WMCTF2023部分Reverse

j1ya Lv5
  2023-08-25 16:23:46 2023-08-25 16:23:46 创建   2026-10-02 16:33:49 2026-10-02 16:33:49 更新      

Reverse

ez_android

JNI_Onload函数里动态注册sub_2B90为CheckUsername，sub_32F0为check2

sub_2B90里的sub_57D0函数是RC4魔改，最后多一步异或i

先求出RC4_key

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a=[0x61, 0x1A, 0xA2, 0x79, 0xE6, 0x14, 0x1B, 0x21]
b=[0x50, 0x28, 0x91, 0x4D, 0xD3, 0x22, 0x2C, 0x19]
for i in range(len(a)):
    a[i] ^= b[i]
    print(chr(a[i]), end="")
#12345678

解出账号为Re_1s_eaSy

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def rc4(data, key):
    S = list(range(256))
    j = 0
    out = []

    for i in range(256):
        j = (j + S[i] + key[i % len(key)]) % 256
        S[i], S[j] = S[j], S[i]

    i = 0
    j = 0
    k = 0
    for char in data:
        i = (i + 1) % 256
        j = (j + S[i]) % 256
        S[i], S[j] = S[j], S[i]
        out.append(char ^ S[(S[i] + S[j]) % 256] ^ k)
        k = k + 1
    return bytes(out)

data = bytes([0xe9,0x97,0x64,0xe6,0x7e,0xeb,0xbd,0xc1,0xab,0x43])
key = b'12345678'
decrypted = rc4(data, key)
print(decrypted)

findcrypt插件发现check2是AES算法

v154作为key是Java层拼接的变量Re_1s_eaSy123456，下面是解密调用代码

sub_B30作为AES加密代码，交叉引用byte_9160拿到密文

sub_1080生成轮密钥

sub_1650对应轮密钥加

字节代换

行位移

列混淆

看似标准AES，实则交叉引用发现S盒被魔改了

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class IAES:
    global new_s_box
    def __init__(self):
        self.Nk = 4
        self.Nb = 4
        self.Nr = 10

    def arrays(self, raws):
        Nb = []
        for i in range(4):
            Nb = Nb + [raws[4 * 0 + i], raws[4 * 1 + i], raws[4 * 2 + i], raws[4 * 3 + i]]
        return Nb

    def Inv_arrays(self, raws):
        Inv_raws = []
        for i in range(4):
            Inv_raws = Inv_raws + [raws[4 * 0 + i], raws[4 * 1 + i], raws[4 * 2 + i], raws[4 * 3 + i]]
        return Inv_raws

    def view(self, raws):
        raws = self.Inv_arrays(raws)
        raws = ''.join([x.to_bytes(1, byteorder='big').hex() for x in raws])
        print(raws)

    def view2(self, list):
        for i in range(len(list)):
            print(format(list[i], '2x'), end=' ')
            if i & 3 == 3:  # i%4 == 3
                print('\n', end='')
        print('\n', end='')

    def AddRoundKey(self, raws, Keys):
        AddRoundKey = []
        for raw, Key in zip(raws, Keys):
            AddRoundKey.append(raw ^ Key)
        return AddRoundKey

    def SubBytes(self, raws):
        S_box=new_s_box
        raws_S_box = []
        for raw in raws:
            raws_S_box.append(S_box[raw])
        return raws_S_box

    def InvSubBytes(self, raws,inv_s_box):
        IS_box = inv_s_box
        raws_IS_box = []
        for raw in raws:
            raws_IS_box.append(IS_box[raw])
        return raws_IS_box

    def InvShiftRows(self, raws):
        s13 = raws.pop(7)
        raws.insert(4, s13)
        s2223 = raws[10:12]
        del raws[10:12]
        raws[8:0] = s2223
        s313233 = raws[13:16]
        del raws[13:16]
        raws[12:0] = s313233
        return raws

    def GMUL(self, a, b):  # Russian Peasant Multiplication algorithm
        p = 0
        while a and b:
            if b & 1:  # b%2
                p = p ^ a
            if a & 0x80:  # a=a*x^7(a>0),a >= 2**7(128)
                a = (a << 1) ^ 0x11b  # 0x11b = x^8 + x^4 + x^3 + x + 1 (0b100011011)
            else:
                a = a << 1
            b = b >> 1
        return p

