for x in range(size * size)]))
    check_nonce(nonce)
    nonce_size = len(nonce)
    nonce_enc = ""

    print('\n' + CIPHERNAME)

    if size == 7:
        keyword = 's3cret_p4ssw0rd/31337'; args.keywordstring=keyword
        key = derive_key(keyword)
    else:
        key = letters
    initialkey = key
    check_key(key)
    mp = (0, 0)

    if size == 7:
        plaintext = 'conflagrate_the_rose_bush_at_six!'
        signature = 'peace-vector-3'
    else:
        plaintext = 'its_my_fathers_son_but_not_my_brother'
        signature = '#its_me'   # signature = ''

    check_plaintext(plaintext)
    ciphertext = encrypt_with_nonce(plaintext)

    key = initialkey; mp = (0, 0)  # initialization again
    check_ciphertext(ciphertext)
    decryptedtext = decrypt_with_nonce(ciphertext)
    print('decrypted text: ' + decryptedtext)

    printinfo(True)
    args.keywordstring=''



if __name__ == '__main__':

    parser = argparse.ArgumentParser()

    mgroup = parser.add_mutually_exclusive_group()
    parser.add_argument("-v", "--verbose", help="output additional information on stderr", action="count", default=0)

    mgroup.add_argument("-6", "--lc4", help="use ElsieFour cipher (6x6 table) (default)", action="store_true")
    mgroup.add_argument("-7", "--ls47", help="use LS47 cipher (7x7 table)", action="store_true")

    mgroup2 = parser.add_mutually_exclusive_group()
    mgroup2.add_argument("-ks", "--keystring", metavar="STRING", help="use STRING as key")
    mgroup2.add_argument("-kf", "--keyfile", metavar="FILE", help="read key from FILE")
    mgroup2.add_argument("-ws", "--keywordstring", metavar="STRING", help="generate key from keyword STRING", default=None)
    mgroup2.add_argument("-wf", "--keywordfile", metavar="FILE", help="read keyword from FILE to generate key", default=None)

    mgroup3 = parser.add_mutually_exclusive_group()
    mgroup3.add_argument("-nl", "--noncelen", metavar="LENGTH", help="use random nonce of length LENGTH", type=int, default=0)
    mgroup3.add_argument("-ns", "--noncestring", metavar="STRING", help="use STRING as nonce")

    mgroup4 = parser.add_mutually_exclusive_group()
    mgroup4.add_argument("-es", "--encryptstring", metavar="STRING", help="encrypt STRING")
    mgroup4.add_argument("-ef", "--encryptfile", metavar="FILE", help="read plaintext from FILE and encrypt it")
    mgroup4.add_argument("-ds", "--decryptstring", metavar="STRING", help="decrypt STRING")
    mgroup4.add_argument("-df", "--decryptfile", metavar="FILE", help="read ciphertext from FILE and decrypt it")
    mgroup4.add_argument("-t", "--test", help="encrypt and decrypt a string with a random nonce and a given key (once with LC4 and once with LS47)", action="store_true")

    mgroup5 = parser.add_mutually_exclusive_group()
    mgroup5.add_argument("-n0", "--nKaminsky", help="use nonce in Kaminsky mode (default for LC4)", action="store_true")
    mgroup5.add_argument("-n1", "--nKratochvil", help="use nonce in Kratochvil mode (default for LS47)", action="store_true")

    mgroup6 = parser.add_mutually_exclusive_group()
    mgroup6.add_argument("-m0", "--mKaminsky", help="use marker in Kaminsky mode (default for LC4)", action="store_true")
    mgroup6.add_argument("-m1", "--mKratochvil", help="use marker in Kratochvil mode (default for LS47)", action="store_true")

    parser.add_argument("-s", "--signature", help="append SIGNATURE to plaintext when encrypting")

    args = parser.parse_args()

    if len(sys.argv)==1:
        parser.print_help()
        sys.exit(1)
    if args.verbose and len(sys.argv)==2:
        print('Version: ' + version)
        # parser.print_help()
        sys.exit(1)

    # set cipher

    if args.ls47:
        size = 7
        letters = letters7
    else:
        size = 6
        letters = letters6

    tiles = list(zip(letters, [(x // size, x % size) for x in range(size * size)]))

    # set nonce

    if args.noncestring:
        nonce = args.noncestring
    elif args.noncelen:
        nonce = create_random_nonce(args.noncelen)
    else:
        nonce = ""

    check_nonce(nonce)
    nonce_size = len(nonce)
    nonce_enc = ""

    # set nonce mode

    nonce_mode = 1 if size==6 else 2
    if args.nKaminsky: nonce_mode = 1
    if args.nKratochvil: nonce_mode = 2

    # set marker mode

    marker_mode = 1 if size==6 else 2
    if args.nKaminsky: marker_mode = 1
    if args.nKratochvil: marker_mode = 2

    # set key

    key = letters

    if args.keywordfile: args.keywordstring = open(args.keywordfile, 'r').read().rstrip('\r\n')
    if args.keywordstring: key = derive_key(args.keywordstring);

    if args.keyfile: args.keystring = open(args.keyfile, 'r').read().rstrip('\r\n')
    if args.keystring: key = args.keystring;

    initialkey = key
    check_key(key)

    mp = (0, 0)

    # encrypt / decrypt / test

    if args.encryptfile:
        args.encryptstring = open(args.encryptfile, 'r').read().rstrip('\r\n')

    if args.decryptfile:
        args.decryptstring = open(args.decryptfile, 'r').read().rstrip('\r\n')

    if args.encryptstring:
        plaintext = args.encryptstring
        if args.signature: plaintext += args.signature
        check_plaintext(plaintext)
        ciphertext = encrypt_with_nonce(plaintext)
        if args.verbose: printinfo(True)
        print(ciphertext)

    elif args.decryptstring:
        ciphertext = args.decryptstring
        check_ciphertext(ciphertext)
        plaintext = decrypt_with_nonce(ciphertext)
        if args.verbose: printinfo()
        if args.signature and args.verbose:
            eprint("Warning: the given signature is ignored during decryption")
        print(plaintext)

    elif args.test:
        print('\nVersion: ' + version)
        print('Test: No nonce provided (only its length), so each call will produce a different ciphertext.')
        size = 7; test1(size)
        size = 6; test1(size)
        sys.exit(1)

    else:
        # if args.verbose: print('Version   : ' + version)
        print('ALPHABET  : ' + letters)
        print('KEY       : ' + initialkey)
        print('NONCE     : ' + nonce)