2025n1CTF Re-wp+复现

5mc

virtureprotect动态修改函数，用ida动态调试，给输入的数据下硬件断点运行分析就可以发现正确的逻辑。

但是不能反汇编，选中按c恢复成汇编代码。

直接读汇编写出加密代码，注意一下细节，每次循环左移的值都是不一样的，以防万一还是每次加密都细看了一下。一共有四种加密方法，四种加密循环进行一共十六次加密，顺序大概是box()–>index()–>shift(stat==0)–>shift(stat==1)–>……。直接写出逆向函数就行，密文就在比对的位置。

#include <stdio.h>
#include <stdint.h>

//加密函数
int box(unsigned char* data) {
    unsigned char sbox[] = { 0xB0, 0xF0, 0x21, 0xCF, 0xF2, 0x04, 0x3A, 0x68, 0x84, 0x7B, 0x39, 0x86, 0x36, 0x87, 0x9B, 0xF7,
    0x3D, 0x18, 0x1E, 0x61, 0x1B, 0x2E, 0x6C, 0xDF, 0x2C, 0xAE, 0x65, 0x9D, 0xEB, 0x2F, 0xDA, 0xF4,
    0xDE, 0xCA, 0x56, 0x92, 0x75, 0x3B, 0x62, 0x45, 0x06, 0x3C, 0x52, 0x33, 0x6E, 0x25, 0xCE, 0xA3,
    0xD2, 0x44, 0xA1, 0x4A, 0x58, 0xB1, 0xA0, 0x2A, 0x47, 0x0A, 0x02, 0xAF, 0x50, 0xC3, 0xDC, 0xEA,
    0xE5, 0x0D, 0x67, 0x91, 0xE1, 0x51, 0xE3, 0xC1, 0xAA, 0x95, 0x5C, 0x79, 0x72, 0x1C, 0x3F, 0xB8,
    0xE8, 0x1F, 0xFF, 0x7A, 0x73, 0x26, 0x54, 0x9E, 0xED, 0xA9, 0x41, 0x20, 0xEF, 0xA6, 0x48, 0x97,
    0x4F, 0xD4, 0xBB, 0x23, 0x66, 0xD9, 0xE4, 0x0B, 0x30, 0x15, 0xD7, 0x6B, 0x19, 0xCD, 0xC4, 0x08,
    0xB4, 0xC8, 0x14, 0xFD, 0x7F, 0x28, 0x0E, 0x05, 0x0F, 0x4B, 0x6F, 0xF5, 0x90, 0x76, 0xBF, 0x60,
    0xE7, 0x24, 0x78, 0x6D, 0x71, 0xA8, 0x43, 0xB5, 0x0C, 0x31, 0xF9, 0xA2, 0x9C, 0x99, 0xF6, 0x2D,
    0xDB, 0xB7, 0xC9, 0x85, 0x81, 0x03, 0x64, 0x1D, 0x07, 0x34, 0x5A, 0xBD, 0x37, 0x4C, 0xA7, 0x5F,
    0x46, 0xE9, 0x35, 0x93, 0x8D, 0xA5, 0xFB, 0x42, 0x01, 0xC2, 0x17, 0x12, 0x1A, 0x77, 0xC6, 0x53,
    0x83, 0x4D, 0xB2, 0x10, 0x2B, 0xF8, 0x88, 0x6A, 0x3E, 0xD0, 0x7C, 0x63, 0x40, 0x27, 0xBE, 0xD5,
    0x38, 0xD1, 0x74, 0xB6, 0x57, 0x94, 0xAB, 0x8A, 0xB9, 0xBC, 0x7D, 0xB3, 0x96, 0x7E, 0xFC, 0xAD,
    0x22, 0x4E, 0xFA, 0xE0, 0xCB, 0x8B, 0xEE, 0x32, 0xA4, 0x16, 0xFE, 0x5B, 0x13, 0xDD, 0xC0, 0x9A,
    0x5E, 0x8E, 0x29, 0xF3, 0x8F, 0x49, 0xE6, 0x9F, 0xF1, 0xC5, 0x70, 0x55, 0x8C, 0x11, 0xCC, 0x5D,
    0xEC, 0x00, 0xAC, 0x89, 0xD3, 0x82, 0x69, 0xD6, 0xBA, 0xD8, 0x59, 0x98, 0x09, 0x80, 0xE2, 0xC7
    };
    
