AES_core.py

def sub_bytes(state):
    """
    SubBytes step in AES. Non-linear substitution step where each byte is replaced with another according to a lookup table.
    For simplicity, using a dummy S-box which just returns the byte itself (no real substitution).
    """
    return state  # Placeholder for the actual substitution using S-box.

def shift_rows(state):
    """
    ShiftRows step in AES. Cyclically shift the bytes in each row to the left; different shifts for each row.
    For simplicity, assuming the state is a list of four rows, each row is also a list of four bytes.
    """
    state[1] = state[1][1:] + state[1][:1]  # Row 1: Shift left by 1
    state[2] = state[2][2:] + state[2][:2]  # Row 2: Shift left by 2
    state[3] = state[3][3:] + state[3][:3]  # Row 3: Shift left by 3
    return state

def mix_columns(state):
    """
    MixColumns step in AES. Columns are mixed using a fixed polynomial represented as a matrix.
    For simplicity, this function performs a dummy operation which just returns the state unchanged.
    """
    return state  # Placeholder for the actual MixColumns operation.

def add_round_key(state, round_key):
    """
    AddRoundKey step in AES. Each byte of the state is combined with the round key using bitwise XOR.
    """
    for i in range(4):
        for j in range(4):
            state[i][j] ^= round_key[i][j]
    return state

# Example state and round key for testing the functions
state_example = [
    [0x32, 0x88, 0x31, 0xe0],
    [0x43, 0x5a, 0x31, 0x37],
    [0xf6, 0x30, 0x98, 0x07],
    [0xa8, 0x8d, 0xa2, 0x34]
]
round_key_example = [
    [0x2b, 0x28, 0xab, 0x09],
    [0x7e, 0xae, 0xf7, 0xcf],
    [0x15, 0xd2, 0x15, 0x4f],
    [0x16, 0xa6, 0x88, 0x3c]
]

# Apply each function
state_subbed = sub_bytes(state_example)
state_shifted = shift_rows(state_subbed)
state_mixed = mix_columns(state_shifted)
state_rounded = add_round_key(state_mixed, round_key_example)

state_rounded  # Output the final state after one round