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f3bcebb1 | 1 | __all__ = ['aes_encrypt', 'key_expansion', 'aes_ctr_decrypt', 'aes_decrypt_text'] |
2 | ||
3 | import base64 | |
4 | from math import ceil | |
5 | ||
48ea9cea PH |
6 | from .utils import bytes_to_intlist |
7 | ||
f3bcebb1 | 8 | BLOCK_SIZE_BYTES = 16 |
9 | ||
10 | def aes_ctr_decrypt(data, key, counter): | |
11 | """ | |
12 | Decrypt with aes in counter mode | |
13 | ||
14 | @param {int[]} data cipher | |
15 | @param {int[]} key 16/24/32-Byte cipher key | |
16 | @param {instance} counter Instance whose next_value function (@returns {int[]} 16-Byte block) | |
17 | returns the next counter block | |
18 | @returns {int[]} decrypted data | |
19 | """ | |
20 | expanded_key = key_expansion(key) | |
6e74bc41 | 21 | block_count = int(ceil(float(len(data)) / BLOCK_SIZE_BYTES)) |
f3bcebb1 | 22 | |
23 | decrypted_data=[] | |
24 | for i in range(block_count): | |
25 | counter_block = counter.next_value() | |
26 | block = data[i*BLOCK_SIZE_BYTES : (i+1)*BLOCK_SIZE_BYTES] | |
27 | block += [0]*(BLOCK_SIZE_BYTES - len(block)) | |
28 | ||
29 | cipher_counter_block = aes_encrypt(counter_block, expanded_key) | |
30 | decrypted_data += xor(block, cipher_counter_block) | |
31 | decrypted_data = decrypted_data[:len(data)] | |
32 | ||
33 | return decrypted_data | |
34 | ||
35 | def key_expansion(data): | |
36 | """ | |
37 | Generate key schedule | |
38 | ||
39 | @param {int[]} data 16/24/32-Byte cipher key | |
40 | @returns {int[]} 176/208/240-Byte expanded key | |
41 | """ | |
42 | data = data[:] # copy | |
43 | rcon_iteration = 1 | |
44 | key_size_bytes = len(data) | |
48ea9cea | 45 | expanded_key_size_bytes = (key_size_bytes // 4 + 7) * BLOCK_SIZE_BYTES |
f3bcebb1 | 46 | |
47 | while len(data) < expanded_key_size_bytes: | |
48 | temp = data[-4:] | |
49 | temp = key_schedule_core(temp, rcon_iteration) | |
50 | rcon_iteration += 1 | |
51 | data += xor(temp, data[-key_size_bytes : 4-key_size_bytes]) | |
52 | ||
53 | for _ in range(3): | |
54 | temp = data[-4:] | |
55 | data += xor(temp, data[-key_size_bytes : 4-key_size_bytes]) | |
56 | ||
57 | if key_size_bytes == 32: | |
58 | temp = data[-4:] | |
59 | temp = sub_bytes(temp) | |
60 | data += xor(temp, data[-key_size_bytes : 4-key_size_bytes]) | |
61 | ||
62 | for _ in range(3 if key_size_bytes == 32 else 2 if key_size_bytes == 24 else 0): | |
63 | temp = data[-4:] | |
64 | data += xor(temp, data[-key_size_bytes : 4-key_size_bytes]) | |
65 | data = data[:expanded_key_size_bytes] | |
66 | ||
67 | return data | |
68 | ||
69 | def aes_encrypt(data, expanded_key): | |
70 | """ | |
71 | Encrypt one block with aes | |
72 | ||
73 | @param {int[]} data 16-Byte state | |
74 | @param {int[]} expanded_key 176/208/240-Byte expanded key | |
75 | @returns {int[]} 16-Byte cipher | |
76 | """ | |
48ea9cea | 77 | rounds = len(expanded_key) // BLOCK_SIZE_BYTES - 1 |
f3bcebb1 | 78 | |
79 | data = xor(data, expanded_key[:BLOCK_SIZE_BYTES]) | |
80 | for i in range(1, rounds+1): | |
81 | data = sub_bytes(data) | |
82 | data = shift_rows(data) | |
83 | if i != rounds: | |
84 | data = mix_columns(data) | |
85 | data = xor(data, expanded_key[i*BLOCK_SIZE_BYTES : (i+1)*BLOCK_SIZE_BYTES]) | |
86 | ||
87 | return data | |
88 | ||
89 | def aes_decrypt_text(data, password, key_size_bytes): | |
90 | """ | |
91 | Decrypt text | |
92 | - The first 8 Bytes of decoded 'data' are the 8 high Bytes of the counter | |
93 | - The cipher key is retrieved by encrypting the first 16 Byte of 'password' | |
94 | with the first 'key_size_bytes' Bytes from 'password' (if necessary filled with 0's) | |
95 | - Mode of operation is 'counter' | |
96 | ||
97 | @param {str} data Base64 encoded string | |
98 | @param {str,unicode} password Password (will be encoded with utf-8) | |
99 | @param {int} key_size_bytes Possible values: 16 for 128-Bit, 24 for 192-Bit or 32 for 256-Bit | |
100 | @returns {str} Decrypted data | |
101 | """ | |
102 | NONCE_LENGTH_BYTES = 8 | |
103 | ||
48ea9cea PH |
104 | data = bytes_to_intlist(base64.b64decode(data)) |
