1+ """
2+ author: Christian Bender
3+ date: 21.12.2017
4+ class: XORCipher
5+
6+ This class implements the XOR-cipher algorithm and provides
7+ some useful methods for encrypting and decrypting strings and
8+ files.
9+
10+ Overview about methods
11+
12+ - encrypt : list of char
13+ - decrypt : list of char
14+ - encrypt_string : str
15+ - decrypt_string : str
16+ - encrypt_file : boolean
17+ - decrypt_file : boolean
18+ """
19+ class XORCipher (object ):
20+
21+ def __init__ (self , key = 0 ):
22+ """
23+ simple constructor that receives a key or uses
24+ default key = 0
25+ """
26+
27+ #private field
28+ self .__key = key
29+
30+ def encrypt (self , content , key ):
31+ """
32+ input: 'content' of type string and 'key' of type int
33+ output: encrypted string 'content' as a list of chars
34+ if key not passed the method uses the key by the constructor.
35+ otherwise key = 1
36+ """
37+
38+ # precondition
39+ assert (isinstance (key ,int ) and isinstance (content ,str ))
40+
41+ # testing for default arguments
42+ if (key == 0 ):
43+ if (self .__key == 0 ):
44+ key = 1
45+ else :
46+ key = self .__key
47+
48+ # make sure key can be any size
49+ while (key > 255 ):
50+ key -= 255
51+
52+ # This will be returned
53+ ans = []
54+ resultNumber = 0
55+
56+ for ch in content :
57+ ans .append (chr (ord (ch ) ^ key ))
58+
59+ return ans
60+
61+ def decrypt (self ,content ,key ):
62+ """
63+ input: 'content' of type list and 'key' of type int
64+ output: decrypted string 'content' as a list of chars
65+ if key not passed the method uses the key by the constructor.
66+ otherwise key = 1
67+ """
68+
69+ # precondition
70+ assert (isinstance (key ,int ) and isinstance (content ,list ))
71+
72+ # testing for default arguments
73+ if (key == 0 ):
74+ if (self .__key == 0 ):
75+ key = 1
76+ else :
77+ key = self .__key
78+
79+ # make sure key can be any size
80+ while (key > 255 ):
81+ key -= 255
82+
83+ # This will be returned
84+ ans = []
85+ resultNumber = 0
86+
87+ for ch in content :
88+ ans .append (chr (ord (ch ) ^ key ))
89+
90+ return ans
91+
92+
93+ def encrypt_string (self ,content , key = 0 ):
94+ """
95+ input: 'content' of type string and 'key' of type int
96+ output: encrypted string 'content'
97+ if key not passed the method uses the key by the constructor.
98+ otherwise key = 1
99+ """
100+
101+ # precondition
102+ assert (isinstance (key ,int ) and isinstance (content ,str ))
103+
104+ # testing for default arguments
105+ if (key == 0 ):
106+ if (self .__key == 0 ):
107+ key = 1
108+ else :
109+ key = self .__key
110+
111+ # make sure key can be any size
112+ while (key > 255 ):
113+ key -= 255
114+
115+ # This will be returned
116+ ans = ""
117+ resultNumber = 0
118+
119+ for ch in content :
120+ ans += chr (ord (ch ) ^ key )
121+
122+ return ans
123+
124+ def decrypt_string (self ,content ,key = 0 ):
125+ """
126+ input: 'content' of type string and 'key' of type int
127+ output: decrypted string 'content'
128+ if key not passed the method uses the key by the constructor.
129+ otherwise key = 1
130+ """
131+
132+ # precondition
133+ assert (isinstance (key ,int ) and isinstance (content ,str ))
134+
135+ # testing for default arguments
136+ if (key == 0 ):
137+ if (self .__key == 0 ):
138+ key = 1
139+ else :
140+ key = self .__key
141+
142+ # make sure key can be any size
143+ while (key > 255 ):
144+ key -= 255
145+
146+ # This will be returned
147+ ans = ""
148+ resultNumber = 0
149+
150+ for ch in content :
151+ ans += chr (ord (ch ) ^ key )
152+
153+ return ans
154+
155+
156+ def encrypt_file (self , file , key = 0 ):
157+ """
158+ input: filename (str) and a key (int)
159+ output: returns true if encrypt process was
160+ successful otherwise false
161+ if key not passed the method uses the key by the constructor.
162+ otherwise key = 1
163+ """
164+
165+ #precondition
166+ assert (isinstance (file ,str ) and isinstance (key ,int ))
167+
168+ try :
169+ fin = open (file ,"r" )
170+ fout = open ("encrypt.out" ,"w+" )
171+
172+ # actual encrypt-process
173+ for line in fin :
174+ fout .write (self .encrypt_string (line ,key ))
175+
176+ fin .close ()
177+ fout .close ()
178+
179+ except :
180+ return False
181+
182+ return True
183+
184+
185+ def decrypt_file (self ,file , key ):
186+ """
187+ input: filename (str) and a key (int)
188+ output: returns true if decrypt process was
189+ successful otherwise false
190+ if key not passed the method uses the key by the constructor.
191+ otherwise key = 1
192+ """
193+
194+ #precondition
195+ assert (isinstance (file ,str ) and isinstance (key ,int ))
196+
197+ try :
198+ fin = open (file ,"r" )
199+ fout = open ("decrypt.out" ,"w+" )
200+
201+ # actual encrypt-process
202+ for line in fin :
203+ fout .write (self .decrypt_string (line ,key ))
204+
205+ fin .close ()
206+ fout .close ()
207+
208+ except :
209+ return False
210+
211+ return True
212+
213+
214+
215+
216+ # Tests
217+ # crypt = XORCipher()
218+ # key = 67
219+
220+ # # test enrcypt
221+ # print crypt.encrypt("hallo welt",key)
222+ # # test decrypt
223+ # print crypt.decrypt(crypt.encrypt("hallo welt",key), key)
224+
225+ # # test encrypt_string
226+ # print crypt.encrypt_string("hallo welt",key)
227+
228+ # # test decrypt_string
229+ # print crypt.decrypt_string(crypt.encrypt_string("hallo welt",key),key)
230+
231+ # if (crypt.encrypt_file("test.txt",key)):
232+ # print "encrypt successful"
233+ # else:
234+ # print "encrypt unsuccessful"
235+
236+ # if (crypt.decrypt_file("a.out",key)):
237+ # print "decrypt successful"
238+ # else:
239+ # print "decrypt unsuccessful"
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