    for (int i = 0; i < 32;i++) {
        data[i] = sbox[data[i]];
    }
    return 0;
}
int index(unsigned char* data) {
    unsigned char tmp[32], table[32] = { 0x13, 0x1F, 0x10, 0x1D, 0x01, 0x0D, 0x07, 0x15, 0x08, 0x06, 0x16, 0x00, 0x0F, 0x0C, 0x02, 0x05, 0x0E,0x03, 0x12, 0x04, 0x18, 0x14, 0x1A, 0x1C, 0x1E, 0x19, 0x09, 0x1B, 0x11, 0x0B, 0x17, 0x0A };
    for (int i = 0; i < 32; i++) {
        tmp[table[i]] = data[i];
    }
    for (int i = 0; i < 32; i++) {
        data[table[i]] = tmp[i];
    }
    
    return 0;
}

int shift(int l, int r, unsigned char* data,int stat) {
    unsigned char indext2[] = { 0x7D, 0xB7, 0x24, 0x7E, 0xC3, 0x6B, 0xBD, 0xD8, 0x7F, 0x13, 0x6E, 0x0F, 0x43, 0xCD, 0x6B, 0xCF, 0x18,
               0x4F, 0x26, 0x18, 0x12, 0x2A, 0x7E, 0x9B, 0x27, 0x4C, 0x33, 0x67, 0x40, 0xC9, 0x9E, 0xC4 },
        indextb2[] = { 0x91, 0xDB, 0x9F, 0x5F, 0x26, 0x27, 0xD6, 0xA8, 0xBF, 0x41, 0x16, 0x79, 0xDE, 0x73, 0x16, 0xF8, 0x1E,
                0xBA, 0x6A, 0xBE, 0xC6, 0x12, 0xB2, 0x39, 0x9E, 0xF3, 0x12, 0x4E, 0x02, 0x1C, 0xE2, 0x43 };
    if (stat == 0) {
        for (int i = 0; i < 32; i++) {
            unsigned char c;
            c = data[i] ^ indext2[i];
            data[i] = c + indextb2[i];
            data[i] = (data[i] << l) | (data[i] >> r);
        }
    }
    else {
        for (int i = 0; i < 32; i++) {
            data[i] = (data[i] + indextb2[i]) ^ indext2[i];
            data[i] = (data[i] << l) | (data[i] >> r);
        }
    }
    
