def pad_plaintext(plaintext):
    while len(plaintext) < 8:
        plaintext += "@"
    return plaintext[:8]

def text_to_binary(text):
    binary_text = ""
    for char in text:
        binary_char = bin(ord(char))[2:].zfill(8)
        binary_text += binary_char
    return binary_text

def split_blocks(plaintext):
    blocks = []
    while len(plaintext) > 0:
        blocks.append(plaintext[:8])
        plaintext = plaintext[8:]
    return blocks

def ascii_to_binary_key(key):
    binary_key = ""
    for char in key:
        binary_key += format(ord(char), '08b')
    return binary_key

def apply_key_permutation(binary_key, permutation_table):
    permuted_key = ""
    for index in permutation_table:
        permuted_key += binary_key[index - 1]
    return permuted_key

def generate_subkeys(key):
    pc_1_table = [57, 49, 41, 33, 25, 17, 9,
                  1, 58, 50, 42, 34, 26, 18,
                  10, 2, 59, 51, 43, 35, 27,
                  19, 11, 3, 60, 52, 44, 36,
                  63, 55, 47, 39, 31, 23, 15,
                  7, 62, 54, 46, 38, 30, 22,
                  14, 6, 61, 53, 45, 37, 29,
                  21, 13, 5, 28, 20, 12, 4]

    pc_2_table = [14, 17, 11, 24, 1, 5,
                  3, 28, 15, 6, 21, 10,
                  23, 19, 12, 4, 26, 8,
                  16, 7, 27, 20, 13, 2,
                  41, 52, 31, 37, 47, 55,
                  30, 40, 51, 45, 33, 48,
                  44, 49, 39, 56, 34, 53,
                  46, 42, 50, 36, 29, 32]

    if len(key) != 8:
        raise ValueError("Key size must be 8 characters.")

    binary_key = ascii_to_binary_key(key)

    permuted_key = apply_key_permutation(binary_key, pc_1_table)

    # Convert key to numeric value
    permuted_key = int(permuted_key, 2)

    subkeys = []

    # Generate subkeys for each round
    for round in range(1, 17):
        # Left shifts for left half and right half of the key
        left_shifts = 1 if round in [1, 2, 9, 16] else 2
        permuted_key = ((permuted_key << left_shifts) & 0xFFFFFFFFFFFF) | (permuted_key >> (28 - left_shifts))

        # Use PC-2 table to convert the key to a 48-bit subkey
        subkey = apply_key_permutation(bin(permuted_key)[2:].zfill(56), pc_2_table)
        subkeys.append(subkey)

    return subkeys

def initial_permutation(block):
    # Perform initial permutation on the block
    initial_permutation_table = [58, 50, 42, 34, 26, 18, 10, 2,
                                 60, 52, 44, 36, 28, 20, 12, 4,
                                 62, 54, 46, 38, 30, 22, 14, 6,
                                 64, 56, 48, 40, 32, 24, 16, 8,
                                 57, 49, 41, 33, 25, 17, 9, 1,
                                 59, 51, 43, 35, 27, 19, 11, 3,
                                 61, 53, 45, 37, 29, 21, 13, 5,
                                 63, 55, 47, 39, 31, 23, 15, 7]

    permuted_block = ""
    for index in initial_permutation_table:
        permuted_block += block[index - 1]
    return permuted_block

def expand_permutation(block):
    # Perform expansion permutation on the block
    expansion_table = [32, 1, 2, 3, 4, 5, 4, 5,
                       6, 7, 8, 9, 8, 9, 10, 11,
                       12, 13, 12, 13, 14, 15, 16, 17,
                       16, 17, 18, 19, 20, 21, 20, 21,
                       22, 23, 24, 25, 24, 25, 26, 27,
                       28, 29, 28, 29, 30, 31, 32, 1]

    expanded_block = ""
    for index in expansion_table:
        expanded_block += block[index - 1]
    return expanded_block

def substitute(s_box_input, s_box_index):
    s_boxes = [
        # S1
        [
            [14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7],
            [0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8],
            [4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0],
            [15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13]
        ]
   ]
    row = int(s_box_input[0] + s_box_input[3], 2)
    column = int(s_box_input[1:3], 2)
    value = s_boxes[s_box_index][row][column]
    return bin(value)[2:].zfill(4)error in line 96 permuted _block +=block [index-1]