Crypto

Challenge Information category: crypto points: 235 Description Easy lfsr easy crypto 链接：https://share.weiyun.com/5qZbNLR 密码：n9huwc https://drive.google.com/open?id=1a5GMVZ77CM1rOrayKJcV3UvMwAy-uGsg Writeup Author 0ssigeno meowmeowxw Solution To understand how a general nlsr works, please read this article from ctfwiki. What did we learn from that article? That we must find a strong correlation between the output and one of the input. So we made a little script to retrieve the truth table of (ao * bo) ^ (bo * co) ^ (bo * do) ^ co ^ do The table retrieved is the following: ...

The challenge use a classic RSA sign and verify, without anything strange. So, differently from the others, I abused the fact that we can give both the Sign and the plaintext as inputs. Is enought to switch S with M when given as input, where S is calculated encrypting M with the public key that is given. Since verify(m,s): return m==encrypt(s,publickey) If we give verify(encrypt("AAAA",publicKey),"AAAA") # encrypt("AAAA",publickey)==encrypt("AAAA",publickey) we will pass the test. We just have to do this for 3 times! Image not found! ...