2021.6.1萌新赛 re wp

比赛做了两道，剩下有道sm4加密，只不过要去平坦化控制流，本来以前做xctf环境都搭好了，可以用deflat.py去，结果现在又用不了了。。。。难受，还有两道apk题，确实apk做得少，不当做得来。

re_signin

中午放学回来做起得，还没放hint，后来放了hint，难度直接下降。

还是pyc先转py，然后看逻辑

实际上后面还有个位移量为13的凯撒

脚本

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#include<stdio.h>

void BubbleSort(int a[], int len)
{
	int i, j, temp,n=0;
	for (j = 0; j < len - 1; j++)
	{
		for (i = 0; i < len - 1 - j; i++)
		if (a[i] > a[i + 1])
		{
			temp = a[i];
			a[i] = a[i + 1];
			a[i + 1] = temp;
			n++;
		}
	}
	printf("%c",n);
}
 
int main()
{
	int arr[24][22] = {{73, 69, 60, 20, 64, 68, 99, 4, 36, 9, 91, 42, 75, 43, 8, 77, 55, 70, 84, 37, 3, 93},
{85, 46, 47, 99, 58, 35, 83, 3, 57, 18, 52, 17, 97, 16, 6, 51, 84, 62, 1, 41, 88, 87},
{97, 34, 31, 80, 19, 57, 10, 84, 4, 50, 43, 63, 65, 88, 30, 72, 21, 36, 27, 41, 86, 79},
{31, 23, 68, 67, 30, 47, 27, 40, 73, 63, 11, 89, 18, 5, 9, 74, 88, 38, 8, 20, 50, 83},
{88, 5, 85, 82, 36, 74, 6, 15, 40, 55, 95, 8, 84, 47, 96, 33, 25, 29, 77, 67, 26, 39},
{54, 53, 0, 37, 66, 91, 39, 38, 57, 6, 47, 28, 49, 92, 29, 85, 88, 84, 90, 13, 35, 52},
{80, 18, 26, 91, 10, 52, 11, 99, 85, 75, 60, 48, 36, 74, 55, 51, 86, 49, 89, 29, 82, 16},
{35, 70, 42, 44, 18, 65, 84, 71, 26, 14, 38, 28, 21, 86, 20, 54, 30, 11, 66, 10, 69, 77},
{71, 25, 43, 23, 29, 6, 33, 44, 5, 30, 32, 18, 47, 13, 76, 8, 83, 87, 57, 26, 16, 19},
{29, 51, 7, 62, 94, 32, 57, 1, 71, 84, 92, 16, 18, 19, 56, 52, 40, 80, 98, 44, 82, 33},
{67, 14, 93, 91, 78, 80, 7, 37, 10, 82, 38, 83, 23, 27, 17, 76, 74, 18, 66, 24, 99, 43},
{29, 56, 44, 54, 70, 31, 10, 38, 8, 85, 18, 22, 32, 49, 2, 21, 50, 5, 25, 48, 90, 84},
{23, 33, 90, 7, 42, 71, 25, 58, 5, 47, 54, 18, 97, 72, 2, 1, 68, 64, 76, 85, 69, 49},
{77, 67, 52, 31, 35, 6, 56, 94, 81, 23, 78, 50, 15, 10, 28, 69, 43, 91, 82, 72, 99, 38},
{20, 47, 52, 27, 73, 64, 9, 62, 3, 57, 2, 97, 44, 35, 89, 10, 18, 29, 58, 56, 74, 84},
{66, 11, 76, 91, 70, 9, 6, 75, 32, 71, 44, 48, 88, 20, 98, 97, 79, 63, 47, 78, 60, 81},
{43, 13, 70, 23, 31, 69, 52, 30, 2, 78, 0, 37, 73, 93, 18, 1, 51, 62, 25, 68, 65, 87},
{24, 86, 29, 0, 93, 51, 53, 47, 16, 40, 94, 98, 88, 64, 41, 83, 44, 35, 45, 75, 17, 46},
{33, 12, 63, 77, 25, 24, 47, 58, 6, 89, 97, 27, 21, 96, 92, 50, 82, 76, 5, 62, 56, 44},
{12, 36, 16, 44, 19, 62, 43, 80, 58, 98, 69, 97, 1, 7, 49, 26, 70, 34, 53, 13, 65, 48},
{51, 74, 76, 98, 33, 78, 44, 45, 4, 65, 99, 84, 80, 93, 37, 56, 77, 9, 6, 94, 52, 88},
{80, 38, 88, 66, 7, 40, 70, 24, 2, 12, 76, 18, 57, 73, 58, 83, 33, 17, 89, 69, 77, 67},
{18, 53, 14, 24, 94, 42, 61, 75, 62, 60, 73, 2, 65, 48, 80, 23, 44, 91, 7, 0, 31, 71},
{16, 54, 87, 75, 8, 23, 33, 56, 22, 63, 1, 2, 25, 6, 84, 80, 4, 49, 17, 42, 14, 43}};
	int i = 0;