    return 0;
}
//解密函数

int rebox(unsigned char* data) {
    unsigned char sbox[] = { 0xB0, 0xF0, 0x21, 0xCF, 0xF2, 0x04, 0x3A, 0x68, 0x84, 0x7B, 0x39, 0x86, 0x36, 0x87, 0x9B, 0xF7,
    0x3D, 0x18, 0x1E, 0x61, 0x1B, 0x2E, 0x6C, 0xDF, 0x2C, 0xAE, 0x65, 0x9D, 0xEB, 0x2F, 0xDA, 0xF4,
    0xDE, 0xCA, 0x56, 0x92, 0x75, 0x3B, 0x62, 0x45, 0x06, 0x3C, 0x52, 0x33, 0x6E, 0x25, 0xCE, 0xA3,
    0xD2, 0x44, 0xA1, 0x4A, 0x58, 0xB1, 0xA0, 0x2A, 0x47, 0x0A, 0x02, 0xAF, 0x50, 0xC3, 0xDC, 0xEA,
    0xE5, 0x0D, 0x67, 0x91, 0xE1, 0x51, 0xE3, 0xC1, 0xAA, 0x95, 0x5C, 0x79, 0x72, 0x1C, 0x3F, 0xB8,
    0xE8, 0x1F, 0xFF, 0x7A, 0x73, 0x26, 0x54, 0x9E, 0xED, 0xA9, 0x41, 0x20, 0xEF, 0xA6, 0x48, 0x97,
    0x4F, 0xD4, 0xBB, 0x23, 0x66, 0xD9, 0xE4, 0x0B, 0x30, 0x15, 0xD7, 0x6B, 0x19, 0xCD, 0xC4, 0x08,
    0xB4, 0xC8, 0x14, 0xFD, 0x7F, 0x28, 0x0E, 0x05, 0x0F, 0x4B, 0x6F, 0xF5, 0x90, 0x76, 0xBF, 0x60,
    0xE7, 0x24, 0x78, 0x6D, 0x71, 0xA8, 0x43, 0xB5, 0x0C, 0x31, 0xF9, 0xA2, 0x9C, 0x99, 0xF6, 0x2D,
    0xDB, 0xB7, 0xC9, 0x85, 0x81, 0x03, 0x64, 0x1D, 0x07, 0x34, 0x5A, 0xBD, 0x37, 0x4C, 0xA7, 0x5F,
    0x46, 0xE9, 0x35, 0x93, 0x8D, 0xA5, 0xFB, 0x42, 0x01, 0xC2, 0x17, 0x12, 0x1A, 0x77, 0xC6, 0x53,
    0x83, 0x4D, 0xB2, 0x10, 0x2B, 0xF8, 0x88, 0x6A, 0x3E, 0xD0, 0x7C, 0x63, 0x40, 0x27, 0xBE, 0xD5,
    0x38, 0xD1, 0x74, 0xB6, 0x57, 0x94, 0xAB, 0x8A, 0xB9, 0xBC, 0x7D, 0xB3, 0x96, 0x7E, 0xFC, 0xAD,
    0x22, 0x4E, 0xFA, 0xE0, 0xCB, 0x8B, 0xEE, 0x32, 0xA4, 0x16, 0xFE, 0x5B, 0x13, 0xDD, 0xC0, 0x9A,
    0x5E, 0x8E, 0x29, 0xF3, 0x8F, 0x49, 0xE6, 0x9F, 0xF1, 0xC5, 0x70, 0x55, 0x8C, 0x11, 0xCC, 0x5D,
    0xEC, 0x00, 0xAC, 0x89, 0xD3, 0x82, 0x69, 0xD6, 0xBA, 0xD8, 0x59, 0x98, 0x09, 0x80, 0xE2, 0xC7
    };
    for (int i = 0; i < 32;i++) {
        for (int j = 0; j < 256;j++) {
            if (data[i] == sbox[j]) {
                data[i] = j;
                break;
            }
            
        }
    }
    return 0;
}

int reindex(unsigned char *data) {
    unsigned char tmp[32], table[32] = { 0x13, 0x1F, 0x10, 0x1D, 0x01, 0x0D, 0x07, 0x15, 0x08, 0x06, 0x16, 0x00, 0x0F, 0x0C, 0x02, 0x05, 0x0E,0x03, 0x12, 0x04, 0x18, 0x14, 0x1A, 0x1C, 0x1E, 0x19, 0x09, 0x1B, 0x11, 0x0B, 0x17, 0x0A };
    for (int i = 0; i < 32; i++) {
        tmp[i] = data[table[i]];
    }
    for (int i = 0; i < 32; i++) {
        data[i] = tmp[table[i]];
    }
    return 0;
}

int reshift(int l, int r, unsigned char* data,int stat) {
    unsigned char indext2[] = { 0x7D, 0xB7, 0x24, 0x7E, 0xC3, 0x6B, 0xBD, 0xD8, 0x7F, 0x13, 0x6E, 0x0F, 0x43, 0xCD, 0x6B, 0xCF, 0x18,
               0x4F, 0x26, 0x18, 0x12, 0x2A, 0x7E, 0x9B, 0x27, 0x4C, 0x33, 0x67, 0x40, 0xC9, 0x9E, 0xC4 },
        indextb2[] = { 0x91, 0xDB, 0x9F, 0x5F, 0x26, 0x27, 0xD6, 0xA8, 0xBF, 0x41, 0x16, 0x79, 0xDE, 0x73, 0x16, 0xF8, 0x1E,
                0xBA, 0x6A, 0xBE, 0xC6, 0x12, 0xB2, 0x39, 0x9E, 0xF3, 0x12, 0x4E, 0x02, 0x1C, 0xE2, 0x43 };
    if (stat == 1) {
        for (int i = 0; i < 32; i++) {
            unsigned char c;
            data[i] = (data[i] >> l) | (data[i] << r);
            c = data[i] - indextb2[i];
            data[i] = c ^ indext2[i];
        }
    }
    else {
        for (int i = 0; i < 32; i++) {
            unsigned char c;
            data[i] = (data[i] >> l) | (data[i] << r);
            data[i] = (data[i] ^ indext2[i]) - indextb2[i];
        }
    }
    
