VolgaCTF 2017 Quals - VC - Crypto

Informations

Version

By Version Comment
noraj 1.0 Creation

CTF

Description

There are files A.png and B.png. But where's the flag?

A.png

B.png

A.png:

A

B.png:

B

Solution

If you know OTP you must know this famous attack on pad reused.

You can also see some black lines on image B. Now let's XOR image A and B (with ImageMagick):

1
$ convert A.png B.png -fx "(((255*u)&(255*(1-v)))|((255*(1-u))&(255*v)))/255" out.png

And now we get the result:

out

Flag is: VolgaCTF{Classic_secret_sharing_scheme}.

Note: VC is for Visual Cryptography

Share