delf

关键函数

__int64 __fastcall encrypt(const char *a1)
{
  __int64 result; // rax
  char v2; // [rsp+13h] [rbp-Dh]
  int v3; // [rsp+14h] [rbp-Ch]
  int j; // [rsp+18h] [rbp-8h]
  int i; // [rsp+1Ch] [rbp-4h]

  v3 = strlen(a1);
  for ( i = 0; i < v3; ++i )
    a1[i] ^= 0x5Au;
  for ( j = 0; ; j += 2 )
  {
    result = (unsigned int)(v3 - 1);
    if ( j >= (int)result )
      break;
    v2 = a1[j];
    a1[j] = a1[j + 1];
    a1[j + 1] = v2;
  }
  return result;
}

script:

f = open(r"C:\Temp\encrypted.bin", "rb").read()

print(f.decode())


def decrypt(x):
    flag = ""
    flagg = ""
    for i in range(0, len(x) - 1, 2):
        flag += x[i + 1] + x[i]
    for j in flag:
        flagg += chr(ord(j) ^ 0x5A)
    print(flag)
    print(flagg)


decrypt(f.decode())
#The_end_of_the_world_is_binary
#flag{9ac39760c3195f2474f31291bc558798}

或c

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
 

void decrypt(char *x) { 
    int len = strlen(x); 
    char flag; 
    char flagg[1024]; 
    int i, j; 
    for (i=0;i<strlen(x);i+=2){
      flag = x[i];
      x[i] = x[i+1];
      x[i+1] = flag;
    }

 
    for (j = 0; j < strlen(x); j++) { 
        flagg[j] = x[j] ^ 0x5A; 
    } 
    printf("%s\n",x);
    printf("%s\n", flagg); 
} 
 
int main() { 
    FILE *file; 
    file = fopen("C:\\Temp\\encrypted.bin",  "rb"); 
    fseek(file,0,SEEK_END);
    int len = ftell(file);
    fseek(file,0,SEEK_SET);
    printf("file_len:%d\n",len);
    char* buf = (char*)malloc(len);
    fread(buf, sizeof(char),len, file); 
    buf[len]='\0';
    printf("%s\n",buf);
    decrypt(buf); 
 
    return 0; 
}