Answer separate into 4 hints so the solution isn't spoilered all at once:



Hint 1: December is month number 12, July is month number 7






Hint 2: That gives you "12 , 17" and "25 , 7" --> You only need 4 digits so you can do some simple math here






Hint 3: How about basic additions?






Hint 4: How about adding up 12 and 17 for the first two digits of the code, and then adding up 25 and 7 for the last two digits?

ahh geeze, I thought I did that. Obviously I did not and looked too much into this one :/

thanks!