    return 0;
}

void prlhex(unsigned char* data,const char *hit) {
    printf("\n--------------------------------------------------------------------------------------\n");
    printf("--------%s\n", hit);
    for (int i = 0; i < 32; i++) {
        printf("%02x ", data[i]);
    }
}

int main() {
    unsigned char data[] = { 0x5B, 0x2D, 0xE9, 0x66, 0xED, 0x39, 0x90, 0x23, 0xAF, 0xDA, 0xEB, 0x2E, 0xD1, 0x0D, 0xBB, 0xBD, 0x57, 0x52, 0x02, 0xB0, 0xBA, 0x9D, 0x52, 0xFA, 0x67, 0xEE, 0xA3, 0x85, 0xA9, 0x84, 0xE2, 0x6F };
    reshift(1, 7, data,0);  //逆向解密
    reshift(2, 6, data,1);
    reindex(data);
    rebox(data);
    reshift(5, 3, data,0);
    reshift(3, 5, data,1);
    reindex(data);
    rebox(data);
    reshift(4, 4, data,0);
    reshift(6, 2, data,1);
    reindex(data);
    rebox(data);
    reshift(7, 1, data,0);
    reshift(3, 5, data,1);
    reindex(data);
    rebox(data);
    for (int i = 0; i < 32; i++) {
        printf("%c", data[i]);
    }
    return 0;
}
//flag{Master_of_5mc_XoR_aDD_r0r!}

---

sf5

有四个加密函数被存储在了数组v28里，并以每次加密次数为索引获取加密前的数据然后进行按位或操作(Buf1[v3++] & 3)，以这个结果为索引加载数组v28中的函数进行加密。先分析四个加密函数，

v28[0]是一个盒的查找替换，v28[1]以一个索引表对数据进行打乱，v28[2]把输入与两串常量异或并相加，v28[3]把数据每一字节循环右移了3位。值得注意的是这里的v28[2]是有点难看懂的，要结合汇编动调才能完全理解，下面是一些理解。

加密逻辑大概如下

//encode
#include <stdio.h>
#include <string.h>
#include <stdint.h>

int enc1(uint8_t* data) {
    uint8_t sbox[256] = { 0xB0, 0xF0, 0x21, 0xCF, 0xF2, 0x04, 0x3A, 0x68, 0x84, 0x7B, 0x39, 0x86, 0x36, 0x87, 0x9B, 0xF7, 0x3D, 0x18,
            0x1E, 0x61, 0x1B, 0x2E, 0x6C, 0xDF, 0x2C, 0xAE, 0x65, 0x9D, 0xEB, 0x2F, 0xDA, 0xF4, 0xDE, 0xCA, 0x56, 0x92,
            0x75, 0x3B, 0x62, 0x45, 0x06, 0x3C, 0x52, 0x33, 0x6E, 0x25, 0xCE, 0xA3, 0xD2, 0x44, 0xA1, 0x4A, 0x58, 0xB1,
            0xA0, 0x2A, 0x47, 0x0A, 0x02, 0xAF, 0x50, 0xC3, 0xDC, 0xEA, 0xE5, 0x0D, 0x67, 0x91, 0xE1, 0x51, 0xE3, 0xC1,
            0xAA, 0x95, 0x5C, 0x79, 0x72, 0x1C, 0x3F, 0xB8, 0xE8, 0x1F, 0xFF, 0x7A, 0x73, 0x26, 0x54, 0x9E, 0xED, 0xA9,
            0x41, 0x20, 0xEF, 0xA6, 0x48, 0x97, 0x4F, 0xD4, 0xBB, 0x23, 0x66, 0xD9, 0xE4, 0x0B, 0x30, 0x15, 0xD7, 0x6B,
            0x19, 0xCD, 0xC4, 0x08, 0xB4, 0xC8, 0x14, 0xFD, 0x7F, 0x28, 0x0E, 0x05, 0x0F, 0x4B, 0x6F, 0xF5, 0x90, 0x76,
            0xBF, 0x60, 0xE7, 0x24, 0x78, 0x6D, 0x71, 0xA8, 0x43, 0xB5, 0x0C, 0x31, 0xF9, 0xA2, 0x9C, 0x99, 0xF6, 0x2D,
            0xDB, 0xB7, 0xC9, 0x85, 0x81, 0x03, 0x64, 0x1D, 0x07, 0x34, 0x5A, 0xBD, 0x37, 0x4C, 0xA7, 0x5F, 0x46, 0xE9,
            0x35, 0x93, 0x8D, 0xA5, 0xFB, 0x42, 0x01, 0xC2, 0x17, 0x12, 0x1A, 0x77, 0xC6, 0x53, 0x83, 0x4D, 0xB2, 0x10,
            0x2B, 0xF8, 0x88, 0x6A, 0x3E, 0xD0, 0x7C, 0x63, 0x40, 0x27, 0xBE, 0xD5, 0x38, 0xD1, 0x74, 0xB6, 0x57, 0x94,
            0xAB, 0x8A, 0xB9, 0xBC, 0x7D, 0xB3, 0x96, 0x7E, 0xFC, 0xAD, 0x22, 0x4E, 0xFA, 0xE0, 0xCB, 0x8B, 0xEE, 0x32,
            0xA4, 0x16, 0xFE, 0x5B, 0x13, 0xDD, 0xC0, 0x9A, 0x5E, 0x8E, 0x29, 0xF3, 0x8F, 0x49, 0xE6, 0x9F, 0xF1, 0xC5,
            0x70, 0x55, 0x8C, 0x11, 0xCC, 0x5D, 0xEC, 0x00, 0xAC, 0x89, 0xD3, 0x82, 0x69, 0xD6, 0xBA, 0xD8, 0x59, 0x98,
            0x09, 0x80, 0xE2, 0xC7 };
    for (int i = 0; i < 32; i++) {
        data[i] = sbox[data[i]];
    }
    return 0;
}

