密码学|DES

DES的数据来源
https://csrc.nist.gov/files/pubs/fips/46-3/final/docs/fips46-3.pdf

"""
置换表
此处下标从0开始，故为标准表每值减一
"""
IP = [
    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
]

#IP^{-1}
IP_INV = [
    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
]

E = [
    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
]
"""
将64位原始密钥通过PC-1置换表转换为56位
去除了每个字节的奇偶校验位
"""
PC1 = [
    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,
    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
]
"""
将循环左移得到的56位数据通过PC-2表转换为48位密钥K1
"""
PC2 = [
    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
]
"""
循环左移
将56位的密钥分为左右两部分(都为28位)
通过移位次数表得到C1和D1
再将C1和D1拼接到一起
"""
SHIFT_SCHEDULE = [
    1, 1, 2, 2, 2, 2, 2, 2,
    1, 2, 2, 2, 2, 2, 2, 1
]

P = [
    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盒
"""
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]
    ],
    # S2
    [
        [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]
    ],
    # S3
    [
        [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]
    ],
    # S4
    [
        [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]
    ],
    # S5
    [
        [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]
    ],
    # S6
    [
        [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]
    ],
    # S7
    [
        [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]
    ],
    # S8
    [
        [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]
    ]
]

def hex_to_bits(hex_str: str) -> list:
    """
    8字节转64bit
    密钥
    """
    if len(hex_str) != 16:
        raise ValueError
    key_bytes = bytes.fromhex(hex_str)
    return [int(bit) for byte in key_bytes for bit in f"{byte:08b}"]

def str_to_gb2312_bits(text: str) -> list:
    """GB2312编码"""
    try:
        gb_bytes = text.encode('gb2312')
    except UnicodeEncodeError as e:
        raise ValueError(f"GB2312编码失败: {e}")
    return [int(bit) for byte in gb_bytes for bit in f"{byte:08b}"]

def bits_to_gb2312_str(bits: list) -> str:
    """二进制GB2312解码（填充）"""
    byte_list = []
    for i in range(0, len(bits), 8):
        byte_bits = bits[i:i+8]
        if len(byte_bits) < 8:
            byte_bits += [0] * (8 - len(byte_bits))  # 补足8位
        byte = int(''.join(map(str, byte_bits)), 2)
        byte_list.append(byte)
    try:
        return bytes(byte_list).decode('gb2312', errors='replace')
    except UnicodeDecodeError:
        return bytes(byte_list).decode('gb2312', errors='ignore')

def pad_ecb(bits: list) -> list:
    """ECB模式填充：PKCS#7风格（填充长度值，如缺3位则填3个1）"""
    pad_len = 64 - (len(bits) % 64)
    if pad_len == 0:
        pad_len = 64  # 全填充块
    padding = [1 if i == pad_len -1 else 0 for i in range(pad_len)]  
    return bits + padding

def unpad_ecb(bits: list) -> list:
    """去除ECB填充（PKCS#7填充）"""
    # 查找最后一个1的位置，确定填充长度
    pad_bit = 1
    pad_index = len(bits) - 1
    while pad_index >= 0 and bits[pad_index] != pad_bit:
        pad_index -= 1
    if pad_index == -1:
        return bits  
    pad_len = len(bits) - pad_index
    return bits[:pad_index - pad_len +1]

def apply_permutation(bits, table):
    return [bits[i] for i in table]

def generate_subkeys(master_key):
    key_bits = apply_permutation(master_key, PC1)
    c = key_bits[:28]
    d = key_bits[28:]
    
    subkeys = []
    for shift in SHIFT_SCHEDULE:
        # 循环左移
        c = c[shift:] + c[:shift]
        d = d[shift:] + d[:shift]
        subkey = apply_permutation(c + d, PC2)
        subkeys.append(subkey)
    return subkeys

def feistel_function(r_block, subkey):
    expanded = apply_permutation(r_block, E)
    xored = [a ^ b for a, b in zip(expanded, subkey)]
    # S盒替换
    s_output = []
    for i in range(8):
        chunk = xored[i*6:(i+1)*6]
        row = (chunk[0] << 1) + chunk[5]
        col = (chunk[1] << 3) + (chunk[2] << 2) + (chunk[3] << 1) + chunk[4]
        s_val = S_BOXES[i][row][col]
        s_output += [int(bit) for bit in f"{s_val:04b}"]
    # P置换
    return apply_permutation(s_output, P)

def des_encrypt(plaintext_bits, key_bits):
    permuted = apply_permutation(plaintext_bits, IP)
    l, r = permuted[:32], permuted[32:]
    # 16个子密钥
    subkeys = generate_subkeys(key_bits)
    # 16轮Feistel
    for i in range(16):
        new_r = [x ^ y for x, y in zip(l, feistel_function(r, subkeys[i]))]
        l, r = r, new_r
    combined = r + l
    ciphertext = apply_permutation(combined, IP_INV)
    return ciphertext
	
def des_decrypt(ciphertext_bits, key_bits):
    """DES解密逆序使用子密钥"""
    permuted = apply_permutation(ciphertext_bits, IP)
    l, r = permuted[:32], permuted[32:]
    subkeys = generate_subkeys(key_bits)[::-1]  # 子密钥逆序
    for i in range(16):
        new_r = [x ^ y for x, y in zip(l, feistel_function(r, subkeys[i]))]
        l, r = r, new_r
    combined = r + l
    plaintext_bits = apply_permutation(combined, IP_INV)
    return plaintext_bits