XORSelection is a 010 Editor script I wrote some time ago, and it is included in the 010 Editor script repository. You provided it with an XOR key (ASCII or HEX), and then it will XOR-encode the file (or selection) open in 010 Editor.
I discovered it will not work properly if the hexadecimal key contains a NULL byte (0x00). This is fixed in this new version.
This new version also allows whitespace characters when an hexadecimal key is provided (hexadecimal keys start with 0x).