int enc2(uint8_t* data) {
    unsigned char tmp[32], table[32] = { 0x13, 0x1F, 0x10, 0x1D, 0x01, 0x0D, 0x07, 0x15, 0x08, 0x06, 0x16, 0x00, 0x0F, 0x0C, 0x02, 0x05, 0x0E,0x03, 0x12, 0x04, 0x18, 0x14, 0x1A, 0x1C, 0x1E, 0x19, 0x09, 0x1B, 0x11, 0x0B, 0x17, 0x0A };
    for (int i = 0; i < 32; i++) {
        tmp[table[i]] = data[i];
    }
    for (int i = 0; i < 32; i++) {
       data[table[i]] = tmp[i];
    }
    return 0;
}

int enc3(uint8_t* data) {
    uint8_t index1[] = { 0x7D, 0xB7, 0x24, 0x7E, 0xC3, 0x6B, 0xBD, 0xD8, 0x7F, 0x13, 0x6E, 0x0F, 0x43, 0xCD, 0x6B, 0xCF,
    0x18, 0x4F, 0x26, 0x18, 0x12, 0x2A, 0x7E, 0x9B, 0x27, 0x4C, 0x33, 0x67, 0x40, 0xC9, 0x9E, 0xC4 };
    uint8_t index2[] = { 0x91, 0xDB, 0x9F, 0x5F, 0x26, 0x27, 0xD6, 0xA8, 0xBF, 0x41, 0x16, 0x79, 0xDE, 0x73, 0x16, 0xF8,
    0x1E, 0xBA, 0x6A, 0xBE, 0xC6, 0x12, 0xB2, 0x39, 0x9E, 0xF3, 0x12, 0x4E, 0x02, 0x1C, 0xE2, 0x43 };
    for (int i = 0; i < 32; i++) {
        data[i] ^= index1[i];
        data[i] += index2[i];

    }
    return 0;

}
int enc4(uint8_t* data) {
    for (int i = 0; i < 32; i++) {
        data[i] = (data[i] >> 3) | (data[i] << 5);
    }
    return 0；
}

因为不知道明文，我们每一次的解密有4种可能性，题目也提示dfs，我们就用dfs遍历解密路径就行。我们可以检查在解密后31减去解密次数与3进行与操作(data[31-step] & 3)是不是当前解密函数的下标，以确定路径，减少遍历的时间。结尾检查flag输出即可。

