XOR cipher algorithm

a class with simple cipher algorithm that uses bitwise XOR

ciphers/XOR_cipher.py

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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))
+
+		# testing for default arguments
+		if (key == 0):
+			if (self.__key == 0):
+				key = 1
+			else:
+				key = self.__key
+
+		# make sure key can be any size
+		while (key > 255):
+			key -= 255
+
+		# This will be returned
+		ans = []
+		resultNumber = 0
+
+		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))
+
+		# testing for default arguments
+		if (key == 0):
+			if (self.__key == 0):
+				key = 1
+			else:
+				key = self.__key
+
+		# make sure key can be any size
+		while (key > 255):
+			key -= 255
+
+		# This will be returned
+		ans = []
+		resultNumber = 0
+
+		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))
+
+		# testing for default arguments
+		if (key == 0):
+			if (self.__key == 0):
+				key = 1
+			else:
+				key = self.__key
+
+		# make sure key can be any size
+		while (key > 255):
+			key -= 255
+
+		# This will be returned
+		ans = ""
+		resultNumber = 0
+
+		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))
+
+		# testing for default arguments
+		if (key == 0):
+			if (self.__key == 0):
+				key = 1
+			else:
+				key = self.__key
+
+		# make sure key can be any size
+		while (key > 255):
+			key -= 255
+
+		# This will be returned
+		ans = ""
+		resultNumber = 0
+
+		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:
+			fin = open(file,"r")
+			fout = open("encrypt.out","w+")
+
+			# actual encrypt-process
+			for line in fin:
+				fout.write(self.encrypt_string(line,key))
+
+			fin.close()
+			fout.close()
+
+		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:
+			fin = open(file,"r")
+			fout = open("decrypt.out","w+")
+
+			# actual encrypt-process
+			for line in fin:
+				fout.write(self.decrypt_string(line,key))
+
+			fin.close()
+			fout.close()
+
+		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("a.out",key)):
+# 	print "decrypt successful"
+# else:
+# 	print "decrypt unsuccessful"