This was a fun and in the end straitforward challenge, where a funky RSA-like cryptosystem that uses a modulus which is the product of 4 primes generated in an interesting way.

The public key includes one of the four prime factors of the modulus, and the flag is encrypted without padding so this factor alone can be used to decrrypt the flag.

Original writeup (https://4cad.github.io/CTF_Writeups/202008%20CryptoCTF/ThreeRavens/CryptoCTF20%20-%20Three%20Ravens%20Writeup.html).