# MIT License # Copyright (c) 2021 Or Gur Arie # Permission is hereby granted, free of charge, to any person obtaining a copy # of this software and associated documentation files (the "Software"), to deal # in the Software without restriction, including without limitation the rights # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell # copies of the Software, and to permit persons to whom the Software is # furnished to do so, subject to the following conditions: # The above copyright notice and this permission notice shall be included in all # copies or substantial portions of the Software. # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE # SOFTWARE. ## AES lookup tables # resource: https://en.wikipedia.org/wiki/Rijndael_S-box s_box = ( 0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76, 0xCA, 0x82, 0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 0x72, 0xC0, 0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15, 0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75, 0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84, 0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 0x6A, 0xCB, 0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF, 0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D, 0x33, 0x85, 0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8, 0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2, 0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 0xC4, 0xA7, 0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73, 0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 0x90, 0x88, 0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB, 0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79, 0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08, 0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A, 0x70, 0x3E, 0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1, 0x1D, 0x9E, 0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF, 0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16, ) inv_s_box = ( 0x52, 0x09, 0x6A, 0xD5, 0x30, 0x36, 0xA5, 0x38, 0xBF, 0x40, 0xA3, 0x9E, 0x81, 0xF3, 0xD7, 0xFB, 0x7C, 0xE3, 0x39, 0x82, 0x9B, 0x2F, 0xFF, 0x87, 0x34, 0x8E, 0x43, 0x44, 0xC4, 0xDE, 0xE9, 0xCB, 0x54, 0x7B, 0x94, 0x32, 0xA6, 0xC2, 0x23, 0x3D, 0xEE, 0x4C, 0x95, 0x0B, 0x42, 0xFA, 0xC3, 0x4E, 0x08, 0x2E, 0xA1, 0x66, 0x28, 0xD9, 0x24, 0xB2, 0x76, 0x5B, 0xA2, 0x49, 0x6D, 0x8B, 0xD1, 0x25, 0x72, 0xF8, 0xF6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xD4, 0xA4, 0x5C, 0xCC, 0x5D, 0x65, 0xB6, 0x92, 0x6C, 0x70, 0x48, 0x50, 0xFD, 0xED, 0xB9, 0xDA, 0x5E, 0x15, 0x46, 0x57, 0xA7, 0x8D, 0x9D, 0x84, 0x90, 0xD8, 0xAB, 0x00, 0x8C, 0xBC, 0xD3, 0x0A, 0xF7, 0xE4, 0x58, 0x05, 0xB8, 0xB3, 0x45, 0x06, 0xD0, 0x2C, 0x1E, 0x8F, 0xCA, 0x3F, 0x0F, 0x02, 0xC1, 0xAF, 0xBD, 0x03, 0x01, 0x13, 0x8A, 0x6B, 0x3A, 0x91, 0x11, 0x41, 0x4F, 0x67, 0xDC, 0xEA, 0x97, 0xF2, 0xCF, 0xCE, 0xF0, 0xB4, 0xE6, 0x73, 0x96, 0xAC, 0x74, 0x22, 0xE7, 0xAD, 0x35, 0x85, 0xE2, 0xF9, 0x37, 0xE8, 0x1C, 0x75, 0xDF, 0x6E, 0x47, 0xF1, 0x1A, 0x71, 0x1D, 0x29, 0xC5, 0x89, 0x6F, 0xB7, 0x62, 0x0E, 0xAA, 0x18, 0xBE, 0x1B, 0xFC, 0x56, 0x3E, 0x4B, 0xC6, 0xD2, 0x79, 0x20, 0x9A, 0xDB, 0xC0, 0xFE, 0x78, 0xCD, 0x5A, 0xF4, 0x1F, 0xDD, 0xA8, 0x33, 0x88, 0x07, 0xC7, 0x31, 0xB1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xEC, 0x5F, 0x60, 0x51, 0x7F, 0xA9, 0x19, 0xB5, 