cipher.py

from typing import List
from config import *
from utils import *
import binascii

class NotToday(object):
    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]

    def __init__(self, key: bytes, mode: str):
        self.external_key = key
        self.mode = mode
        self.subkeys = self._key_scheduler(self.external_key, ROUND_NUM)
    
    def encrypt(self, plaintext: bytes) -> bytes:
        blocks = text_to_blocks(plaintext, BLOCK_SIZE)
        iv = b'\x00' * BLOCK_SIZE
        enc_blocks = []

        for i, block in enumerate(blocks):
            if self.mode == 'ECB':
                enc = self._feistel_net(block)
                enc_blocks.append(enc)
            elif self.mode == 'CBC':
                xorwith = iv if i == 0 else enc_blocks[-1]
                temp = xor_bytes(block, xorwith)
                enc = self._feistel_net(temp)
                enc_blocks.append(enc)
            elif self.mode == 'Counter':
                counter_block = counter_to_block(i)
                enc = self._feistel_net(counter_block)
                enc = xor_bytes(block, enc)
                enc_blocks.append(enc)
            else:
                raise Exception('Invalid mode of operation')
        
        return b''.join(enc_blocks)

    def decrypt(self, ciphertext: bytes) -> bytes:
        blocks = text_to_blocks(ciphertext, BLOCK_SIZE)
        iv = b'\x00' * BLOCK_SIZE
        dec_blocks = []

        for i, block in enumerate(blocks):
            if self.mode == 'ECB':
                temp = switch_half_blocks(block, BLOCK_SIZE)
                dec = self._feistel_net(temp, encrypt=False)
                dec = switch_half_blocks(dec, BLOCK_SIZE)
                dec_blocks.append(dec)
            elif self.mode == 'CBC':
                xorwith = iv if i == 0 else blocks[-1]
                temp = switch_half_blocks(block, BLOCK_SIZE)
                dec = self._feistel_net(temp, encrypt=False)
                dec = switch_half_blocks(dec, BLOCK_SIZE)
                dec = xor_bytes(dec, xorwith)
                dec_blocks.append(dec)
            elif self.mode == 'Counter':
                counter_block = counter_to_block(i)
                enc = self._feistel_net(counter_block)
                dec = xor_bytes(block, enc)
                dec_blocks.append(dec)
            else:
                raise Exception('Invalid mode of operation')
        
        return blocks_to_text(dec_blocks)

    def _feistel_net(self, block: bytes, encrypt: bool = True) -> bytes:
        total_length = len(block)
        half_length = total_length // 2
        l = block[:half_length]
        r = block[half_length:]

        for i in range(ROUND_NUM):
            subkey = self.subkeys[i] if encrypt else self.subkeys[ROUND_NUM - (i+1)]
            new_r = xor_bytes(l, self._f_function(r, subkey))
            l = r
            r = new_r

        return l + r

    def _f_function(self, half_block: bytes, round_key: bytes) -> bytes:
        temp = bytes()
        half_block_roll = half_block[0] % 8
        round_key_roll = round_key[0] % 8

        for i in range(8):
            new_value = roll_int_right(half_block[i], half_block_roll) ^ roll_int_right(round_key[i], round_key_roll)
            temp = temp + bytes([new_value])

        # S-Box substitution
        subs = bytes()
        for i in range(8):
            subs = subs + bytes([self.sbox[temp[i]]])

        return roll_bits_right(subs, subs[7] % 64)

    def _key_scheduler(self, external_key: bytes, round: int) -> List[bytes]:
        if len(external_key) * 8 != 192:
            raise Exception('Invalid key size')
            
        if round % 3 != 0:
            raise Exception('Invalid round number')

        keys = [external_key[i*8:(i+1)*8] for i in range(3)]

        for i in range(round//3):
            temp = []
            temp.append(roll_bits_right(xor_bytes(keys[-3], keys[-2]), i))
            temp.append(roll_bits_right(xor_bytes(keys[-3], keys[-1]), i+1))
            temp.append(roll_bits_right(xor_bytes(keys[-2], keys[-1]), i+2))
            keys.extend(temp)

        keys = keys[3:]
        return keys