105 | password = bytes_to_intlist(password.encode('utf-8')) | |
f3bcebb1 | 106 | |
107 | key = password[:key_size_bytes] + [0]*(key_size_bytes - len(password)) | |
48ea9cea | 108 | key = aes_encrypt(key[:BLOCK_SIZE_BYTES], key_expansion(key)) * (key_size_bytes // BLOCK_SIZE_BYTES) |
f3bcebb1 | 109 | |
110 | nonce = data[:NONCE_LENGTH_BYTES] | |
111 | cipher = data[NONCE_LENGTH_BYTES:] | |
112 | ||
113 | class Counter: | |
114 | __value = nonce + [0]*(BLOCK_SIZE_BYTES - NONCE_LENGTH_BYTES) | |
115 | def next_value(self): | |
116 | temp = self.__value | |
117 | self.__value = inc(self.__value) | |
118 | return temp | |
119 | ||
120 | decrypted_data = aes_ctr_decrypt(cipher, key, Counter()) | |
121 | plaintext = ''.join(map(lambda x: chr(x), decrypted_data)) | |
122 | ||
123 | return plaintext | |
124 | ||
125 | RCON = (0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36) | |
126 | SBOX = (0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76, | |
127 | 0xCA, 0x82, 0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 0x72, 0xC0, | |
128 | 0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15, | |
129 | 0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75, | |
130 | 0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84, | |
131 | 0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 0x6A, 0xCB, 0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF, | |
132 | 0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D, 0x33, 0x85, 0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8, | |
133 | 0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2, | |
134 | 0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 0xC4, 0xA7, 0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73, | |
135 | 0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 0x90, 0x88, 0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB, | |
136 | 0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79, | |
137 | 0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08, | |
138 | 0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A, | |
139 | 0x70, 0x3E, 0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1, 0x1D, 0x9E, | |
140 | 0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF, | |
141 | 0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16) | |
142 | MIX_COLUMN_MATRIX = ((2,3,1,1), | |
143 | (1,2,3,1), | |
144 | (1,1,2,3), | |
145 | (3,1,1,2)) | |
146 | ||
147 | def sub_bytes(data): | |
48ea9cea | 148 | return [SBOX[x] for x in data] |
f3bcebb1 | 149 | |
150 | def rotate(data): | |
151 | return data[1:] + [data[0]] | |
152 | ||
153 | def key_schedule_core(data, rcon_iteration): | |
154 | data = rotate(data) | |
155 | data = sub_bytes(data) | |
156 | data[0] = data[0] ^ RCON[rcon_iteration] | |
157 | ||
158 | return data | |
159 | ||
160 | def xor(data1, data2): | |
48ea9cea | 161 | return [x^y for x, y in zip(data1, data2)] |
f3bcebb1 | 162 | |
163 | def mix_column(data): | |
164 | data_mixed = [] | |
165 | for row in range(4): | |
166 | mixed = 0 | |
167 | for column in range(4): | |
168 | addend = data[column] | |
169 | if MIX_COLUMN_MATRIX[row][column] in (2,3): | |
170 | addend <<= 1 | |
171 | if addend > 0xff: | |
172 | addend &= 0xff | |
173 | addend ^= 0x1b | |
174 | if MIX_COLUMN_MATRIX[row][column] == 3: | |
175 | addend ^= data[column] | |
176 | mixed ^= addend & 0xff | |
177 | data_mixed.append(mixed) | |
178 | return data_mixed | |
179 | ||
180 | def mix_columns(data): | |
181 | data_mixed = [] | |
182 | for i in range(4): | |
183 | column = data[i*4 : (i+1)*4] | |
184 | data_mixed += mix_column(column) | |
185 | return data_mixed | |
186 | ||
187 | def shift_rows(data): | |
188 | data_shifted = [] | |
189 | for column in range(4): | |
190 | for row in range(4): | |
191 | data_shifted.append( data[((column + row) & 0b11) * 4 + row] ) | |
192 | return data_shifted | |
193 | ||
194 | def inc(data): | |
195 | data = data[:] # copy | |
196 | for i in range(len(data)-1,-1,-1): | |
197 | if data[i] == 255: | |
198 | data[i] = 0 | |
199 | else: | |
200 | data[i] = data[i] + 1 | |
201 | break | |
202 | return data |