Original Author writeup:

https://www.abs0lut3pwn4g3.cf/writeups/2019/04/04/encryptctf-journeytothecentreofthefile1.html

Original writeup (https://www.abs0lut3pwn4g3.cf/writeups/2019/04/04/encryptctf-journeytothecentreofthefile1.html).