As I understand it, the first word is the "key" anyway.
You just need to get that one right.
They put the second word up as a trial, and rather than using it as a pass key, they merely collect people's attempt at the word. If the responses vary wildly, the word is too complex and they won't use it. If the vast majority enter the second word correctly, then it's readable so they add it to the list of "key" words.
I can't remember where I heard or read that they were using the technique.
So anyway, as long as you enter "source" correctly, you should be fine.