 	for(i=0;i<24;i++)
 	{
 		BubbleSort(&arr[i][0], 22);
	}
	return 0;
}
//synt{jrypbzr_gb_arjfpgs}

然后凯撒位移13，得到flag{welcome_to_newsctf}

1+1的签到题

考点，upx脱壳，伪随机数，变表base64，变表base58

先看伪随机数，系统不同产生的随机数也会不一样，这里我为了方便，直接就动调得到的随机数。

脚本

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#include<stdio.h>

int main()
{
	int v2;
	__int64 a1;
	int i; 
	char ch;
	v2=0xBD46588;
	a1=(__int64)(0x1d7ccbb80^0xBD46588^0x235FFFA864 ^ 0x67B7940F53);
	
	for(i=0;i<5;i++)
	{
		ch=a1>>((4-i)*8)&0xff;
		putchar(ch);
	}
}
//E4sy?

接下来就是两个secret

secret1

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import base58

code='ZoJPRqxMfvzxNqu'

table1='ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz123456789'
table2='123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
code2=''
flag=''
for i in range(len(code)):
    for j in range(len(table1)):
        if code[i]==table1[j]:
            code2+=table2[j]
            break
#print(code2)
flag=base58.b58decode(code2)
print(flag)
#_Up_t0_Y0u!

secret2

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str1 ='ITFDNG5nejSVfUFcfGssbjVcIR=='
string1 = 'ABCDEFGHIJKMNLOPRSTUVQWYXZabefghicdjklmnopqtuvwrsxyz0123456789+/'
string2 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

print(base64.b64decode(str1.translate(str.maketrans(string1, string2))))
#!!C0ngr4Tu1atl0n5!!

得到flag{Eys4?_Up_t0_Y0u!!!C0ngr4Tu1atl0n5!!}

Qsay

文件有3个，一个key，一个dll，一个exe。根据后面分析dll可以知道key是sm4的key，exe是密文，32个字节，dll是sm4加密过程，可以用findcryto插件找到特征值。

定位到加密函数，发现。

感觉用了平坦化控制流，但是用delat.py没去掉，然后直接用sm4脚本解，解不出来，怀疑魔改了数据。去看数据，一对比，确实魔改了。

然后用自己之前写的sm4脚本解密，也可以用GitHub上的https://github.com/Leeyuxun/C-SM4

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#include<stdio.h>

unsigned int FK[4] = {
0xa3b1bac6,
0x56aa3350,
0x677d9197,
0xb27022dc
};

/******************************定义固定参数CK的取值****************************************/
unsigned int CK[32] = {

0x00070e15,0x1c232a31,0x383f464d,0x545b6269,
0x70777e85,0x8c939aa1,0xa8afb6bd,0xc4cbd2d9,
0xe0e7eef5,0xfc030a11,0x181f262d,0x343b4249,
0x50575e65,0x6c737a81,0x888f969d,0xa4abb2b9,
0xc0c7ced5,0xdce3eaf1,0xf8ff060d,0x141b2229,
0x30373e45,0x4c535a61,0x686f787d,0x848b9299,
0xa0a7aeb5,0xbcc3cad1,0xd8dfe6ed,0xf4fb0209,
0x10171e25,0x2c333a41,0x484f565d,0x646b7279
};

