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1# Ryan Finley
2# 3/8/2018
3# AesEncryption.py
4
5import os
6import binascii
7import hashlib
8from Crypto import Random
9from Crypto.Cipher import AES
10
11# Sets the constant for block's size to 16
12BLOCK_SIZE = 16
13
14# Sets the current directory to 'src' so it can run on all systems
15os.chdir(os.path.dirname(os.path.realpath(__file__)))
16
17# This is used when encoding plaintext when about to encrypt with AES
18def pad(size):
19    return size + (BLOCK_SIZE - len(size) % BLOCK_SIZE) * chr(BLOCK_SIZE - len(size) % BLOCK_SIZE)
20
21# Used to decode the ciphertext after it has been decoded with the secret key
22def reverse_pad(size):
23    return size[:-ord(size[len(size) - 1:])]
24
25# This is used to get text when it is called from any of the Get Functions below
26def get_text_from_file(filename):
27    my_file = open(filename)
28    file_text = my_file.read().replace('\n', '')
29    my_file.close()
30    return file_text
31
32# ----------------------------------------------------------------------------
33# All "Get" functions obtain the file's text drom the data folder when called
34def get_secret_key():
35    return get_text_from_file('../data/key.txt')
36
37def get_plaintext():
38    return get_text_from_file('../data/plaintext.txt')
39
40def get_ciphertext():
41    return get_text_from_file('../data/ciphertext.txt')
42
43def get_randomized_iv():
44    hex_str = get_text_from_file('../data/iv.txt')
45    return binascii.unhexlify(hex_str)
46# ----------------------------------------------------------------------------
47
48# Creates and returns a randomized IV
49def create_randomized_iv():
50    iv = Random.new().read(BLOCK_SIZE)
51    my_file = open('../data/iv.txt', 'w')
52    my_file.write(iv.hex())
53    my_file.close()
54    return iv
55
56# Creates and returns a randomized secret key
57def generate_key():
58    secret_key = hashlib.sha256(os.urandom(16)).digest()
59    my_file = open('../data/key.txt', 'w')
60    my_file.write(secret_key.hex())
61    my_file.close()
62    return secret_key
63
64# --- Encryption Function ---
65# Inputs: secret key, plaintext message
66# Outputs: ciphertext from provided secret key and message
67def encryption(key, plaintext, mode):
68    iv = create_randomized_iv()
69    ciphertext = AES.new(key, mode, iv).encrypt(pad(plaintext)).hex()
70    my_file = open('../data/ciphertext.txt', 'w')
71    my_file.write(ciphertext)
72    my_file.close()
73    return ciphertext
74
75# Encrypts plaintext using ECB with no writing to any files
76def enc_for_ecb(key, plaintext):
77    return encryption(key, plaintext, AES.MODE_ECB)
78
79# Encrypts plaintext using CBC with no writing to any files
80def enc_for_cbc(key, plaintext):
81    return encryption(key, plaintext, AES.MODE_CBC)
82
83# --- Decryption Function ---
84# Inputs: secret key, ciphertext, IV, and a mode type (CBC or ECB)
85# Outputs: decrypted ciphertext and stores value in appropriate file
86def decryption(key, ciphertext, iv, mode):
87    temp_cipher = AES.new(key, mode, iv)
88    plaintext_dec = reverse_pad(temp_cipher.decrypt(binascii.unhexlify(ciphertext))).decode('utf-8')
89    my_file = open('../data/result.txt', 'w')
90    my_file.write(plaintext_dec)
91    my_file.close()
92    return plaintext_dec
93
94def compare_aes_enc_modes():
95    for i in range(0, 3):
96        secret_key = generate_key()
97        plaintext = get_plaintext()
98        ecb_enc = enc_for_ecb(secret_key, plaintext)
99        cdc_enc = enc_for_ecb(secret_key, plaintext)
100        print('Encrptyion Rounnd ' + str(i+1))
101        print('Enc with ECB: ' + ecb_enc)
102        print('Enc with CBC: ' + cbc_enc)
103        print('\n')
104
105sk = generate_key()
106
107# ---------------------- Displayed output begins here ----------------------
108# EBC
109print('\n')
110ecb_enc = encryption(sk, get_plaintext(), AES.MODE_ECB)
111ecb_dec = decryption(sk, ecb_enc, get_randomized_iv(), AES.MODE_ECB)
112print('Encrypted with ECB: ' + ecb_enc)
113print('Decrypted with ECB: ' + ecb_dec)
114
115# CBC
116print('\n')
117cbc_enc = encryption(sk, get_plaintext(), AES.MODE_CBC)
118cbc_dec = decryption(sk, cbc_enc, get_randomized_iv(), AES.MODE_CBC)
119print('Enc with CBC: ' + cbc_enc)
120print('Decrypt with CBC: ' + cbc_dec)
121
122print('\n')
123compare_aes_enc_modes()
124print('\n')