写出解密函数和dfs，脚本如下。

//decode
#include <stdio.h>
#include <stdint.h>
#include <string.h>

void prlhex(uint8_t* data, const char* hit);

int refun4(uint8_t* data) {
    for (int i = 0; i < 32; i++) {
        data[i] = (data[i] << 3) | (data[i] >> 5);
    }
    return 0;
}

int refun2(uint8_t *data) {
    unsigned char tmp[32], table[32] = { 0x13, 0x1F, 0x10, 0x1D, 0x01, 0x0D, 0x07, 0x15, 0x08, 0x06, 0x16, 0x00, 0x0F, 0x0C, 0x02, 0x05, 0x0E,0x03, 0x12, 0x04, 0x18, 0x14, 0x1A, 0x1C, 0x1E, 0x19, 0x09, 0x1B, 0x11, 0x0B, 0x17, 0x0A };
    for (int i = 0; i < 32; i++) {
        tmp[i] = data[table[i]];
    }
    for (int i = 0; i < 32; i++) {
        data[i] = tmp[table[i]];
    }
    
    return 0;
}

int refun3(uint8_t* data) {
    uint8_t index1[] = { 0x7D, 0xB7, 0x24, 0x7E, 0xC3, 0x6B, 0xBD, 0xD8, 0x7F, 0x13, 0x6E, 0x0F, 0x43, 0xCD, 0x6B, 0xCF,
    0x18, 0x4F, 0x26, 0x18, 0x12, 0x2A, 0x7E, 0x9B, 0x27, 0x4C, 0x33, 0x67, 0x40, 0xC9, 0x9E, 0xC4 };
    uint8_t index2[] = { 0x91, 0xDB, 0x9F, 0x5F, 0x26, 0x27, 0xD6, 0xA8, 0xBF, 0x41, 0x16, 0x79, 0xDE, 0x73, 0x16, 0xF8,
    0x1E, 0xBA, 0x6A, 0xBE, 0xC6, 0x12, 0xB2, 0x39, 0x9E, 0xF3, 0x12, 0x4E, 0x02, 0x1C, 0xE2, 0x43 };
    for (int i = 0; i < 32; i++) {

        data[i] = (data[i] - index2[i]) ^ index1[i];

    }
    return 0;
}

int refun1(uint8_t* data) {
    uint8_t sbox[256] = { 0xB0, 0xF0, 0x21, 0xCF, 0xF2, 0x04, 0x3A, 0x68, 0x84, 0x7B, 0x39, 0x86, 0x36, 0x87, 0x9B, 0xF7, 0x3D, 0x18,
            0x1E, 0x61, 0x1B, 0x2E, 0x6C, 0xDF, 0x2C, 0xAE, 0x65, 0x9D, 0xEB, 0x2F, 0xDA, 0xF4, 0xDE, 0xCA, 0x56, 0x92,
            0x75, 0x3B, 0x62, 0x45, 0x06, 0x3C, 0x52, 0x33, 0x6E, 0x25, 0xCE, 0xA3, 0xD2, 0x44, 0xA1, 0x4A, 0x58, 0xB1,
            0xA0, 0x2A, 0x47, 0x0A, 0x02, 0xAF, 0x50, 0xC3, 0xDC, 0xEA, 0xE5, 0x0D, 0x67, 0x91, 0xE1, 0x51, 0xE3, 0xC1,
            0xAA, 0x95, 0x5C, 0x79, 0x72, 0x1C, 0x3F, 0xB8, 0xE8, 0x1F, 0xFF, 0x7A, 0x73, 0x26, 0x54, 0x9E, 0xED, 0xA9,
            0x41, 0x20, 0xEF, 0xA6, 0x48, 0x97, 0x4F, 0xD4, 0xBB, 0x23, 0x66, 0xD9, 0xE4, 0x0B, 0x30, 0x15, 0xD7, 0x6B,
            0x19, 0xCD, 0xC4, 0x08, 0xB4, 0xC8, 0x14, 0xFD, 0x7F, 0x28, 0x0E, 0x05, 0x0F, 0x4B, 0x6F, 0xF5, 0x90, 0x76,
            0xBF, 0x60, 0xE7, 0x24, 0x78, 0x6D, 0x71, 0xA8, 0x43, 0xB5, 0x0C, 0x31, 0xF9, 0xA2, 0x9C, 0x99, 0xF6, 0x2D,
            0xDB, 0xB7, 0xC9, 0x85, 0x81, 0x03, 0x64, 0x1D, 0x07, 0x34, 0x5A, 0xBD, 0x37, 0x4C, 0xA7, 0x5F, 0x46, 0xE9,
            0x35, 0x93, 0x8D, 0xA5, 0xFB, 0x42, 0x01, 0xC2, 0x17, 0x12, 0x1A, 0x77, 0xC6, 0x53, 0x83, 0x4D, 0xB2, 0x10,
            0x2B, 0xF8, 0x88, 0x6A, 0x3E, 0xD0, 0x7C, 0x63, 0x40, 0x27, 0xBE, 0xD5, 0x38, 0xD1, 0x74, 0xB6, 0x57, 0x94,
            0xAB, 0x8A, 0xB9, 0xBC, 0x7D, 0xB3, 0x96, 0x7E, 0xFC, 0xAD, 0x22, 0x4E, 0xFA, 0xE0, 0xCB, 0x8B, 0xEE, 0x32,
            0xA4, 0x16, 0xFE, 0x5B, 0x13, 0xDD, 0xC0, 0x9A, 0x5E, 0x8E, 0x29, 0xF3, 0x8F, 0x49, 0xE6, 0x9F, 0xF1, 0xC5,
            0x70, 0x55, 0x8C, 0x11, 0xCC, 0x5D, 0xEC, 0x00, 0xAC, 0x89, 0xD3, 0x82, 0x69, 0xD6, 0xBA, 0xD8, 0x59, 0x98,
            0x09, 0x80, 0xE2, 0xC7 };
    for (int i = 0; i < 32;i++) {
        for (int j = 0; j < 256;j++) {
            if (data[i] == sbox[j]) {
                data[i] = j;
                break;
            }
            
