💹Simple Encryptor

https://app.hackthebox.com/challenges/Simple%2520Encryptor

main

  local_10 = *(long *)(in_FS_OFFSET + 0x28);
  local_30 = fopen("flag","rb");
  fseek(local_30,0,2);
  local_28 = ftell(local_30);
  fseek(local_30,0,0);
  local_20 = malloc(local_28);
  fread(local_20,local_28,1,local_30);
  fclose(local_30);
  tVar2 = time((time_t *)0x0);
  local_40 = (uint)tVar2;
  srand(local_40);
  for (local_38 = 0; local_38 < (long)local_28; local_38 = local_38 + 1) {
    iVar1 = rand();
    *(byte *)((long)local_20 + local_38) = *(byte *)((long)local_20 + local_38) ^ (byte)iVar1;
    local_3c = rand();
    local_3c = local_3c & 7;
    *(byte *)((long)local_20 + local_38) =
         *(byte *)((long)local_20 + local_38) << (sbyte)local_3c |
         *(byte *)((long)local_20 + local_38) >> 8 - (sbyte)local_3c;
  }
  local_18 = fopen("flag.enc","wb");

Timestamp flag.enc

╰─ stat flag.enc                                                                                                                                                                                              ─╯
  File: flag.enc
  Size: 32              Blocks: 0          IO Block: 512    regular file
Device: 0,179   Inode: 12666373952038248  Links: 1
Access: (0777/-rwxrwxrwx)  Uid: ( 1000/    kali)   Gid: ( 1000/    kali)
Access: 2024-10-05 01:14:37.623928000 +0200
Modify: 2022-07-19 13:14:48.000000000 +0200
Change: 2024-10-05 01:14:32.437619400 +0200
 Birth: -

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

int main(void) {
    typedef unsigned char byte;
    FILE *f;
    size_t flagSize;
    byte *flag;
    unsigned int seed;
    long i;
    int rnd1, rnd2;

    f = fopen("flag.enc", "rb");
    // seek until the end of the file to get the size
    fseek(f, 0, SEEK_END);
    flagSize = ftell(f);
    // seek to the beginning
    fseek(f, 0, SEEK_SET);
    // allocate memory of the flag
    flag = malloc(flagSize);
    fread(flag, 1, flagSize, f);
    fclose(f);

    // take seed from the first 4 bytes
    int flagOffset = 4;
    memcpy(&seed, flag, flagOffset);
    srand(seed);

    for(i = flagOffset; i < (long)flagSize; i++) {
        rnd1 = rand();
        rnd2 = rand();
        rnd2 = rnd2 & 7;
        flag[i]  = 
            flag[i] >> rnd2 |
            flag[i] << 8 - rnd2;
        flag[i] = rnd1 ^ flag[i];
        printf("%c", flag[i]);
    }
}

╰─ gcc exploit.c -o exploit                                                                                                                                                                                   ─╯

╰─ ./exploit                                                                                                                                                                                                  ─╯
HTB{vRy_s1MplE_F1LE3nCryp0r}%