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"""

author: Christian Bender

date: 21.12.2017

class: XORCipher

This class implements the XOR-cipher algorithm and provides

some useful methods for encrypting and decrypting strings and

files.

Overview about methods

- encrypt : list of char

- decrypt : list of char

- encrypt_string : str

- decrypt_string : str

- encrypt_file : boolean

- decrypt_file : boolean

"""

class XORCipher(object):

def __init__(self, key = 0):

"""

simple constructor that receives a key or uses

default key = 0

"""

#private field

self.__key = key

def encrypt(self, content, key):

"""

input: 'content' of type string and 'key' of type int

output: encrypted string 'content' as a list of chars

if key not passed the method uses the key by the constructor.

otherwise key = 1

"""

# precondition

assert (isinstance(key,int) and isinstance(content,str))

key = key or self.__key or 1

# make sure key can be any size

while (key > 255):

key -= 255

# This will be returned

ans = []

for ch in content:

ans.append(chr(ord(ch) ^ key))

return ans

def decrypt(self,content,key):

"""

input: 'content' of type list and 'key' of type int

output: decrypted string 'content' as a list of chars

if key not passed the method uses the key by the constructor.

otherwise key = 1

"""

# precondition

assert (isinstance(key,int) and isinstance(content,list))

key = key or self.__key or 1

# make sure key can be any size

while (key > 255):

key -= 255

# This will be returned

ans = []

for ch in content:

ans.append(chr(ord(ch) ^ key))

return ans

def encrypt_string(self,content, key = 0):

"""

input: 'content' of type string and 'key' of type int

output: encrypted string 'content'

if key not passed the method uses the key by the constructor.

otherwise key = 1

"""

# precondition

assert (isinstance(key,int) and isinstance(content,str))

key = key or self.__key or 1

# make sure key can be any size

while (key > 255):

key -= 255

# This will be returned

ans = ""

for ch in content:

ans += chr(ord(ch) ^ key)

return ans

def decrypt_string(self,content,key = 0):

"""

input: 'content' of type string and 'key' of type int

output: decrypted string 'content'

if key not passed the method uses the key by the constructor.

otherwise key = 1

"""

# precondition

assert (isinstance(key,int) and isinstance(content,str))

key = key or self.__key or 1

# make sure key can be any size

while (key > 255):

key -= 255

# This will be returned

ans = ""

for ch in content:

ans += chr(ord(ch) ^ key)

return ans

def encrypt_file(self, file, key = 0):

"""

input: filename (str) and a key (int)

output: returns true if encrypt process was

successful otherwise false

if key not passed the method uses the key by the constructor.

otherwise key = 1

"""

#precondition

assert (isinstance(file,str) and isinstance(key,int))

try:

with open(file,"r") as fin:

with open("encrypt.out","w+") as fout:

# actual encrypt-process

for line in fin:

fout.write(self.encrypt_string(line,key))

except:

return False

return True

def decrypt_file(self,file, key):

"""

input: filename (str) and a key (int)

output: returns true if decrypt process was

successful otherwise false

if key not passed the method uses the key by the constructor.

otherwise key = 1

"""

#precondition

assert (isinstance(file,str) and isinstance(key,int))

try:

with open(file,"r") as fin:

with open("decrypt.out","w+") as fout:

# actual encrypt-process

for line in fin:

fout.write(self.decrypt_string(line,key))

except:

return False

return True

# Tests

# crypt = XORCipher()

# key = 67

# # test enrcypt

# print crypt.encrypt("hallo welt",key)

# # test decrypt

# print crypt.decrypt(crypt.encrypt("hallo welt",key), key)

# # test encrypt_string

# print crypt.encrypt_string("hallo welt",key)

# # test decrypt_string

# print crypt.decrypt_string(crypt.encrypt_string("hallo welt",key),key)

# if (crypt.encrypt_file("test.txt",key)):

# print "encrypt successful"

# else:

# print "encrypt unsuccessful"

# if (crypt.decrypt_file("encrypt.out",key)):

# print "decrypt successful"

# else:

# print "decrypt unsuccessful"