    def InvMixColumns(self, raws):
        for i in range(4):
            raws[0 * 4 + i], \
                raws[1 * 4 + i], \
                raws[2 * 4 + i], \
                raws[3 * 4 + i] \
                = \
                self.GMUL(0x0e, raws[0 * 4 + i]) ^ self.GMUL(0x0b, raws[1 * 4 + i]) ^ self.GMUL(0x0d, raws[
                    2 * 4 + i]) ^ self.GMUL(0x09, raws[3 * 4 + i]), \
                self.GMUL(0x09, raws[0 * 4 + i]) ^ self.GMUL(0x0e, raws[1 * 4 + i]) ^ self.GMUL(0x0b, raws[
                    2 * 4 + i]) ^ self.GMUL(0x0d, raws[3 * 4 + i]), \
                self.GMUL(0x0d, raws[0 * 4 + i]) ^ self.GMUL(0x09, raws[1 * 4 + i]) ^ self.GMUL(0x0e, raws[
                    2 * 4 + i]) ^ self.GMUL(0x0b, raws[3 * 4 + i]), \
                self.GMUL(0x0b, raws[0 * 4 + i]) ^ self.GMUL(0x0d, raws[1 * 4 + i]) ^ self.GMUL(0x09, raws[
                    2 * 4 + i]) ^ self.GMUL(0x0e, raws[3 * 4 + i])
        return raws

    def RotWord(self, temp):
        b0 = temp.pop(0)
        temp.insert(3, b0)
        return temp

    def SubWord(self, temp):
        temp = self.SubBytes(temp)
        return temp

    def KeyExpansion(self, key):
        i = 0
        w = [[0]] * (self.Nb * (self.Nr + 1))
        Rcon = [[0x01, 0x00, 0x00, 0x00],
                [0x02, 0x00, 0x00, 0x00],
                [0x04, 0x00, 0x00, 0x00],
                [0x08, 0x00, 0x00, 0x00],
                [0x10, 0x00, 0x00, 0x00],
                [0x20, 0x00, 0x00, 0x00],
                [0x40, 0x00, 0x00, 0x00],
                [0x80, 0x00, 0x00, 0x00],
                [0x1B, 0x00, 0x00, 0x00],
                [0x36, 0x00, 0x00, 0x00]
                ]
        while i < self.Nk:
            w[i] = ([key[4 * i], key[4 * i + 1], key[4 * i + 2], key[4 * i + 3]])
            i = i + 1

        i = self.Nk

        while i < self.Nb * (self.Nr + 1):
            temp = w[i - 1].copy()
            if i % self.Nk == 0:
                temp = self.SubWord(self.RotWord(temp))
                temp2 = []
                for temp1, Rcon1 in zip(temp, Rcon[(i // self.Nk) - 1]):
                    temp2.append(temp1 ^ Rcon1)
                temp = temp2
            elif self.Nk > 6 and i % self.Nk == 4:
                temp = self.SubWord(temp)
            w_temp = []
            for w1, temp1 in zip(w[i - self.Nk], temp):
                w_temp.append(w1 ^ temp1)
            w[i] = w_temp
            i = i + 1
        return w

    def IAES(self, IInput, Cipher_Key,inv_s_box):
        IInput = [IInput1 for IInput1 in IInput]
        Cipher_Key = [Cipher_Key1 for Cipher_Key1 in Cipher_Key]
        KeyExpansion = self.KeyExpansion(Cipher_Key)
        keys = []
        for Key_index in range(len(KeyExpansion) // 4):
            keys_temp = (KeyExpansion[4 * Key_index] + KeyExpansion[4 * Key_index + 1] + KeyExpansion[
                4 * Key_index + 2] + KeyExpansion[4 * Key_index + 3])
            keys_temp = self.arrays(keys_temp)
            keys.append(keys_temp)
        IInput = self.arrays(IInput)
        self.view(IInput)
        self.view(keys[-1])
        IInput = self.AddRoundKey(IInput, keys[-1])
        self.view(IInput)
        for index in range(self.Nr - 1):
            IInput = self.InvShiftRows(IInput)
            self.view(IInput)
            IInput = self.InvSubBytes(IInput,inv_s_box)
            self.view(IInput)
            self.view(keys[-1 - 1 - index])
            IInput = self.AddRoundKey(IInput, keys[-1 - 1 - index])
            self.view(IInput)
            IInput = self.InvMixColumns(IInput)
            self.view(IInput)
        IInput = self.InvShiftRows(IInput)
        self.view(IInput)
        IInput = self.InvSubBytes(IInput,inv_s_box)
        self.view(IInput)
        self.view(keys[0])
        IInput = self.AddRoundKey(IInput, keys[0])
        self.view(IInput)
        IInput = self.Inv_arrays(IInput)
        IInput = bytes(IInput)
        return IInput


