CryptoHack Hints

General:

This challenge set requires a little knowledge of math and general stuff. Thus, I won’t give out the detailed hints for all challenges.

1. XOR:

• Favorite byte: The flag character by character is xored with a single byte. To find the hidden byte, you can use the flag format of crypto{ .
• You either know, XOR you don’t: It is quite similar to the Favorite byte challenge as you can find the key with the flag format. It won’t give you the complete key, but your brain will tell you all :D.
• Lemur XOR: This seems to be a hard challenge at first. Take a look at the XOR Properties and think how to clear out the key. m1 = p1 XOR key. m2 = p2 XOR key. So what if m1 XOR m2?

2. Mathemetics:

• Greatest Common Divisor: You can use the gmpy2 package to solve this chall.
• Extended GCD: As p, q are prime, gcd(p,q) = 1. You should build a Python implementation of Extended Euclidean algorithm with this pseudocode.
• Modular Inverting: The Fermat’s little theorem said that a^p ≡ a mod p. So what if we multiply both sides with a^-1. A little more math will take you to the flag.

3. Data Format:

• Transparency: I want to give hints for this chall because at the time I write this, it has less than 400 solves. A small (I don’t know, maybe big) hint is to find the subdomain of cryptohack.org

Mathematics:

Before starting this challenge set, you should get yourself ready with enough Math to avoid being confused like me was. coming soon~~