0x4A, 0x0D, 0x2D, 0xE5, 0x7A, 0x9F, 0x93, 0xC9, 0x9C, 0xEF, 0xA0, 0xE0, 0x3B, 0x4D, 0xAE, 0x2A, 0xF5, 0xB0, 0xC8, 0xEB, 0xBB, 0x3C, 0x83, 0x53, 0x99, 0x61, 0x17, 0x2B, 0x04, 0x7E, 0xBA, 0x77, 0xD6, 0x26, 0xE1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0C, 0x7D, ) ## AES AddRoundKey # Round constants https://en.wikipedia.org/wiki/AES_key_schedule#Round_constants r_con = ( 0x00, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1B, 0x36, 0x6C, 0xD8, 0xAB, 0x4D, 0x9A, 0x2F, 0x5E, 0xBC, 0x63, 0xC6, 0x97, 0x35, 0x6A, 0xD4, 0xB3, 0x7D, 0xFA, 0xEF, 0xC5, 0x91, 0x39, ) def add_round_key(s, k): for i in range(4): for j in range(4): s[i][j] ^= k[i][j] ## AES SubBytes def sub_bytes(s): for i in range(4): for j in range(4): s[i][j] = s_box[s[i][j]] def inv_sub_bytes(s): for i in range(4): for j in range(4): s[i][j] = inv_s_box[s[i][j]] ## AES ShiftRows def shift_rows(s): s[0][1], s[1][1], s[2][1], s[3][1] = s[1][1], s[2][1], s[3][1], s[0][1] s[0][2], s[1][2], s[2][2], s[3][2] = s[2][2], s[3][2], s[0][2], s[1][2] s[0][3], s[1][3], s[2][3], s[3][3] = s[3][3], s[0][3], s[1][3], s[2][3] def inv_shift_rows(s): s[0][1], s[1][1], s[2][1], s[3][1] = s[3][1], s[0][1], s[1][1], s[2][1] s[0][2], s[1][2], s[2][2], s[3][2] = s[2][2], s[3][2], s[0][2], s[1][2] s[0][3], s[1][3], s[2][3], s[3][3] = s[1][3], s[2][3], s[3][3], s[0][3] ## AES MixColumns # learned from http://cs.ucsb.edu/~koc/cs178/projects/JT/aes.c xtime = lambda a: (((a << 1) ^ 0x1B) & 0xFF) if (a & 0x80) else (a << 1) def mix_single_column(a): # see Sec 4.1.2 in The Design of Rijndael t = a[0] ^ a[1] ^ a[2] ^ a[3] u = a[0] a[0] ^= t ^ xtime(a[0] ^ a[1]) a[1] ^= t ^ xtime(a[1] ^ a[2]) a[2] ^= t ^ xtime(a[2] ^ a[3]) a[3] ^= t ^ xtime(a[3] ^ u) def mix_columns(s): for i in range(4): mix_single_column(s[i]) def inv_mix_columns(s): # see Sec 4.1.3 in The Design of Rijndael for i in range(4): u = xtime(xtime(s[i][0] ^ s[i][2])) v = xtime(xtime(s[i][1] ^ s[i][3])) s[i][0] ^= u s[i][1] ^= v s[i][2] ^= u s[i][3] ^= v mix_columns(s) ## AES Bytes def bytes2matrix(text): """ Converts a 16-byte array into a 4x4 matrix. """ return [list(text[i:i+4]) for i in range(0, len(text), 4)] def matrix2bytes(matrix): """ Converts a 4x4 matrix into a 16-byte array. """ return bytes(sum(matrix, [])) def xor_bytes(a, b): """ Returns a new byte array with the elements xor'ed. """ return bytes(i^j for i, j in zip(a, b)) def split_blocks(message, block_size=16, require_padding=True): assert len(message) % block_size == 0 or not require_padding return [message[i:i+16] for i in range(0, len(message), block_size)] class AES128: # AES-128 block size block_size = 16 # AES-128 encrypts messages with 10 rounds _rounds = 10 # initiate the AES objecy def __init__(self, key): """ Initializes the object with a given key. """ # make sure key length is right assert len(key) == AES128.block_size # ExpandKey self._round_keys = self._expand_key(key) # will perform the AES ExpandKey phase def _expand_key(self, master_key): """ Expands and returns a list of key matrices for the given master_key. """ # Initialize round keys with raw key material. key_columns = bytes2matrix(master_key) iteration_size = len(master_key) // 4 # Each iteration has exactly as many columns as the key material. i = 1 while len(key_columns) < (self._rounds + 1) * 4: # Copy previous word. word = list(key_columns[-1]) # Perform schedule_core once every "row". if len(key_columns) % iteration_size == 0: # Circular shift. word.append(word.pop(0)) # Map to S-BOX. word = [s_box[b] for b in word] # XOR with first byte of R-CON, since the others bytes of R-CON are 0. word[0] ^= r_con[i] i += 1 elif len(master_key) == 32 and len(key_columns) % iteration_size == 4: # Run word through S-box in the fourth iteration when using a # 256-bit key. word = [s_box[b] for b in word] # XOR with equivalent word from previous iteration. word = bytes(i^j for i, j in zip(word, key_columns[-iteration_size])) key_columns.append(word) # Group key words in 4x4 byte matrices. return [key_columns[4*i : 4*(i+1)] for i in range(len(key_columns) // 4)] # encrypt a single block of data with AES def _encrypt_block(self, plaintext): """ Encrypts a single block of 16 byte long plaintext. """ # length of a single block assert len(plaintext) == AES128.block_size # perform on a matrix state = bytes2matrix(plaintext) # AddRoundKey add_round_key(state, self._round_keys[0]) # 9 main rounds for i in range(1, self._rounds): # SubBytes sub_bytes(state) # ShiftRows shift_rows(state) # MixCols mix_columns(state) # AddRoundKey add_round_key(state, self._round_keys[i]) # last round, w/t AddRoundKey step sub_bytes(state) shift_rows(state) add_round_key(state, self._round_keys[-1]) # return the encrypted matrix as bytes return matrix2bytes(state) # decrypt a single block of data with AES def _decrypt_block(self, ciphertext): """ Decrypts a single block of 16 byte long ciphertext. """ # length of a single block assert len(ciphertext) == AES128.block_size # perform on a matrix state = bytes2matrix(ciphertext) # in reverse order, last round is first add_round_key(state, self._round_keys[-1]) inv_shift_rows(state) inv_sub_bytes(state) for i in range(self._rounds - 1, 0, -1): # nain rounds add_round_key(state, self._round_keys[i]) inv_mix_columns(state) inv_shift_rows(state) inv_sub_bytes(state) # initial AddRoundKey phase add_round_key(state, self._round_keys[0]) # return bytes return matrix2bytes(state) # will encrypt the entire data def encrypt(self, plaintext, iv): """ Encrypts `plaintext` using CBC mode and PKCS#7 padding, with the given initialization vector (iv). """ # iv length must be same as block size assert len(iv) == AES128.block_size assert len(plaintext) % AES128.block_size == 0 ciphertext_blocks = [] previous = iv for plaintext_block in split_blocks(plaintext): # in CBC mode every block is XOR'd with the previous block xorred = xor_bytes(plaintext_block, previous) # encrypt current block block = self._encrypt_block(xorred) previous = block # append to ciphertext ciphertext_blocks.append(block) # return as bytes return b''.join(ciphertext_blocks) # will decrypt the entire data def decrypt(self, ciphertext, iv): """ Decrypts `ciphertext` using CBC mode and PKCS#7 padding, with the given initialization vector (iv). """ # iv length must be same as block size assert len(iv) == AES128.block_size plaintext_blocks = [] previous = iv for ciphertext_block in split_blocks(ciphertext): # in CBC mode every block is XOR'd with the previous block xorred = xor_bytes(previous, self._decrypt_block(ciphertext_block)) # append plaintext plaintext_blocks.append(xorred) previous = ciphertext_block return b''.join(plaintext_blocks)