One Bite

Category: Rev
Points: 60
Description: Whenever I have friends over, I love to brag about things that I can eat in a single bite. Can you give this program a tasty flag that fits the bill?

I feel like i’m cheating when im using ghidra. Anyway this binary takes some input and then if it is the right input (the flag in this case) it says correct!

Popping the binary into ghidra looking at the main function, the main bit of code that stands out is this bit:


  while( true ) {
    sVar2 = strlen((char *)local_48);
    if (sVar2 <= (ulong)(long)local_54) break;
    local_48[(long)local_54] = local_48[(long)local_54] ^ 0x3c;
    local_54 = local_54 + 1;
  }
  iVar1 = strcmp((char *)local_48,"]_HZGUcHTURWcUQc[SUR[cHSc^YcOU_WA");

The last line I thought I could just give to the program and it would gimme the flag but nonono.

The code above it is XOR’ing the input that you give it with 0x3c with is 60 in decimal.

So I popped the hardedcoded pw in cyberchef, XOR with decimal 60 and boom out popped the flag.

FLAG

actf{i_think_im_going_to_be_sick}

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