The postscript code turned out to be a simple repeated xor cipher. Get the target string and then decrypt it to get the input.

https://github.com/rsa-ctf/write-ups/blob/master/2018/squarectf18/C9-postfuscator/README.md

Original writeup (https://github.com/rsa-ctf/write-ups/blob/master/2018/squarectf18/C9-postfuscator/README.md).