Bitwise with Hex && Hex to String

Hi Thanks for your help I'll just describe what I want to do any advice or if you could provide your own example it would really help, thanks again!

I have a string holding hex numbers "41495ab3edde720c" and I want to get those values out of the string and represent them as hexadecimal thus 0x41495ab3edde720c, then I want to xor that hex with another hex like 

0x41495ab3edde720c ^ 0x1111111111111111

then I want to take the result which will be in this example (50584BA2FCCF631D)

and turn it back into a string "50584BA2FCCF631D"

I'm not that good with php it seems hard to do this easily?