#113: Google CTF

Easy challenges (part 1/2).
4:57 Intro
18:07 Hardware / Basics
1:00:14 Crypto / Chunk Norris (failed to solve; restart in part 2)
1:37:29 Pwn / Tracing
2:41:19 Reversing / Beginner

Our IRC: #gynvaelstream-en on freenode

[professorx]

Came here from The cyber Mentor .. You are a genius ❤️ Thanks for this video, learnt a lot 👍

[krzysztof-wsog]

Hardware: What about just taking screenshot of bit representation and just moving ( or flipping ) them around in image editor
believe it would be easier than drawing on piece of paper

[BrainFood]

Anybody have timestamp links to specific challs?

[sentdc]

2:44:27 dude, you're overcomplicating that last SIMD instructions challenge. After the shuflle (pshufb instruction) you basically have 4 dwords, that you add constants to, then xor with another constant and finally compare with strncmp. So to get each original dword, you basically revert the order. Take whatever strncmp was comparing it to, xor it with the constant used, then subtract another constant. Do this for each 4 dwords. Then all you have left to do is to combine all 4 dwords and reverse-shuffle the resulting 128-bit xmm0 byte by byte like that pshufb instruction was doing. And that is it. There's no need for some z3 library or anything else.