Subversion Repositories aes-128-ecb-encoder

"""Tham module provides encrypting/decrypting according AES(128) standart.

Based on Rijndael algorithm, AES uses 4 transformation for encrypting: SubSytes(), ShiftRows(),

MixColumns() and AddRoundKey(). For decrypting it uses inverse functions of that fout.

Detales you can read here:

http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf

or here:

http://en.wikipedia.org/wiki/Advanced_Encryption_Standard

or here:

http://www.cs.bc.edu/~straubin/cs381-05/blockciphers/rijndael_ingles2004.swf

or somewhere else.

Comments rather won't help if don't read documentation of the algorithm.

"""

nb = 4  # number of coloumn of State (for AES = 4)

nr = 10  # number of rounds ib ciper cycle (if nb = 4 nr = 10)

nk = 4  # the key length (in 32-bit words)

# This dict will be used in SubBytes(). 

hex_symbols_to_int = {'a': 10, 'b': 11, 'c': 12, 'd': 13, 'e': 14, 'f': 15}

sbox = [

    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_sbox = [

    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

]

rcon = [[0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36],

        [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00],

        [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00],

        [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]

]

def print_list(info_string, state):

    """Function prints state

    """

    print(info_string)

    for row in state:

        print('[{}]'.format(', '.join(hex(element) for element in row)))

    print('----')

    return 0

def encrypt(input_bytes, key):

    """Function encrypts the input_bytes according to AES(128) algorithm using the key

    Args:

       input_bytes -- list of int less than 255, ie list of bytes. Length of input_bytes is constantly 16

       key -- a strig of plain text. Do not forget it! The same string is used in decryption

    Returns:

        List of int

    """

    # let's prepare our enter data: State array and KeySchedule

    state = [[] for j in range(4)]

    for r in range(4):

        for c in range(nb):

            state[r].append(input_bytes[r + 4 * c])

    key_schedule = key_expansion(key)

    print_list('Initial state:', state);

    state = add_round_key(state, key_schedule)

    print_list('After add round key:', state)

    for rnd in range(1, nr):

        print ('===Round: ===', rnd)

        state = sub_bytes(state)

        print_list('After sub bytes:', state)

        state = shift_rows(state)

        print_list('After shift rows:', state)

        state = mix_columns(state)

        print_list('After mix columns:', state)

        state = add_round_key(state, key_schedule, rnd)

        print_list('After add round key:', state)

    print ('===Final round: ===')

    state = sub_bytes(state)

    print_list('After sub bytes:', state)

    state = shift_rows(state)

    print_list('After shift rows:', state)

    state = add_round_key(state, key_schedule, rnd + 1)

    print_list('After add round key:', state)

    output = [None for i in range(4 * nb)]

    for r in range(4):

        for c in range(nb):

            output[r + 4 * c] = state[r][c]

    return output

def decrypt(cipher, key):

    """Function decrypts the cipher according to AES(128) algorithm using the key

    Args:

       cipher -- list of int less than 255, ie list of bytes

       key -- a strig of plain text. Do not forget it! The same string is used in decryption

    Returns:

        List of int

    """

    # let's prepare our algorithm enter data: State array and KeySchedule

    state = [[] for i in range(nb)]

    for r in range(4):

        for c in range(nb):

            state[r].append(cipher[r + 4 * c])

    key_schedule = key_expansion(key)

    state = add_round_key(state, key_schedule, nr)

    rnd = nr - 1

    while rnd >= 1:

        state = shift_rows(state, inv=True)

        state = sub_bytes(state, inv=True)

        state = add_round_key(state, key_schedule, rnd)

        state = mix_columns(state, inv=True)

        rnd -= 1

    state = shift_rows(state, inv=True)

    state = sub_bytes(state, inv=True)

    state = add_round_key(state, key_schedule, rnd)

    output = [None for i in range(4 * nb)]

    for r in range(4):

        for c in range(nb):

            output[r + 4 * c] = state[r][c]

    return output

def sub_bytes(state, inv=False):

    """That transformation replace every element from State on element from Sbox

    according the algorithm: in hexadecimal notation an element from State

    consist of two values: 0x<val1><val2>. We take elem from crossing

    val1-row and val2-column in Sbox and put it instead of the element in State.