        }
    }
    return 0;
}

int backupdata(uint8_t *data,uint8_t *data2) {
    for (int i = 0; i < 32; i++) {
        data[i] = data2[i];
    }
    return 0;
}

int (*refun[4])(uint8_t*) = { refun1, refun2, refun3, refun4 }; 

int check(unsigned char* data) {
    if (!strncmp((char*)data, "flag", 4)) {
        prlhex(data, "result");  //flag
    }
    return 0;
}

int dfs(uint8_t* data, int step, int* path) {
    if (step == 32) {  
        check(data); //检查结果
        return 1;
    }

    uint8_t backup[256];
    backupdata(backup, data);  //备份密文

    for (int i = 0; i < 4; i++) {  //四个解密函数进行解密
        refun[i](data);
        if ((data[31-step] & 3) == i) {  //用&3剪枝
            path[step] = i;
            dfs(data, step + 1, path);
        }
        backupdata(data,backup);
    }

    return 0;
}

void prlhex(uint8_t* data,const char *hit) {
    printf("\n------------------------------------------------------------------------------\n");
    printf("--------%s\n", hit);
    for (int i = 0; i < 32; i++) {
        printf("%c", data[i]);
    }
}

int main() {
    
    uint8_t ciphertext[] = { 0x65, 0x3E, 0x43, 0xB8, 0xBA, 0xDB, 0xF6, 0x88, 0x25, 0x1B, 0x28, 0xC7, 0xC0, 0x54, 0xA6, 0x4A,
    0x90, 0x37, 0xBC, 0x29, 0x41, 0xAA, 0x28, 0xDB, 0x9A, 0x59, 0x63, 0x9E, 0x4B, 0xCF, 0x2E, 0x41 };
    int path[32];

    dfs(ciphertext, 0, path);

    return 0;
}
//flag{Ea5y_enCrypt_And_decrYpt!!}

easy-re

拿下来是一个Android elf文件，用真机运行几次发现报错先分析代码。

看了一下main函数才知道要带参数运行。加了许多混淆，c代码难以阅读，不过还是看到了一些rc4加密。字符串也被加密了，写个脚本用于dnmp。

var inter =setInterval(function() { dump(); }, 3);
function dump() {

var libxx = Process.getModuleByName("easy-re");
var exe_s_size=0x0
console.log("*****************************************************");
console.log("name: " +libxx.name);
console.log("base: " +libxx.base);
console.log("size: " +ptr(libxx.size));
var file_path =  libxx.name + "_" + libxx.base + "_" + ptr(libxx.size) + ".so";
console.log(file_path);
var file_handle = new File(file_path, "wb");
if (file_handle && file_handle != null) {
    Memory.protect(ptr(libxx.base), libxx.size, 'rwx');

    var buffer = ptr(libxx.base).add(exe_s_size).readByteArray(libxx.size-exe_s_size);
    file_handle.write(buffer);
    file_handle.flush();
    file_handle.close();
    console.log("[dump]:", file_path);
}
clearInterval(inter)
}

