使用 Python 实现 DES 算法

des.py

from itertools import chain
from typing import List, Tuple

from .tables import *


class DES:
    def __init__(self, key: [str, bytes]):
        if isinstance(key, str):
            key = key.encode()
        if len(key) > 8:
            key = key[8:]
        elif len(key) < 8:
            key += b"".join(b"\x00" for _ in range(8 - len(key)))
        key_bit_list = self._bytes_to_bit_list(key)
        left_half_key_block = self._transform(key_bit_list, pc1_left_table)
        right_half_key_block = self._transform(key_bit_list, pc1_right_table)
        sub_key_list = []
        for round_index in range(16):
            left_half_key_block = self._circle_left_shift(left_half_key_block, key_left_shift_bits[round_index])
            right_half_key_block = self._circle_left_shift(right_half_key_block, key_left_shift_bits[round_index])
            sub_key_list.append(self._transform(left_half_key_block + right_half_key_block, pc2_table))
        self._sub_key_list = sub_key_list

    def encrypt(self, plain_text: [str, bytes]):
        if isinstance(plain_text, str):
            plain_text = plain_text.encode()
        plain_text_len = len(plain_text)
        if plain_text_len % 8:
            plain_text += b"".join(b"\x00" for _ in range(8 - plain_text_len % 8))
        encrypted_blocks = []
        for block in map(lambda s: plain_text[s:s + 8], range(0, plain_text_len, 8)):
            encrypted_blocks.append(self._encrypt_block(self._bytes_to_bit_list(block)))
        encrypted_bit_list = list(chain(*encrypted_blocks))
        return self._bit_list_to_bytes(encrypted_bit_list)

    def decrypt(self, cipher_text: bytes) -> str:
        self._sub_key_list.reverse()
        plain_text = self.encrypt(cipher_text)
        self._sub_key_list.reverse()
        return plain_text.decode().rstrip('\0')

    def _encrypt_block(self, plain_block: List[int]) -> List[int]:
        plain_block = self._transform(plain_block, ip_table)
        left_half_block = plain_block[:32]
        right_half_block = plain_block[32:]
        for round_index in range(16):
            left_half_block, right_half_block = right_half_block, \
                                                self._bit_list_xor(
                                                    left_half_block,
                                                    self._transform(
                                                        self._s_box_transform(
                                                            self._bit_list_xor(
                                                                self._transform(right_half_block,
                                                                                extend_table),
                                                                self._sub_key_list[round_index]
                                                            )
                                                        ), p_table
                                                    )
                                                )
        return self._transform(right_half_block + left_half_block, fp_table)

    @staticmethod
    def _transform(raw_list: list, transform_table: List[int]) -> list:
        return list(map(lambda index: raw_list[index], transform_table))

    @staticmethod
    def _bytes_to_bit_list(input_bytes: bytes) -> List[int]:
        bit_list = [0] * 8 * len(input_bytes)
        index = 0
        for char_ascii in input_bytes:
            loc = 7
            while loc >= 0:
                bit_list[index] = 0 if char_ascii & (1 << loc) == 0 else 1
                loc -= 1
                index += 1
        return bit_list

    @staticmethod
    def _bit_list_to_bytes(bit_list: List[int]) -> bytes:
        char_ascii = 0
        byte_list = []
        for index, bit in enumerate(bit_list):
            char_ascii += bit << (7 - index % 8)
            if index % 8 == 7:
                byte_list.append(char_ascii)
                char_ascii = 0
        return bytes(byte_list)

    @staticmethod
    def _circle_left_shift(input_list: list, bits: int) -> list:
        return input_list[bits:] + input_list[:bits]

    @staticmethod
    def _bit_list_xor(left: list, right: list) -> List[str]:
        return list(map(lambda x, y: x ^ y, left, right))

    @staticmethod
    def _s_box_transform(input_list: list) -> list:
        transformed = [0 for _ in range(32)]
        transformed_index = 0
        r = 0
        while r < 48:
            m = (input_list[r] << 1) + input_list[r + 5]
            n = (input_list[r + 1] << 3) + (input_list[r + 2] << 2) + (input_list[r + 3] << 1) + (input_list[r + 4])
            s_value = s_box_tables[r // 6][(m << 4) + n]
            transformed[transformed_index] = (s_value & 8) >> 3
            transformed[transformed_index + 1] = (s_value & 4) >> 2
            transformed[transformed_index + 2] = (s_value & 2) >> 1
            transformed[transformed_index + 3] = s_value & 1
            r += 6
            transformed_index += 4
        return transformed

tables.py

ip_table = [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,
            56, 48, 40, 32, 24, 16, 8, 0,
            58, 50, 42, 34, 26, 18, 10, 2,
            60, 52, 44, 36, 28, 20, 12, 4,
            62, 54, 46, 38, 30, 22, 14, 6]

fp_table = [39, 7, 47, 15, 55, 23, 63, 31,
            38, 6, 46, 14, 54, 22, 62, 30,
            37, 5, 45, 13, 53, 21, 61, 29,
            36, 4, 44, 12, 52, 20, 60, 28,
            35, 3, 43, 11, 51, 19, 59, 27,
            34, 2, 42, 10, 50, 18, 58, 26,
            33, 1, 41, 9, 49, 17, 57, 25,
            32, 0, 40, 8, 48, 16, 56, 24]

extend_table = [31, 0, 1, 2, 3, 4,
                3, 4, 5, 6, 7, 8,
                7, 8, 9, 10, 11, 12,
                11, 12, 13, 14, 15, 16,
                15, 16, 17, 18, 19, 20,
                19, 20, 21, 22, 23, 24,
                23, 24, 25, 26, 27, 28,
                27, 28, 29, 30, 31, 0]

pc1_left_table = [56, 48, 40, 32, 24, 16, 8,
                  0, 57, 49, 41, 33, 25, 17,
                  9, 1, 58, 50, 42, 34, 26,
                  18, 10, 2, 59, 51, 43, 35]

pc1_right_table = [62, 54, 46, 38, 30, 22, 14,
                   6, 61, 53, 45, 37, 29, 21,
                   13, 5, 60, 52, 44, 36, 28,
                   20, 12, 4, 27, 19, 11, 3]

pc2_table = [13, 16, 10, 23, 0, 4,
             2, 27, 14, 5, 20, 9,
             22, 18, 11, 3, 25, 7,
             15, 6, 26, 19, 12, 1,
             40, 51, 30, 36, 46, 54,
             29, 39, 50, 44, 32, 47,
             43, 48, 38, 55, 33, 52,
             45, 41, 49, 35, 28, 31]

key_left_shift_bits = [1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1]

p_table = [15, 6, 19, 20,
           28, 11, 27, 16,
           0, 14, 22, 25,
           4, 17, 30, 9,
           1, 7, 23, 13,
           31, 26, 2, 8,
           18, 12, 29, 5,
           21, 10, 3, 24]

s_box_tables = [[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],
                [15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10,
                 3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5,
                 0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15,
                 13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9],
                [10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8,
                 13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1,
                 13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7,
                 1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12,
                 ],
                [7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15,
                 13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9,
                 10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4,
                 3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14],
                [2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9,
                 14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6,
                 4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14,
                 11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3],
                [12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11,
                 10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8,
                 9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6,
                 4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13],
                [4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1,
                 13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6,
                 1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2,
                 6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12],
                [13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7,
                 1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2,
                 7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8,
                 2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11]]