    If decryption-transformation is on (inv == True) it uses InvSbox instead Sbox.

    Args:

        inv -- If value == False means function is encryption-transformation.

               True - decryption-transformation

    """

    if inv == False:  # encrypt

        box = sbox

    else:  # decrypt

        box = inv_sbox

    for i in range(len(state)):

        for j in range(len(state[i])):

            row = state[i][j] // 0x10

            col = state[i][j] % 0x10

            # Our Sbox is a flat array, not a bable. So, we use this trich to find elem:

            # And DO NOT change list sbox! if you want it to work

            box_elem = box[16 * row + col]

            state[i][j] = box_elem

    return state

def shift_rows(state, inv=False):

    """That transformation shifts rows of State: the second rotate over 1 bytes,

    the third rotate over 2 bytes, the fourtg rotate over 3 bytes. The transformation doesn't

    touch the first row. When encrypting transformation uses left shift, in decription - right shift

    Args:

        inv: If value == False means function is encryption mode. True - decryption mode

    """

    count = 1

    if inv == False:  # encrypting

        for i in range(1, nb):

            state[i] = left_shift(state[i], count)

            count += 1

    else:  # decryptionting

        for i in range(1, nb):

            state[i] = right_shift(state[i], count)

            count += 1

    return state

def mix_columns(state, inv=False):

    """When encrypting transformation multiplyes every column of State with

    a fixed polinomial a(x) = {03}x**3 + {01}x**2 + {01}x + {02} in Galua field.

    When decrypting multiplies with a'(x) = {0b}x**3 + {0d}x**2 + {09}x + {0e}

    Detailed information in AES standart.

    Args:

        inv: If value == False means function is encryption mode. True - decryption mode

    """

    for i in range(nb):

        if inv == False:  # encryption

            s0 = mul_by_02(state[0][i]) ^ mul_by_03(state[1][i]) ^ state[2][i] ^ state[3][i]

            s1 = state[0][i] ^ mul_by_02(state[1][i]) ^ mul_by_03(state[2][i]) ^ state[3][i]

            s2 = state[0][i] ^ state[1][i] ^ mul_by_02(state[2][i]) ^ mul_by_03(state[3][i])

            s3 = mul_by_03(state[0][i]) ^ state[1][i] ^ state[2][i] ^ mul_by_02(state[3][i])

        else:  # decryption

            s0 = mul_by_0e(state[0][i]) ^ mul_by_0b(state[1][i]) ^ mul_by_0d(state[2][i]) ^ mul_by_09(state[3][i])

            s1 = mul_by_09(state[0][i]) ^ mul_by_0e(state[1][i]) ^ mul_by_0b(state[2][i]) ^ mul_by_0d(state[3][i])

            s2 = mul_by_0d(state[0][i]) ^ mul_by_09(state[1][i]) ^ mul_by_0e(state[2][i]) ^ mul_by_0b(state[3][i])

            s3 = mul_by_0b(state[0][i]) ^ mul_by_0d(state[1][i]) ^ mul_by_09(state[2][i]) ^ mul_by_0e(state[3][i])

        state[0][i] = s0

        state[1][i] = s1

        state[2][i] = s2

        state[3][i] = s3

    return state

def key_expansion(key):

    """It makes list of RoundKeys for function AddRoundKey. All details

    about algorithm is is in AES standart

    """

    #key_symbols = [ord(symbol) for symbol in key]

    key_symbols = key

    # ChipherKey shoul contain 16 symbols to fill 4*4 table. If it's less

    # complement the key with "0x01"

    if len(key_symbols) < 4 * nk:

        for i in range(4 * nk - len(key_symbols)):

            key_symbols.append(0x01)

