Tags: elliptic curves 

Rating: 5.0

1. Search a Elliptic curve with smooth order
2. Recover the full index of y using Pohlig-hellman
3. Recover the index of y in each subgroup with naive discrete log
4. Optimize it very hard
5. Find a server in Germany
6. Calculate y

Original writeup (https://sasdf.cf/ctf/writeup/2018/hxp/crypto/blinder/).