再用Sofixer修复一下偏移。

重新在ida中分析，在Init_array有一个ptrace检测,可以通过字符串看出来。如果程序执行被检测到ptrace就会出现异常的结果。

c代码太难看了，尝试动调，发现ida调试是可以用的（ptrace检测没有直接结束程序），我们可以用Ida调试elf并利用trace来分析程序算法。Trace结果过长就不展示了。

大概逻辑就是flag_char ^ index ^一个表 ^ 异或前一个char，那个表估计是rc4的。主要的难点是这个表，当前调试是被ptrace检测的，测试过多次，直接使用常规frida调试也是被检测了的。

由于ptrace检测，不是很好patch，打算用环境变量加载frida_gadget来启动frida，PRE_LOAD=/data/local/tmp/frida-gadget.so ./easy-re AAAAAABAAAAAAAAAAAAAAAAAAAAAAAAB

hook脚本

function time(num)
{
let sum=0
for(let i=0;i<num*1024;i++){
sum+=i;
}
}
var mInterval = setInterval(function () {
    var sgame = Process.findModuleByName("easy-re");
    if (sgame == null) {
        console.log("无");
        return;
    }
    clearInterval(mInterval);
    //  var addr = sgame.base.add(0x1400012A0-0x140000000) //windows
    var addr = sgame.base.add(0x05BC0309280 - 0x005BC0307000)
    console.log("" + addr);
    console.log(Instruction.parse(addr).toString());
    Interceptor.attach(addr, {
        onEnter: function (args) {
            var rax = this.context.x10;
            console.log( rax,",");
            time(5451)
        }
    })

    addr = sgame.base.add(0x5BC03094F0 - 0x005BC0307000)
    console.log("" + addr);
    console.log(Instruction.parse(addr).toString());
    Interceptor.attach(addr, {
        onEnter: function (args) {
            var rax = this.context.x1;
            // var mm=[68,39,43,160,45,33,116,240,251,156,45,31,225,255,45,22,140,155,112,144,214,47,152,233,164,146,168,3,253,29,123,37]
            // ptr(rax).writeByteArray(mm); 
        }
    })
   addr = sgame.base.add(0x5DF1A811A0 - 0x05DF1A7F000)
    console.log("" + addr);
    console.log(Instruction.parse(addr).toString());
    Interceptor.attach(addr, {
        onEnter: function (args) {
            var rax = this.context.x8;
             console.log(hexdump(ptr(rax), { length: 50, ansi: true }));
             time(5451)
        }
    })
}, 1) 

直接可以拿到表

写出解密代码

#include <stdio.h>

char flag[]="AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
unsigned char mm[32] = {
    0x50, 0x4C, 0x8B, 0x94, 0x86, 0x6D, 0x72, 0xFB, 0x54, 0xF3, 0x17, 0x0F, 0xEE, 0xE4, 0xC5, 0x1E, 
    0xB8, 0x1A, 0xC7, 0xDF, 0x2D, 0x3D, 0x4E, 0x51, 0xE7, 0xAD, 0x97, 0x55, 0xF3, 0xF5, 0x41, 0x79
};
unsigned char box[]={0x36,0x71,0xf4,0x67,0xfa,0x9a,0xf9,0x0a,0x5e,0xa0,0xb6,0xb0,0x11,0xab,0x7a,0x2d,0xd0,0xd3,0x0a,0xca,0xe8,0x91,0x9a,0xc2,0x64,0x8e,0x12,0x08,0xba,0x46,0x4a,0x6e};
int main(){
    // int n=0;
   unsigned char xor2=0;
   unsigned char keys[40];
    for (size_t i = 0; i < 32; i++)
    {
        if (i!=0) {
        	xor2^=mm[i-1];
        	keys[i]=xor2;
    	}
   	}
        for (size_t i = 0; i <32; i++)
    {
        // flag[i]^=i;
        if (i!=0)
        {
            mm[i]^=keys[i];
        }    
    }
    for (size_t i = 0; i < 32; i++)
    {
        mm[i]^=i;
        mm[i]^=box[i];
        printf("%c", mm[i]);
    }
}
//flag{welcome-re-world!go!go!go!}