昨天抓住放假的尾巴做了道题

2019 CISCN part_des
题目描述：

Round n part_encode-> 0x92d915250119e12b
Key map -> 0xe0be661032d5f0b676f82095e4d67623628fe6d376363183aed373a60167af537b46abc2af53d97485591f5bd94b944a3f49d94897ea1f699d1cdc291f2d9d4a5c705f2cad89e938dbacaca15e10d8aeaed90236f0be2e954a8cf0bea6112e84

是加密了n轮的密码
key变成二进制后长度是768，刚好是48的16倍，那么就是一个DES了

解密：

from Crypto.Util.number import long_to_bytes
IP = [
        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
        ]
IP_re = [
        40,8,48,16,56,24,64,32,39,7,47,15,55,23,63,31,
        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
    ]
Pbox = [
        16,7,20,21,29,12,28,17,1,15,23,26,5,18,31,10,
        2,8,24,14,32,27,3,9,19,13,30,6,22,11,4,25
]
E = [
        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
    ]      
PC1 = [
        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
    ]
PC2 = [
        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
    ]
Sbox = [
    [
        [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],
    ]
]

part_decode='1001001011011001000101010010010100000001000110011110000100101011'
Key=['111000001011111001100110000100000011001011010101', '111100001011011001110110111110000010000010010101', '111001001101011001110110001000110110001010001111', '111001101101001101110110001101100011000110000011', '101011101101001101110011101001100000000101100111', '101011110101001101111011010001101010101111000010', '101011110101001111011001011101001000010101011001', '000111110101101111011001010010111001010001001010', '001111110100100111011001010010001001011111101010', '000111110110100110011101000111001101110000101001', '000111110010110110011101010010100101110001110000', '010111110010110010101101100010011110100100111000', '110110111010110010101100101000010101111000010000', '110110001010111010101110110110010000001000110110', '111100001011111000101110100101010100101010001100', '111100001011111010100110000100010010111010000100']
rounds=16
def DES(L,R,key):
    R0=L
    EPre=''
    XORre=''
    Sre=''
    Pre=''

    for i in range(len(E)):
        EPre+=R0[E[i]-1]
        
    EPre=bin(int(EPre,2))
    key=bin(int(key,2))
    XORre=str(bin(eval(EPre)^eval(key)))
    XORre=XORre[2:].zfill(48)
    

    #S盒置换：
    for j in range(8):
        column=''
        row=''
        s=XORre[6*j:6*(j+1)]
        row=int(s[0]+s[-1],2)
        column=int(s[1:-1],2)
        re=str(bin(Sbox[j][row][column]))
        Sre+=re[2:].zfill(4)

    #P盒置换
    for k in range(len(Pbox)):
        Pre+=Sre[Pbox[k]-1]

    Pre=bin(int(Pre,2))
    R=bin(int(R,2))
    L0=str(bin(eval(Pre)^eval(R)))
    L0=L0[2:].zfill(32)
    R0=L
    return L0,R0

while rounds>=0:
    L=part_decode[:32]
    R=part_decode[32:]
    oriplain=''

    for i in range(rounds):
        key=Key[rounds-i-1]
        L,R=DES(L,R,key)
    subplain=L+R
    for i in range(len(IP_re)):
        oriplain+=subplain[IP_re[i]-1]
    print(rounds,long_to_bytes(int(oriplain,2)))
    rounds-=1
    

跑出来是这个样子的：

16 b'\x84\x1e\x8a\x17^#Q\x83'  
15 b'\x8a\x1eD\x9a0\x94\x18/'  
14 b't-\xcfE\xcfx\x90\xa7'     
13 b'y0ur9Ood'
12 b'\xb5p^\xdb\xe9=\xb9\x88'  
11 b')\xc1`r\xfb\xd5\xfb\x9d'  
10 b'\xc2o\xe3\xaah\x0e\xe1f'  
9 b'\x93\xc0\xa4Zz\xa2\xbb\x13'
8 b'\xf2\x1b ;\xf0\xdc\xa4\xdf'
7 b'\xd7\xcd\x0e9\xd2\x185S'   
6 b'Bh\xa4~$)\x1e\xa3'
5 b'5\xa3!P\n\xf4\xcb\xe2'     
4 b'&L\x1b\x9c\x85tT\xae'
3 b'l\xc7!\x97\x08@\x1c\xe9'
2 b'l\xa71?I}3{'
1 b'/\xd4\x0f5\xe8B!\xb1'
0 b'\xbfB\x052t\x0b\x18X'

得到flag{y0ur9Ood}

其实只要知道DES的原理就很简单了