tl;dr Chosen Ciphertext Attack based on Tencent's QQ Browser vuln: [https://arxiv.org/abs/1802.03367](https://arxiv.org/abs/1802.03367)
Full writeup: [https://masterpessimistaa.wordpress.com/2018/10/14/inctf-2018-crypto-writeups-part-2/](https://masterpessimistaa.wordpress.com/2018/10/14/inctf-2018-crypto-writeups-part-2/)