jonathas-conceicao / pba_many_time_pad

2023/01/10 pratical assigment from Polkadot Blockchain Acadamey

Cryptography Many Time Pad

Description

We a message sample that was said to have ciphered messages that used the same time pad key multiple times. Our task was the exploit this issue in order to find out the actual content off all the messages.

Solution

Our approach to it was to:

• Implement the cipher function, a bit-wise XOR operation to be performed between two strings;
• Decode input into strings, which was given in hexadecimal encoding;
• Perform a dragging XOR using common English words over the length of of the result of XORing two of the known ciphers in order to find familiar words related to the key
• Once enough dragging had been done we were able to find the key and cipher it over the ciphered messages in order to find their original content

Related links and tips

Notion post about the problem

Tips given during the assignment:

Here are the hints so far:

The messages (and if you didn’t change it this time, the key) are in english, unicode encoded. The inverse of XOR is XOR itself. XOR is a bitwise operation, and characters for messages are UTF-8 encoded XOR the ciphertexts together, and consider what happens when a space is XORed with a character in [a-zA-Z]. Consider Crib dragging: https://samwho.dev/blog/toying-with-cryptography-crib-dragging/ . (This is basically a full solution to find the key, and should unblock almost everyone)