/******************************SBox参数列表****************************************/
unsigned char SBOX[256] = {

   0xC6,0x90,0xe9,0xfe,0xcc,0xe1,0x3F,0xb7,0x16,0xb6,0x14,0xc2,0x28,0xfb,0x2c,0x05,
0x2b,0x67,0x9a,0x76,0x2C,0xbe,0x04,0xc3,0xaa,0x44,0x13,0x26,0x49,0x86,0x06,0x99,
0x9c,0x42,0x50,0xf4,0x91,0xef,0x98,0x7a,0x33,0x54,0x0b,0x43,0xed,0xcf,0xac,0x62,
0xe4,0xb3,0x1c,0xa9,0xc9,0x08,0xe8,0x95,0x80,0xdf,0x94,0xfa,0x75,0x8f,0x3f,0xa6,
0x47,0x07,0xa7,0xfc,0xf3,0x73,0x17,0xba,0x83,0x59,0x3c,0x19,0xe6,0x85,0x4f,0xa8,
0x68,0x6b,0x81,0xb2,0x71,0x64,0xda,0x8b,0xf8,0xeb,0x0f,0x4b,0x70,0x56,0x9d,0x35,
0x1e,0x24,0x0e,0x5e,0x63,0x58,0xd1,0xa2,0x25,0x22,0x7c,0x3b,0x01,0x21,0x78,0x87,
0xd4,0x00,0x46,0x57,0x9f,0xd3,0x27,0x52,0x4c,0x36,0x02,0xe7,0xa0,0xc4,0xc8,0x9e,
0xea,0xbf,0x8a,0xd2,0x40,0xc7,0x38,0xb5,0xa3,0xf7,0xf2,0xce,0xf9,0x61,0x15,0xa1,
0xe0,0xae,0x5d,0xa4,0x9b,0x34,0x1a,0x55,0xad,0x93,0x32,0x30,0xf5,0x8c,0xb1,0xe3,
0x1d,0xf6,0xe2,0x2e,0x82,0x66,0xca,0x60,0xc0,0x29,0x23,0xab,0x0d,0x53,0x4e,0x6f,
0xd5,0xdb,0x37,0x45,0xde,0xfd,0x8e,0x2f,0x03,0xff,0x6a,0x72,0x6d,0x6c,0x5b,0x51,
0x8d,0x1b,0xaf,0x92,0xbb,0xdd,0xbc,0x7f,0x11,0xd9,0x5c,0x41,0x1f,0x10,0x5a,0xd8,
0x0a,0xc1,0x31,0x88,0xa5,0xcd,0x7b,0xbd,0x2d,0x74,0xd0,0x12,0xb8,0xe5,0xb4,0xb0,
0x89,0x69,0x97,0x4a,0x0c,0x96,0x77,0x7e,0x65,0xb9,0xf1,0x09,0xc5,0x6e,0xc6,0x84,
0x18,0xf0,0x7d,0xec,0x3a,0xdc,0x4d,0x20,0x79,0xee,0x5f,0x3e,0xd7,0xcb,0x39,0x48
};

void long_to_char(unsigned int in ,unsigned char *out)
{
    int i;

    for(i=0;i<4;i++)
    {
        out[i]=(unsigned char)(in>>(24-i*8))&0xff;
    }
}
void char_to_long(unsigned char *in , unsigned int *out)
{
    int i;
    *out=0;
    for(i=0;i<4;i++)
    {
        *out = (unsigned int)in[i]<<(24-8*i)|(*out);
    }
}

unsigned int left_move(unsigned int a,int lenth)
{
    a=(a<<lenth) | a>>(32-lenth);
    return a;
}

unsigned int date_round(unsigned int tmp)
{
    int i;
    unsigned char arr[4]={0};
    long_to_char(tmp,arr);

