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__all__ = ['aes_encrypt', 'key_expansion', 'aes_ctr_decrypt', 'aes_decrypt_text'] |
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import base64 |
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from math import ceil |
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BLOCK_SIZE_BYTES = 16 |
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def aes_ctr_decrypt(data, key, counter): |
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""" |
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Decrypt with aes in counter mode |
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@param {int[]} data cipher |
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@param {int[]} key 16/24/32-Byte cipher key |
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@param {instance} counter Instance whose next_value function (@returns {int[]} 16-Byte block) |
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returns the next counter block |
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@returns {int[]} decrypted data |
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""" |
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expanded_key = key_expansion(key) |
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block_count = int(ceil(float(len(data)) / BLOCK_SIZE_BYTES)) |
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decrypted_data=[] |
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for i in range(block_count): |
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counter_block = counter.next_value() |
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block = data[i*BLOCK_SIZE_BYTES : (i+1)*BLOCK_SIZE_BYTES] |
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block += [0]*(BLOCK_SIZE_BYTES - len(block)) |
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cipher_counter_block = aes_encrypt(counter_block, expanded_key) |
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decrypted_data += xor(block, cipher_counter_block) |
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decrypted_data = decrypted_data[:len(data)] |
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return decrypted_data |
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def key_expansion(data): |
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""" |
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Generate key schedule |
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@param {int[]} data 16/24/32-Byte cipher key |
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@returns {int[]} 176/208/240-Byte expanded key |
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""" |
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data = data[:] # copy |
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rcon_iteration = 1 |
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key_size_bytes = len(data) |
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expanded_key_size_bytes = (key_size_bytes/4 + 7) * BLOCK_SIZE_BYTES |
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while len(data) < expanded_key_size_bytes: |
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temp = data[-4:] |
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temp = key_schedule_core(temp, rcon_iteration) |
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rcon_iteration += 1 |
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data += xor(temp, data[-key_size_bytes : 4-key_size_bytes]) |
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for _ in range(3): |
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temp = data[-4:] |
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data += xor(temp, data[-key_size_bytes : 4-key_size_bytes]) |
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if key_size_bytes == 32: |
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temp = data[-4:] |
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temp = sub_bytes(temp) |
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data += xor(temp, data[-key_size_bytes : 4-key_size_bytes]) |
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for _ in range(3 if key_size_bytes == 32 else 2 if key_size_bytes == 24 else 0): |
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temp = data[-4:] |
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data += xor(temp, data[-key_size_bytes : 4-key_size_bytes]) |
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data = data[:expanded_key_size_bytes] |
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return data |
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def aes_encrypt(data, expanded_key): |
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""" |
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Encrypt one block with aes |
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@param {int[]} data 16-Byte state |
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@param {int[]} expanded_key 176/208/240-Byte expanded key |
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@returns {int[]} 16-Byte cipher |
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""" |
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rounds = len(expanded_key) / BLOCK_SIZE_BYTES - 1 |
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data = xor(data, expanded_key[:BLOCK_SIZE_BYTES]) |
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for i in range(1, rounds+1): |
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data = sub_bytes(data) |
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data = shift_rows(data) |
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if i != rounds: |
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data = mix_columns(data) |
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data = xor(data, expanded_key[i*BLOCK_SIZE_BYTES : (i+1)*BLOCK_SIZE_BYTES]) |
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return data |
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def aes_decrypt_text(data, password, key_size_bytes): |
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""" |
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Decrypt text |
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- The first 8 Bytes of decoded 'data' are the 8 high Bytes of the counter |
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- The cipher key is retrieved by encrypting the first 16 Byte of 'password' |
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with the first 'key_size_bytes' Bytes from 'password' (if necessary filled with 0's) |
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- Mode of operation is 'counter' |
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@param {str} data Base64 encoded string |
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@param {str,unicode} password Password (will be encoded with utf-8) |
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@param {int} key_size_bytes Possible values: 16 for 128-Bit, 24 for 192-Bit or 32 for 256-Bit |
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@returns {str} Decrypted data |
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""" |
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NONCE_LENGTH_BYTES = 8 |
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data = map(lambda c: ord(c), base64.b64decode(data)) |
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password = map(lambda c: ord(c), password.encode('utf-8')) |
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key = password[:key_size_bytes] + [0]*(key_size_bytes - len(password)) |
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key = aes_encrypt(key[:BLOCK_SIZE_BYTES], key_expansion(key)) * (key_size_bytes / BLOCK_SIZE_BYTES) |
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nonce = data[:NONCE_LENGTH_BYTES] |
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cipher = data[NONCE_LENGTH_BYTES:] |
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class Counter: |
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__value = nonce + [0]*(BLOCK_SIZE_BYTES - NONCE_LENGTH_BYTES) |
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def next_value(self): |
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temp = self.__value |
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self.__value = inc(self.__value) |
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return temp |
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decrypted_data = aes_ctr_decrypt(cipher, key, Counter()) |
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plaintext = ''.join(map(lambda x: chr(x), decrypted_data)) |
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return plaintext |
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RCON = (0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36) |
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SBOX = (0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76, |
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0xCA, 0x82, 0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 0x72, 0xC0, |
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0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15, |
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0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75, |
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0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84, |
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0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 0x6A, 0xCB, 0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF, |
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0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D, 0x33, 0x85, 0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8, |
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0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2, |
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0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 0xC4, 0xA7, 0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73, |
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0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 0x90, 0x88, 0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB, |
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0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79, |
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0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08, |
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0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A, |
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0x70, 0x3E, 0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1, 0x1D, 0x9E, |
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0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF, |
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0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16) |
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MIX_COLUMN_MATRIX = ((2,3,1,1), |
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(1,2,3,1), |
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(1,1,2,3), |
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(3,1,1,2)) |
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def sub_bytes(data): |
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return map(lambda x: SBOX[x], data) |
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def rotate(data): |
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return data[1:] + [data[0]] |
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def key_schedule_core(data, rcon_iteration): |
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data = rotate(data) |
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data = sub_bytes(data) |
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data[0] = data[0] ^ RCON[rcon_iteration] |
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return data |
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def xor(data1, data2): |
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return map(lambda (x,y): x^y, zip(data1, data2)) |
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def mix_column(data): |
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data_mixed = [] |
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for row in range(4): |
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mixed = 0 |
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for column in range(4): |
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addend = data[column] |
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if MIX_COLUMN_MATRIX[row][column] in (2,3): |
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addend <<= 1 |
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if addend > 0xff: |
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addend &= 0xff |
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addend ^= 0x1b |
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if MIX_COLUMN_MATRIX[row][column] == 3: |
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addend ^= data[column] |
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mixed ^= addend & 0xff |
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data_mixed.append(mixed) |
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return data_mixed |
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def mix_columns(data): |
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data_mixed = [] |
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for i in range(4): |
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column = data[i*4 : (i+1)*4] |
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data_mixed += mix_column(column) |
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return data_mixed |
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def shift_rows(data): |
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data_shifted = [] |
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for column in range(4): |
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for row in range(4): |
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data_shifted.append( data[((column + row) & 0b11) * 4 + row] ) |
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return data_shifted |
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def inc(data): |
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data = data[:] # copy |
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for i in range(len(data)-1,-1,-1): |
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if data[i] == 255: |
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data[i] = 0 |
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else: |
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data[i] = data[i] + 1 |
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break |
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return data |