Simple stream cipher with known pt attack, full writeup:

[https://ctf.rip/write-ups/crypto/rsa/reversing/rarctf-2021/#minigen](https://ctf.rip/write-ups/crypto/rsa/reversing/rarctf-2021/#minigen)

Original writeup (https://ctf.rip/write-ups/crypto/rsa/reversing/rarctf-2021/#minigen).