S_box = [
    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
]

new_s_box = [0x29, 0x40, 0x57, 0x6E, 0x85, 0x9C, 0xB3, 0xCA, 0xE1, 0xF8, 
  0x0F, 0x26, 0x3D, 0x54, 0x6B, 0x82, 0x99, 0xB0, 0xC7, 0xDE, 
  0xF5, 0x0C, 0x23, 0x3A, 0x51, 0x68, 0x7F, 0x96, 0xAD, 0xC4, 
  0xDB, 0xF2, 0x09, 0x20, 0x37, 0x4E, 0x65, 0x7C, 0x93, 0xAA, 
  0xC1, 0xD8, 0xEF, 0x06, 0x1D, 0x34, 0x4B, 0x62, 0x79, 0x90, 
  0xA7, 0xBE, 0xD5, 0xEC, 0x03, 0x1A, 0x31, 0x48, 0x5F, 0x76, 
  0x8D, 0xA4, 0xBB, 0xD2, 0xE9, 0x00, 0x17, 0x2E, 0x45, 0x5C, 
  0x73, 0x8A, 0xA1, 0xB8, 0xCF, 0xE6, 0xFD, 0x14, 0x2B, 0x42, 
  0x59, 0x70, 0x87, 0x9E, 0xB5, 0xCC, 0xE3, 0xFA, 0x11, 0x28, 
  0x3F, 0x56, 0x6D, 0x84, 0x9B, 0xB2, 0xC9, 0xE0, 0xF7, 0x0E, 
  0x25, 0x3C, 0x53, 0x6A, 0x81, 0x98, 0xAF, 0xC6, 0xDD, 0xF4, 
  0x0B, 0x22, 0x39, 0x50, 0x67, 0x7E, 0x95, 0xAC, 0xC3, 0xDA, 
  0xF1, 0x08, 0x1F, 0x36, 0x4D, 0x64, 0x7B, 0x92, 0xA9, 0xC0, 
  0xD7, 0xEE, 0x05, 0x1C, 0x33, 0x4A, 0x61, 0x78, 0x8F, 0xA6, 
  0xBD, 0xD4, 0xEB, 0x02, 0x19, 0x30, 0x47, 0x5E, 0x75, 0x8C, 
  0xA3, 0xBA, 0xD1, 0xE8, 0xFF, 0x16, 0x2D, 0x44, 0x5B, 0x72, 
  0x89, 0xA0, 0xB7, 0xCE, 0xE5, 0xFC, 0x13, 0x2A, 0x41, 0x58, 
  0x6F, 0x86, 0x9D, 0xB4, 0xCB, 0xE2, 0xF9, 0x10, 0x27, 0x3E, 
  0x55, 0x6C, 0x83, 0x9A, 0xB1, 0xC8, 0xDF, 0xF6, 0x0D, 0x24, 
  0x3B, 0x52, 0x69, 0x80, 0x97, 0xAE, 0xC5, 0xDC, 0xF3, 0x0A, 
  0x21, 0x38, 0x4F, 0x66, 0x7D, 0x94, 0xAB, 0xC2, 0xD9, 0xF0, 
  0x07, 0x1E, 0x35, 0x4C, 0x63, 0x7A, 0x91, 0xA8, 0xBF, 0xD6, 
  0xED, 0x04, 0x1B, 0x32, 0x49, 0x60, 0x77, 0x8E, 0xA5, 0xBC, 
  0xD3, 0xEA, 0x01, 0x18, 0x2F, 0x46, 0x5D, 0x74, 0x8B, 0xA2, 
  0xB9, 0xD0, 0xE7, 0xFE, 0x15, 0x2C, 0x43, 0x5A, 0x71, 0x88, 
  0x9F, 0xB6, 0xCD, 0xE4, 0xFB, 0x12]

new_contrary_sbox = [0] * 256

for i in range(256):
    line = (new_s_box[i] & 0xf0) >> 4

    rol = new_s_box[i] & 0xf

    new_contrary_sbox[(line * 16) + rol] = i

print(new_contrary_sbox)
IInput = bytes.fromhex('2bc8208b5c0da79b2a513ad27171ca50')
print(IInput)
Cipher_Key = bytes(b'Re_1s_eaSy123456')
print(Cipher_Key)
Out = IAES().IAES(IInput, Cipher_Key,new_contrary_sbox)
print(Out)
# _eZ_Rc4_@nd_AES!

最后拼接得到flag：WMCTF{Re_1s_eaSy_eZ_Rc4_@nd_AES!}

  • 标题: WMCTF2023部分Reverse
  • 作者: j1ya
  • 创建于 : 2023-08-25 16:23:46
  • 更新于 : 2026-10-02 16:33:49
  • 链接: https://j1ya-22.github.io/2023/08/25/WMCTF2023部分Reverse/
  • 版权声明: 本文章采用 CC BY-NC-SA 4.0 进行许可。
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目录
WMCTF2023部分Reverse
  1. Reverse
    1. ez_android