Python/ciphers/xor_cipher.py

"""
	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")