    # make ChipherKey(which is base of KeySchedule)

    key_schedule = [[] for i in range(4)]

    for r in range(4):

        for c in range(nk):

            key_schedule[r].append(key_symbols[r + 4 * c])

    # Comtinue to fill KeySchedule

    for col in range(nk, nb * (nr + 1)):  # col - column number

        if col % nk == 0:

            # take shifted (col - 1)th column...

            tmp = [key_schedule[row][col - 1] for row in range(1, 4)]

            tmp.append(key_schedule[0][col - 1])

            # change its elements using Sbox-table like in SubBytes...

            for j in range(len(tmp)):

                sbox_row = tmp[j] // 0x10

                sbox_col = tmp[j] % 0x10

                sbox_elem = sbox[16 * sbox_row + sbox_col]

                tmp[j] = sbox_elem

            # and finally make XOR of 3 columns

            for row in range(4):

                s = (key_schedule[row][col - 4]) ^ (tmp[row]) ^ (rcon[row][int(col / nk - 1)])

                key_schedule[row].append(s)

        else:

            # just make XOR of 2 columns

            for row in range(4):

                s = key_schedule[row][col - 4] ^ key_schedule[row][col - 1]

                key_schedule[row].append(s)

    return key_schedule

def add_round_key(state, key_schedule, round=0):

    """That transformation combines State and KeySchedule together. Xor

    of State and RoundSchedule(part of KeySchedule).

    """

    for col in range(nk):

        # nb*round is a shift which indicates start of a part of the KeySchedule

        s0 = state[0][col] ^ key_schedule[0][nb * round + col]

        s1 = state[1][col] ^ key_schedule[1][nb * round + col]

        s2 = state[2][col] ^ key_schedule[2][nb * round + col]

        s3 = state[3][col] ^ key_schedule[3][nb * round + col]

        state[0][col] = s0

        state[1][col] = s1

        state[2][col] = s2

        state[3][col] = s3

    return state

# Small helpful functions block

def left_shift(array, count):

    """Rotate the array over count times"""

    res = array[:]

    for i in range(count):

        temp = res[1:]

        temp.append(res[0])

        res[:] = temp[:]

    return res

def right_shift(array, count):

    """Rotate the array over count times"""

    res = array[:]

    for i in range(count):

        tmp = res[:-1]

        tmp.insert(0, res[-1])

        res[:] = tmp[:]

    return res

def mul_by_02(num):

    """The function multiplies by 2 in Galua space"""

    if num < 0x80:

        res = (num << 1)

    else:

        res = (num << 1) ^ 0x1b

    return res % 0x100

def mul_by_03(num):

    """The function multiplies by 3 in Galua space

    example: 0x03*num = (0x02 + 0x01)num = num*0x02 + num

    Addition in Galua field is oparetion XOR

    """

    return (mul_by_02(num) ^ num)

def mul_by_09(num):

    # return mul_by_03(num)^mul_by_03(num)^mul_by_03(num) - works wrong, I don't know why

    return mul_by_02(mul_by_02(mul_by_02(num))) ^ num

def mul_by_0b(num):

    # return mul_by_09(num)^mul_by_02(num)

    return mul_by_02(mul_by_02(mul_by_02(num))) ^ mul_by_02(num) ^ num

def mul_by_0d(num):

    # return mul_by_0b(num)^mul_by_02(num)

    return mul_by_02(mul_by_02(mul_by_02(num))) ^ mul_by_02(mul_by_02(num)) ^ num

def mul_by_0e(num):

    # return mul_by_0d(num)^num

    return mul_by_02(mul_by_02(mul_by_02(num))) ^ mul_by_02(mul_by_02(num)) ^ mul_by_02(num)

# End of small helpful functions block