    for(i=0;i<4;i++)
    {
        arr[i]=SBOX[arr[i]];
    }
    char_to_long(arr,&tmp);
    tmp = tmp ^ left_move(tmp, 2) ^ left_move(tmp, 10) ^ left_move(tmp, 18) ^ left_move(tmp, 24);

    return tmp;
}

void sm4_encode(unsigned char *plain,unsigned int sub_key[],unsigned char out[])
{
    int i;
    unsigned int date[36];

    for(i=0;i<4;i++)
    {
        char_to_long(plain+i*4,date+i);
    }

    for(i=0;i<32;i++)
    {
        date[i+4]=date[i]^date_round(date[i+1]^date[i+2]^date[i+3]^sub_key[i+4]);
    }

    for(i=0;i<4;i++)
    {
        long_to_char(date[35-i],out+i*4);
    }

}

void sm4_decode(unsigned char *code,unsigned int sub_key[],unsigned char out[])
{
    int i;
    unsigned int date[36];

    for(i=0;i<4;i++)
    {
        char_to_long(code+i*4,date+i);
    }

    for(i=0;i<32;i++)
    {
        date[i+4]=date[i]^date_round(date[i+1]^date[i+2]^date[i+3]^sub_key[35-i]);
    }

    for(i=0;i<4;i++)
    {
        long_to_char(date[35-i],out+i*4);
    }

}

unsigned int key_round(unsigned int tmp)
{
    int i;
    unsigned char arr[4]={0};
    long_to_char(tmp,arr);

    for(i=0;i<4;i++)
    {
        arr[i]=SBOX[arr[i]];
    }
    char_to_long(arr,&tmp);
    tmp = tmp ^ left_move(tmp, 13) ^ left_move(tmp, 23);
    return tmp;
}

void extendkey(unsigned char key[],unsigned int sub_key[])
{
    int i;

    for(i=0;i<4;i++)
    {
        char_to_long(key+i*4,sub_key+i);
        sub_key[i]^=FK[i];
    }

    for(i=0;i<32;i++)
    {
        sub_key[i+4]=sub_key[i] ^ key_round(sub_key[i+1] ^ sub_key[i+2] ^ sub_key[i+3] ^ CK[i]);
    }

}

int main(void)
{
    unsigned char key[16] ={0x4D, 0x4C, 0x7B, 0x4F, 0xAB, 0x6B, 0x78, 0x09, 0xE6, 0x27, 0xFA,
0x9D, 0xA6, 0xC6, 0x4E, 0x8A };
    unsigned char code[32]={0xAF, 0xD3, 0xD5, 0x71, 0x1F, 0xC6, 0xA3, 0x42, 0xC5, 0x64, 
  0x53, 0x2E, 0xFE, 0x13, 0xF1, 0xA3,0x0F, 0x96, 0x0A, 0x0B, 0x1D, 0x3D, 0x83, 0x33, 0x2A, 0x4B,
0x71, 0x98, 0x10, 0xFF, 0x70, 0x43};
    unsigned int sub_key[36]={0};    
    unsigned char out[32];
    int i;

    extendkey(key,sub_key);

    sm4_decode(code,sub_key,out);
    sm4_decode(&code[16],sub_key,&out[16]);
    for(i=0;i<32;i++)
    {
        printf("%c",out[i]);
    }
 }
//newsctf{QSay1ts-1nTereStingObf}

开门啊-1

apk还是做少了，逻辑看起都费劲，看wp学习了一下。而且想jeb动调来着，结果不知道什么原因，程序老是闪退，也不知道是不是Android环境不对。

分析主函数

分析tom1函数
、

脚本

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#include<stdio.h>

int main()
{
	int flag[20]={0x7A, 0x74, 0x7F, 0x79, -123, 0x4F, 74, 76, 71, 72, 77, 75, 74, 73, 76, 74, 76, 77, 76, -125};
	int i;
	for(i=0;i<20;i++)
	{
		flag[i]=(flag[i]^15)-15;
		printf("%c",flag[i]);
	}
}
//flag{16498356746434}

开门啊-2

不知道为什么，so文件和wp的函数伪代码差距也太大了吧，不做了，杀鸡去了，嘿嘿嘿。