Hidden Flag, XORing Data, HSCTF6 Writeup - Marsの5εcur1ty備忘録

Description:

This image seems wrong.....did Keith lose the key again?

We first get a file with png extension which is unable to open as a png file.

f:id:z773733850:20190612131444p:plain

Then we output the hex data, and we can find that there are no png signature '89 50 4E 47 0D 0A 1A 0A'.
f:id:z773733850:20190612132253p:plain

Let's review the description:
This image seems wrong.....did Keith lose the key again?

We could consider using XOR. First we could try 'again' as the key.

f:id:z773733850:20190612132418p:plain

No signature. The key seems wrong.

So, we show the hex data of chall.png one more time. As we can see that 'key is invisible' is shown.

f:id:z773733850:20190612132641p:plain

Let's try the key 'invisible'.

f:id:z773733850:20190612132729p:plain

We got it! Just output the data as a png file.

f:id:z773733850:20190612132840p:plain

f:id:z773733850:20190612132944p:plain

Got the flag.